freecalypso-docs: FC-handset-spec annotate

annotate FC-handset-spec @ 51:7933c3a1b5e0

FC-handset-spec: power domain mess documented

author	Mychaela Falconia <falcon@freecalypso.org>
date	Fri, 11 Jun 2021 08:04:44 +0000
parents	da1a2a32c260
children	cfe8623b915d

rev	line source
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	1 FreeCalypso Handset Specification
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	2 =================================
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	3
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	4 The purpose of this document is two-fold:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	5
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	6 1) This document serves as the principal design specification for the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	7 FreeCalypso Libre Dumbphone handset hardware which I, Mother Mychaela,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	8 seek to build.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	9
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	10 2) This document also defines the scope of functionality to be supported in
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	11 FreeCalypso handset firmware, including support for additional hardware
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	12 targets beyond the primary FC handset hw target.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	13
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	14 1. FC handset hardware specification
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	15
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	16 1.1. Basic features
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	17
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	18 The Mother's goal is to produce a replacement for the proprietary Pirelli DP-L10
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	19 phone, or more specifically, for the GSM-only subset of this Pirelli phone which
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	20 the Mother actually uses, without Pirelli's key differentiating feature of
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	21 non-GSM WiFi operation, and without Pirelli's camera. The following hardware
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	22 features are to be included:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	23
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	24 * 176x220 pixel color display (no touch)
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	25 * 21-button main keypad
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	26 * 3 side buttons for volume control and an auxiliary function
42 6b61d77f7700 FC-handset-spec: missed the loudspeaker and vibrator in 1.1 Mychaela Falconia <falcon@freecalypso.org> parents: 41 diff changeset	27 * hands-free loudspeaker
6b61d77f7700 FC-handset-spec: missed the loudspeaker and vibrator in 1.1 Mychaela Falconia <falcon@freecalypso.org> parents: 41 diff changeset	28 * vibrator
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	29 * USB port that combines charging and computer interface
46 1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	30 * wired analog headset jack
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	31 * single SIM slot
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	32
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	33 The following features which are commonly found in mainstream proprietary
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	34 phones, particularly more recent ones, will NOT be included:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	35
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	36 * camera
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	37 * Bluetooth
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	38 * FM radio
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	39 * TV receiver
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	40 * GPS receiver
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	41 * dual SIM slot
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	42 * torch light beyond LCD and keypad backlights
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	43
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	44 1.2. RF band capability
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	45
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	46 Our FC handset needs to be quadband GSM; this quadband capability will be
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	47 achieved by copying the RF section and the core PCB layout around it from the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	48 reverse-engineered iWOW TR-800 modem module, which is itself a very direct
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	49 (almost verbatim) derivative of TI's Leonardo+ quadband reference design.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	50
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	51 1.3. RAM and flash
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	52
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	53 The Mother's intent is to use Spansion S71PL064JA0 flash+RAM MCP on the final
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	54 handset motherboard, providing 8 MiB of flash and 2 MiB of XRAM in a 7x9 mm
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	55 footprint. This flash and RAM capacity is already known to be fully sufficient
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	56 for our FreeCalypso handset firmware in maximal feature configuration, hence
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	57 any larger capacity would be excessive. However, on our FC Venus development
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	58 board we may use the larger S71PL129NC0 MCP, same as used on FCDEV3B V2.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	59
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	60 1.4. Liquid crystal display
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	61
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	62 1.4.1. Display size
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	63
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	64 The size of the display for our FC Libre Dumbphone handset design is fixed at
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	65 176x220 pixels, 16-bit color, following TI's D-Sample platform and the starting
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	66 point UI code that was developed for it. Thoughts of changing to a different
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	67 display size have been considered and rejected:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	68
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	69 * If we were to change to a smaller display size, we would have to do extra work
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	70 on the firmware to shrink the UI to the smaller size, and we would reduce the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	71 amount of information that can be displayed at once. We would incur extra
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	72 work and a functional loss, but gain absolutely nothing in return.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	73
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	74 * If we were to change to a larger display size (240x320 pixels seems to be the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	75 largest reasonable size for dumbphones, used in high-end Nokia models), we
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	76 would be venturing into uncertain territory - the greatest uncertainty would
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	77 be the extra CPU load on Calypso to draw the larger UI and to refresh the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	78 larger framebuffer, which is done with PIO on Calypso, without any DMA
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	79 assistance. The D-Sample LCD size of 176x220 pixels already appears to be a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	80 strain in some drawing code paths, hence the Mother's decision is to play it
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	81 safe and stick with the known working display size. Expanding the UI to make
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	82 sensible use of larger screen real estate would also entail additional work.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	83
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	84 176x220 is the display size in pixels, and this resolution number by itself says
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	85 nothing about the physical display size in inches or mm. However, most readily
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	86 available LCDs that are made for this pixel resolution are made in 2.0" diagonal
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	87 physical size, with 31.68x39.60 mm active area and 0.180 mm dot pitch, hence
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	88 this physical size is the one we are going to use.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	89
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	90 1.4.2. Specific LCD module selection
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	91
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	92 As of this writing, the specific LCD module to be used has not been firmly
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	93 selected yet. We are actively looking for an LCD module that fits all of the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	94 following requirements:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	95
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	96 * TFT color LCD, 2.0" diagonal, 176x220 pixel resolution;
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	97
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	98 * 16-bit microprocessor bus interface;
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	99
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	100 * 6:00 viewing direction as appropriate for cellular handsets;
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	101
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	102 * backlight consisting of 3 white LEDs in parallel, joined at the anode,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	103 with separately brought-out cathodes;
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	104
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	105 * mechanical design that supports mounting with the FPC tail folded under the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	106 module, either by way of direct solder termination (no connector) or by way
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	107 of raised sides that create sufficient vertical space to accommodate the FPC
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	108 connector.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	109
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	110 The requirement of 16-bit microprocessor bus interface stems from the desire to
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	111 interface this LCD to the Calypso in exactly the same way how TI did it on the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	112 D-Sample, the 6:00 viewing direction and mechanical mounting requirements stem
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	113 naturally from the target application (cellular phone handset), and the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	114 backlight LED wiring requirement stems from the constraints of our chosen
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	115 MAX1916 backlight LED driver chip - see section 1.4.4.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	116
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	117 1.4.3. Backlight and readability considerations
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	118
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	119 Out of the various pre-existing mobile phones which I (Mychaela) have
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	120 experienced, there have been 3 different kinds of LCDs in terms of how display
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	121 operation and readability interacts with the backlight:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	122
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	123 1) older phones with black&white LCDs: on all phones of this type which I've
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	124 ever used, the display is perfectly readable without the backlight given
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	125 ordinary ambient lighting, be it natural daylight or room lighting. Such
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	126 LCDs are called reflective. With these B&W displays, you only need to turn
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	127 on the backlight if you need to operate the phone in darkness, such as
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	128 outdoors at night or inside with all lights off. The firmware in such phones
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	129 is typically designed to leave the actual display functional and updated at
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	130 all times, with only the backlight subject to on/off control.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	131
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	132 2) most newer phones with color displays, of which Pirelli DP-L10 is a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	133 representative case, have transmissive LCDs that are not designed to be
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	134 readable without the backlight at all - backlight required for readability
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	135 (BLRR) is another way to describe such LCDs. Because the display is not
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	136 readable at all without the backlight, phone firmware is typically designed
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	137 to turn off the entire display (not just the backlight) when the screen goes
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	138 dark, and operation visible to the user is display on/off, rather than
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	139 backlight on/off. It is a good firmware design practice to "swallow" the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	140 initial keypress that turns on the display from dark state, i.e., to block
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	141 the regular action of whatever button was pressed to "wake up" the display.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	142
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	143 3) The color display on Motorola C139 phones is an odd intermediate case: this
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	144 display is NOT practically readable with the backlight off, yet the firmware
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	145 is designed as if the display were readable in this condition: the actual
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	146 display (unsure if it is CSTN or TFT) remains on and updated, and when you
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	147 press some button to "wake up" the display, that button still takes its
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	148 regular action, which is really bad for usability. How do we know that the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	149 actual CSTN or TFT display remains on and actively updated when it is not
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	150 readable with the backlight off? Answer: the non-backlit display can be made
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	151 readable by shining a flashlight directly at it - but this trick requires a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	152 directly pointed flashlight; no amount of ordinary ambient light is enough
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	153 to make the display readable.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	154
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	155 Because our FC Libre Dumbphone handset will have a color display (contemporary
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	156 TFT) and because we are sane, not copying the monumental design mistake of Mot
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	157 C139, our display will fall into class 2 by the above classification: backlight
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	158 required for readability, full display on/off rather than just backlight on/off,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	159 firmware operating like Pirelli's in terms of wake-up keypress swallowing.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	160
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	161 1.4.3.1. Backlight dimming mode
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	162
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	163 Because our LCD is of BLRR type and because we seek to fully replicate Pirelli's
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	164 logic in terms of when keypresses are swallowed and when they are not, we need
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	165 to implement a dimming mode for our LCD backlight. In Pirelli's design which we
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	166 are copying, when you are playing with phone menus or composing SMS etc, but are
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	167 not in an active call, the display switches between full brightness and totally
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	168 off - it goes fully off on timeout, and when you press a button to wake it up,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	169 it switches on at full brightness, together with the keypad backlight. But when
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	170 you are in a call, when the timer expires (and it's a shorter timer, 10 s
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	171 instead of 30 s), the display goes dim instead of fully off, and in this dimmed
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	172 (but still readable) state keypresses are NOT swallowed.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	173
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	174 We only need to implement two different intensity levels for the LCD backlight:
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	175 full brightness and in-call dimmed. The backlight intensity level in the dimmed
43 e1b75668a706 FC-handset-spec: grammar fix Mychaela Falconia <falcon@freecalypso.org> parents: 42 diff changeset	176 state will need to be chosen on this principle: use the lowest backlight LED
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	177 current (to conserve battery power and allow longest talk time on one charge) at
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	178 which the display is still readable, similarly to Pirelli's in-call dimmed
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	179 state.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	180
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	181 In the user-actively-poking state, as opposed to the long-call dimmed state,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	182 there is no need to provide different configurable backlight levels - see
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	183 section 1.4.5.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	184
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	185 1.4.4. Backlight circuit implementation
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	186
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	187 In all candidate TFT LCD modules that are being considered (see section 1.4.2),
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	188 the backlight consists of 3 white LEDs wired in parallel, joined either at the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	189 anode or at the cathode - although as we shall see momentarily, we require an
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	190 LCD module where the 3 LEDs are joined at the anode, with the 3 cathodes brought
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	191 out separately. LCD module datasheets call for 15 mA current through each LED
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	192 at maximum intensity, for 45 mA total, and the LED forward drop voltage (Vf) at
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	193 this rated current seems to range between 2.9 V (what I actually measured on one
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	194 candidate LCD module) to 3.2 V (what the datasheets list as typical) to perhaps
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	195 as high as 3.4 V (what one datasheet lists as the maximum).
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	196
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	197 Given the parallel (as opposed to series) wiring of the 3 LEDs and the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	198 relatively low Vf, there is no need to use any kind of boost converter as part
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	199 of the LED driver circuit for this backlight - any boost converter will only add
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	200 inefficiency (more current will be drawn from the battery for the same LED
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	201 current), hence we need to avoid using such.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	202
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	203 Regardless of whether a given phone design uses a boost converter or not (it
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	204 seems that older designs do use boost converters, either because older white
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	205 LEDs have higher Vf or because 2 or 3 LEDs are wired in series), all traditional
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	206 phone designs seem to share the quality where the display backlight brightness
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	207 remains the same as the battery discharges and as Vbat goes down - this quality
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	208 was directly observed on the Pirelli DP-L10 (unknown circuit design) and
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	209 inferred from the available schematics for Mot C139 and C155, with both of the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	210 latter boost-converting to fixed 5.0 V. In our case, even though we choose to
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	211 not use a boost converter for efficiency reasons, we still need to achieve the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	212 quality of the display brightness remaining the same through the discharge range
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	213 of our Li-ion battery - having the display dim in half as the battery discharges
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	214 from 4.2 V peak to 3.6-3.7 V plateau is simply not acceptable.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	215
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	216 The simplest possible LED driving circuit would be one where a current limiting
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	217 resistor is inserted in series with each LED, and then the 3 parallel
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	218 LED+resistor sets are connected across battery terminals, with a transistor
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	219 inserted somewhere to act as the on/off switch. However, this trivial circuit
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	220 is not suitable in our application because it would produce unacceptably large
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	221 variation in display brightness as the battery discharges - hence we need a more
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	222 intelligent LED driving circuit. Our Luna LCD carrier board from the spring of
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	223 2020 features an LDO bringing Vbat down to fixed 3.5 V, followed by very low-
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	224 value resistors in series with each LED - but this approach is not good for
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	225 production either, as it makes the LED current extremely sensitive to any slight
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	226 variations in Vf.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	227
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	228 Fortunately, I was able to find a specialized white LED driver chip that is just
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	229 perfect for our application, or more precisely, a specialized chip that acts as
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	230 a constant current sink for such LEDs - Maxim MAX1916, design from 2001, just
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	231 the right time frame for the kind of phone we are seeking to build. This
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	232 special chip takes the place of "dumb" ballast resistors: connect Vbat (battery
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	233 positive terminal) directly to the common anode of the 3 LEDs, but instead of
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	234 series resistors, connect each cathode to the corresponding LEDn pin of MAX1916
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	235 - without any resistors or transistors! FETs inside the MAX1916 take the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	236 place of resistors as current-limiting elements, and the chip's global on/off
44 a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	237 control (which will be driven with a Calypso GPIO) takes the place of a separate
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	238 switching transistor.
41 7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	239
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	240 The special quality of MAX1916 is that it produces constant current through each
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	241 LED (based on a set reference current and 230x current multiplication circuit
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	242 inside the chip) regardless of variations in both Vbat and Vf! Of course the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	243 requested current can only be sustained as long as Vbat >= Vf + Vds, where Vds
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	244 is the lowest drop voltage of the FETs inside MAX1916, and once Vbat falls below
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	245 this point, the LED current will begin to decline. However, the beauty of this
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	246 design is that no arbitrary artificial turnover points (like the 3.5 V point in
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	247 our hacky design from the spring of 2020) need to be set: the battery discharge
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	248 point at which the LED current begins to decline will be whatever it comes to be
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	249 naturally, based on Vf (perhaps depending on temperature) and MAX1916 Vds, and
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	250 the decline is expected to be gradual.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	251
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	252 1.4.4.1. Backlight current selection and dimming
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	253
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	254 In the simplest MAX1916-based design, a fixed LED current is set by connecting
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	255 a resistor of appropriately computed value between MAX1916 SET pin and whatever
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	256 regulated fixed voltage rail happens to be available in the system. However,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	257 in our application (see section 1.4.3.1) we need at least two different display
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	258 brightness levels, and thus at least two switchable LED currents. At first the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	259 problem seems difficult, but an elegant solution has been found.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	260
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	261 LCD backlight LED current will be selected by way of two Calypso GPIO pins
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	262 configured as outputs, and a 74LVC2G125 dual tristate buffer. Each tristate
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	263 buffer's A input will be tied high, and the two Calypso GPIO outputs will be
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	264 connected to buffer output enable inputs. There will be two resistors with
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	265 different carefully computed values, each connected between one of the two
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	266 tristate buffer outputs and MAX1916 SET pin. One resistor will provide a small
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	267 current, the other will provide a large current, and each of these two currents
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	268 will be switchable on/off by Calypso GPIO signals switching the buffer outputs
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	269 between driving high (2.7-2.8 V) and Hi-Z. Resistor values will be chosen such
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	270 that the sum of both currents will be the 15 mA limit (the current is reckoned
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	271 per LED), whereas the small current alone will be whatever we need for the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	272 battery-saving long-call dimmed mode.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	273
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	274 1.4.5. Slight regression relative to Pirelli DP-L10
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	275
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	276 The actual LCD backlight LED driving circuit inside the Pirelli phone is not
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	277 known, but reverse engineering of Pirelli's firmware followed by experimentation
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	278 reveals that backlight intensity variation is achieved via a form of PWM, using
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	279 Calypso PWL output - although PWL is used in an inverted sense, such that the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	280 backlight intensity increases with more 0s being put out on PWL, as opposed to
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	281 more 1s. Thus regardless of the unknown actual circuit implementation, the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	282 backlight intensity appears to be continuously variable from 1/255 to 255/255,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	283 which is certainly a much richer control than our crude selection of just 3
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	284 possible LED currents.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	285
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	286 In terms of what Pirelli's fw offers to end users, the backlight intensity in
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	287 the dimmed in-call state is always set to 1/255, without any way to change it,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	288 whereas the backlight intensity in the active interaction state is selectable
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	289 via a menu among 5 levels; the 5 offered levels turn into 1/255, 64/255,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	290 128/255, 192/255 and 255/255 in the resulting PWL programming.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	291
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	292 So in terms of both hardware capabilities and end user offering via the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	293 firmware, Pirelli's LCD backlight level control is richer than what we are
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	294 proposing for our FC Libre Dumbphone. However, engineering is all about
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	295 trade-offs and compromises, and in the Mother's opinion, this slight reduction
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	296 in the richness of functionality is sufficiently offset by the efficiency of
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	297 our MAX1916-based approach: aside from the theoretical possibility of a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	298 switching buck converter, which I've never seen used for LED driving
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	299 applications, our choice of MAX1916 is the most battery-efficient way to drive
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	300 our backlight LEDs. Furthermore, when dimming is effected by switching the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	301 actual regulated LED current, as in our case, as opposed to applying PWM, our
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	302 backlight becomes more resilient to even lower battery voltages.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	303
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	304 Consider what happens when Vbat falls below the point at which the design-
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	305 intended LED current can be maintained - what happens then? If no PWM is
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	306 applied, or if PWM is set to maximum, then display brightness will be whatever
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	307 maximum is possible at this low battery voltage. But if PWM is applied,
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	308 especially very low duty cycles as in the case of Pirelli's dimmed state, then
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	309 the display that has already been dimmed by low Vbat will be further dimmed
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	310 by this aggressive PWM, likely producing an unreadable display at this point.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	311 It may be possible to compensate via extra complexity in the firmware, by
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	312 turning PWM up when Vbat (as measured via Iota MADC) falls too low - but then
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	313 we would be getting really messy, whereas switching the regulated current is so
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	314 much more elegant. With our approach, low-battery-induced dimming in the "full
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	315 brightness" mode will happen at the same discharge point as it would if we had
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	316 used PWM (and set PWM to maximum in this "full brightness" mode), but in the
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	317 in-call dimmed state, further dimming due to low Vbat will probably happen at a
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	318 lower discharge point (if Vf decreases with decreasing current), and when it
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	319 does happen, there won't be a combination of both natural and artificially-
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	320 induced reductions, just the natural one.
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	321
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	322 Thus based on all of the above considerations, I feel justified in my design
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	323 choice of foregoing PWM control of backlight intensity in favor of fixed current
7d77aa76bcaa FC-handset-spec: beginning of massive document Mychaela Falconia <falcon@freecalypso.org> parents: diff changeset	324 switching with much more limited selection.
44 a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	325
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	326 1.5. Main keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	327
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	328 The main keypad on our FC Libre Dumbphone handset will have the following
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	329 21-button arrangement:
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	330
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	331 left soft key ^ right soft key
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	332 <O>
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	333 green call V red power/hang-up
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	334 button button
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	335
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	336 1 2 3
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	337 4 5 6
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	338 7 8 9
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	339 * 0 #
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	340
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	341 The top section above the traditional numeric dial buttons (12) consists of left
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	342 and right soft keys, green and red buttons (classically called SEND/END), and a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	343 5-way navigation button group (left, right, up, down and center), for a total of
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	344 9 buttons in this section. The red hang-up button is also the hardware power-on
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	345 button; having the same button effect power-off when held down for some time is
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	346 a firmware function.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	347
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	348 This 21-button main keypad arrangement is exactly the same as featured on
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	349 Motorola C1xx and Pirelli DP-L10 phones, on TI's D-Sample development platform,
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	350 and also on many other phones (non-Calypso) from the appropriate era, such as
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	351 Samsung E2232.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	352
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	353 1.5.1. Keypad backlight
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	354
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	355 All traditional phones including Mot C1xx and Pirelli DP-L10 feature keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	356 backlights, hence we need to include one as well. The exact structure of this
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	357 backlight won't be known until we enter the mechanical design phase for the
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	358 actual handset (as opposed to intermediate development boards), which will be
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	359 much later in the project, but the Mother's understanding is that keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	360 backlights are made up of some number of LEDs (2 on Pirelli DP-L10, unknown
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	361 number on Mot C139) and some kind of light diffuser.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	362
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	363 Given the discovery of MAX1916 constant-current-sink LED driver chip (see
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	364 section 1.4.4), the optimal electrical design of the keypad backlight becomes
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	365 clear: use 3 LEDs, and drive them using another MAX1916 chip, separate from the
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	366 one used for the LCD backlight.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	367
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	368 Backlight intensity: neither Mot C139 nor Pirelli DP-L10 provides any way to
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	369 vary keypad backlight intensity, and no such variability is deemed necessary.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	370 In the long-call state when the LCD backlight is dimmed, the keypad backlight
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	371 is fully off. We shall use a fixed LED current setting for our keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	372 backlight, set with a single fixed resistor between the keypad MAX1916 chip's
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	373 SET pin and the V-IO rail, and the actual current value will be determined in a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	374 much later phase of the project, when we have the actual keypad backlight LEDs
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	375 and a better idea of the mechanical design.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	376
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	377 Backlight color: Mot C139 uses blue LEDs, Pirelli DP-L10 uses white LEDs.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	378 Because blue and white LEDs have very similar electrical characteristics
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	379 (current needed for appropriate brightness, Vf at this current), the choice
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	380 between the two can be made in a much later project phase, based on input from
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	381 other team members who are better at aesthetics.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	382
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	383 1.5.1.1. Comparison with Mot C139 and Pirelli DP-L10
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	384
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	385 Both of these two pre-existing reference phones feature keypad backlights that
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	386 are switched on/off via Iota LEDB; the actual circuit design is unknown.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	387 However, in our design we forego Iota LEDB altogether (it won't be used for
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	388 anything), and use two MAX1916 chips for our LCD and keypad backlights, with
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	389 each chip's on/off control being a Calypso GPIO.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	390
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	391 The actual workings of the LEDB driver or switch inside the Iota chip are a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	392 mystery. On the one hand it appears to be nothing more than a "dumb" transistor
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	393 on/off switch, no different from an external "digital transistor" (BJT with bias
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	394 resistors) controlled by a Calypso GPIO: a resistor still seems to be required
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	395 for current control, and at least on the Pirelli DP-L10 the keypad backlight
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	396 intensity visibly varies with Vbat ranging over the Li-ion discharge range. But
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	397 on the other hand, LEDB requires the 13 MHz clock to be running, and the light
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	398 goes out when this clock is stopped. Why in the world would any kind of clock
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	399 be required if the circuit is only a transistor on/off switch controlled by a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	400 static register bit? Other parts of TI's Iota datasheet describe its LEDA, LEDB
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	401 and LEDC as "current drivers" - but in the absence of any way to actually set
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	402 the desired current without depending on Vbat or Vf variations, whatever the
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	403 Iota chip actually provides can't be anything like MAX1916.
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	404
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	405 Poorly documented, non-understood mystery hardware is best avoided, hence we are
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	406 not going to use Iota LEDB, and shall only use MAX1916 instead. We also gain a
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	407 functional improvement over Pirelli DP-L10 by using MAX1916: our keypad
a415ae467c6d FC-handset-spec: main keypad and its backlight documented Mychaela Falconia <falcon@freecalypso.org> parents: 43 diff changeset	408 backlight intensity will remain the same over the battery discharge range.
45 9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	409
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	410 1.6. Side buttons
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	411
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	412 In addition to the 21-button main keypad, our FC Libre Dumbphone handset will
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	413 include 3 side buttons: two on the left side, intended for volume up/down
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	414 control, and one on the right side, serving auxiliary functions. This side
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	415 button arrangement is identical to TI's D-Sample and similar to Pirelli DP-L10:
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	416 the only difference between our arrangement (matching D-Sample) and Pirelli's
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	417 is that Pirelli moved the 3rd side button to the left and designated it as the
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	418 camera button. However, we (FreeCalypso) have no interest in ever implementing
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	419 any kind of camera on our phones, hence we are moving the 3rd side button back
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	420 to where it was in TI's original design (on the right), and we will use it for
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	421 purposes of our own invention.
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	422
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	423 The starting point UI code we got from TI does not do anything with the right
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	424 side button (even though this button exists and works on the D-Sample platform
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	425 on which this code was originally developed), hence we have full freedom to
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	426 invent our own uses for it. The following uses are envisioned:
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	427
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	428 * Long press of this button may be our way of turning the hands-free loudspeaker
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	429 on and off, a function that does not exist in the starting point UI code from
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	430 TI.
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	431
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	432 * When the phone is in its normal idle standby operation (not in a call and not
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	433 being poked at by the user, but registered to a GSM network and ready to
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	434 accept incoming calls or SMS), the display will be off. Users often desire
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	435 to check the time and other status (check coverage, see if they missed any
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	436 calls or SMS), which will require pressing any button to turn on the display.
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	437 At that point a 30 s timer kicks in, which will turn the display back off
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	438 after 30 s of inactivity. However, an argument can be made that keeping the
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	439 display on for 30 s if the user only wanted to quickly glance at the time is
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	440 a waste of battery. Here is one proposed solution: we can implement a
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	441 function where a short press of the right side button when the phone is on its
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	442 idle screen will cause the display to turn off immediately and activate the
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	443 keyguard. The user can then press the right side button once to turn on the
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	444 display and look at it, and then press the same button again to turn it back
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	445 off.
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	446
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	447 * When we are in a long call, the LCD backlight does not turn off completely,
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	448 instead it will go dim - but still readable. Any button presses in this state
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	449 are NOT swallowed - they take their regular actions. However, the keypad
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	450 backlight turns off fully in this state, and under certain conditions (like
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	451 out at night) the user may not be able to see the keypad. If a short press
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	452 of the right side button invokes no other action besides switching on full
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	453 display brightness and the keypad backlight, this right side button can be
9df8683daec4 FC-handset-spec: side buttons documented Mychaela Falconia <falcon@freecalypso.org> parents: 44 diff changeset	454 found by touch, and thus solve this particular problem case.
46 1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	455
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	456 1.7. Audio routing
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	457
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	458 3 different audio routing modes will be supported on our FC Libre Dumbphone
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	459 handset:
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	460
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	461 * Default mode: there will be a 32 ohm earpiece speaker physically mounted in
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	462 the usual place, on the front bezel above the display, to match up with the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	463 user's ear in handheld operation. There will also be a microphone toward the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	464 front bottom of the phone, again in the usual place.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	465
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	466 * Hands-free mode: there will be an 8 ohm loudspeaker physically separate from
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	467 the 32 ohm earpiece speaker, physical location in the handset TBD. In the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	468 hands-free mode, the downlink audio will be switched from the earpiece speaker
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	469 to the loudspeaker, while the microphone input for the uplink will remain the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	470 same.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	471
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	472 * There will be a wired analog headset jack with plug insertion detection; when
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	473 a headset is inserted, both audio input and output will be redirected to this
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	474 headset interface.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	475
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	476 1.7.1. Earpiece and loudspeaker separation
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	477
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	478 Most current mainstream phones (in fact, all that I am familiar with) have
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	479 physically separate speaker transducers for the earpiece function (hold up to
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	480 ear to talk) and the loudspeaker+ringer function. The earpiece speaker is a 32
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	481 ohm load, and the loudspeaker is an 8 ohm load. In a Calypso+Iota design, an
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	482 external amplifier chip is needed to drive the 8 ohm loudspeaker, whereas the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	483 little 32 ohm earpiece speaker can be driven directly by Iota EAR output.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	484
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	485 However, a very different design was implemented by TI on their D-Sample and
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	486 Leonardo boards. They have only one speaker, one of 8 ohm kind, that is
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	487 physically mounted in the position where the earpiece speaker would normally go.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	488 In order to not overwhelm the user's ear in handheld operation, they have
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	489 peculiar circuit wiring where the analog signal from Iota to the loudspeaker
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	490 amplifier goes through different resistor values depending on whether EAR or AUX
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	491 output from Iota is used, and when the EAR output is selected, the high resistor
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	492 values produce attenuation, such that the sound pressure level produced by the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	493 pressed-to-ear loudspeaker becomes comparable to that produced by a more
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	494 traditional 32 ohm earpiece speaker.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	495
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	496 Furthermore, TI's single speaker design was not limited to their development
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	497 boards. Some years ago I found schematics for some very old LG phone (called
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	498 A316 or B1200, not sure of the correct designation), this phone is from early
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	499 TI era (pre-Calypso, using Ulysse/Nausica/Clara chipset), and it has the same
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	500 arrangement as D-Sample and Leonardo.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	501
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	502 For our own FC Libre Dumbphone, I am going with the separate speakers
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	503 architecture, using physically separate earpiece and loudspeaker transducers.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	504 This architecture feels more native to me, and it will allow for independent
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	505 tuning of the two audio paths. In my defense, all current mainstream phones
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	506 seem to use the same architecture - the other approach with a single loudspeaker
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	507 in the earpiece physical position seems very uncommon.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	508
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	509 1.7.2. Loudspeaker implementation
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	510
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	511 The external amplifier chip for driving the 8 ohm loudspeaker will be TI
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	512 TPA6203A1, copied from Leonardo schematics and proven good on FCDEV3B. On
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	513 FCDEV3B this amplifier is fed with signal from Iota EAR output, but on the final
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	514 handset and on the Venus development board this amplifier will be fed with
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	515 signal from Iota AUX output instead.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	516
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	517 The loudspeaker amplifier has an on/off control by way of a Calypso GPIO; in
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	518 order to save battery, this amplifier needs to be off normally, and only turn on
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	519 when a loudspeaker call is in progress or when a ringtone melody is played.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	520
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	521 1.7.3. Wired analog headset jack
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	522
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	523 The analog headset jack on our FC Libre Dumbphone handset will be of 2.5 mm
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	524 TRRS type, using pinout copied from iWOW DSK. The headset needs to be wired as
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	525 follows:
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	526
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	527 * 32 ohm earpiece speaker connected between Tip and Ring2;
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	528 * electret condenser microphone, positive connected to Ring1;
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	529 * Sleeve is ground, should be needed only for the microphone.
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	530
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	531 The advantage of this TRRS headset specification, as opposed to the simpler kind
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	532 with a TRS plug and a common ground for the earpiece and the mic, is that our
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	533 TRRS headset can be driven with either single-ended or differential earpiece
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	534 driver outputs. On the final handset, the wired headset interface will be
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	535 connected to the Iota headset channel (HSMICBIAS, HSMICP, HSO) and thus the
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	536 headset earpiece driver will be single-ended (HSO and GND), but the same headset
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	537 can also be plugged into other FreeCalypso devices in which the jack is wired
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	538 to the main Iota audio channel, with Iota EARP & EARN driving Tip and Ring2 on
1fec0a3f09cc FC-handset-spec: audio routing documented Mychaela Falconia <falcon@freecalypso.org> parents: 45 diff changeset	539 the TRRS headset jack.
47 f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	540
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	541 1.8. Ringtone generation
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	542
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	543 In terms of the physical sound-emitting element, there are two principal ways
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	544 in which cellphone ringing sounds can be produced:
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	545
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	546 1) The oldest and most classic way is to use a magnetic buzzer controlled by
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	547 Calypso BU/PWT digital output. The buzzer is driven with raw battery voltage
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	548 being switched with a "digital transistor" (BJT with bias resistors), and the
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	549 control input going to the base of the BJT is Calypso BU/PWT output. This
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	550 method is standard in older phones that don't have hands-free loudspeakers:
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	551 since there is no loudspeaker for that other purpose, some loud noise-making
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	552 element needs to be implemented just for ringing, and old-style buzzers are
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	553 the traditional choice. Motorola C1xx lower subfamilies (C11x/12x and
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	554 C139/140) use such buzzers for ringing.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	555
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	556 2) In phones that feature a loudspeaker for hands-free operation, the same
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	557 loudspeaker is also used for ringtone sounding, and the buzzer is eliminated.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	558 Apparently hands-free loudspeakers weren't popular in the Calypso era, thus
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	559 Pirelli DP-L10 is the only known Calypso phone that features one. There is
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	560 also a more bizarre possibility: some phones have replaced the ringing buzzer
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	561 with a loudspeaker, but that speaker is used only for playing ringtone
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	562 melodies - no hands-free call feature is offered. This situation exists on
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	563 Motorola C155/156 phones.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	564
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	565 Furthermore, if the physical sound-emitting element is a loudspeaker and not an
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	566 old-fashioned buzzer, and if the chipset is Calypso, as opposed to various newer
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	567 chipsets, then a further distinction arises:
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	568
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	569 2a) Most historical commercial phones that are based on Calypso and use a
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	570 loudspeaker for ringtone sounding, also contain a special ringtone generator
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	571 chip that drives this speaker when a ringtone is played - in other words,
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	572 their loudspeaker ringtones do NOT go through the same voice audio path that
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	573 is used for hands-free calls, if the latter feature is offered at all. The
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	574 speciai ringtone generator chip is typically a combined MIDI player and
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	575 loudspeaker driver.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	576
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	577 2b) The much less popular approach is to not implement any extra hardware at all
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	578 that is specifically for ringtone generation, use only the same loudspeaker
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	579 audio path hardware that is already needed for hands-free calls (a simple
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	580 loudspeaker amplifier), generate ringtone melodies in the Calypso DSP
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	581 (Melody E1 or E2), and play them through the regular voice audio path,
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	582 routed to the loudspeaker.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	583
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	584 Approach 2b is the least popular one among historical commercial Calypso phones,
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	585 but it is the one which I (Mother Mychaela) have selected for our FC Libre
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	586 Dumbphone handset. But let us nonetheless examine the pros and cons of
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	587 different approaches, and see why I have settled on option 2b.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	588
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	589 Buzzer melodies (option 1) are monophonic (the signal carrying the melody to
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	590 the buzzer is a digital square wave, and there is no way to create multiple
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	591 overlapping notes in such a signal), but a decent range of tone frequencies is
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	592 available: the magnetic buzzer hardware can easily produce frequencies all the
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	593 way up to the limit of human hearing, while Calypso PWT produces musical notes
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	594 from F4 through E8 in the scientific pitch notation, or 349 to 5274 Hz. In
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	595 contrast, any tones produced through the 8000 samples/s voice audio path have
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	596 to be below the Nyquist frequency of 4 kHz - according to TI's document, Melody
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	597 E1 notes go from E4 (330 Hz) up to G#7 or 3322 Hz.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	598
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	599 In terms of the richness of possible ringtone melodies that can be played,
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	600 option 2a (external MIDI player chip that drives the loudspeaker directly,
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	601 without going through Calypso+Iota voice audio path) is the absolute best.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	602 These specialized ringtone generator chips implement full MIDI (128 instruments,
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	603 47 drums, up to 64 simultaneous notes, according to one datasheet), and the
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	604 available ringtone melodies for these MIDI chips are very rich - just take a
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	605 Pirelli DP-L10 phone and listen through various ringtone melodies it offers.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	606 All of Pirelli's melodies are stored as *.mid files in their FFS, thus we could
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	607 very easily copy them if we were to adopt a MIDI player chip similar to theirs.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	608
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	609 However, the problem for us with adopting option 2a is that this option would
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	610 introduce significant extra complexity and adversely affect our already long-
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	611 overdue project schedule. There is only one MIDI ringtone player chip for which
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	612 we have enough documentation to attempt such a feat: this chip is Winbond
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	613 W56964, a slightly more capable sibling of the W56940 used in the Pirelli phone.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	614 However, just because we have what at first glance appears to be reasonably
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	615 complete documentation does not mean that it would be a slam dunk! We would
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	616 have to build a separate test board for this chip, connect it to a Caramel2
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	617 motherboard (it needs to connect to Calypso MEMIF), and then spend significant
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	618 time climbing the learning curve and getting this chip to actually work: getting
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	619 it to play melodies, and just as important, getting it into and out of sleep
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	620 modes. In other words, a lot of extra work and time spent just for this part,
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	621 not advancing any other project needs - whereas option 2b eliminates all of this
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	622 extra work.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	623
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	624 Finally, a philosophical argument can be made that FreeCalypso should be all
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	625 about simplicity, producing a phone that does its job: implement just what is
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	626 needed for a functional phone, and omit unnecessary baggage. An extra hardware
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	627 circuit (a chip connected to Calypso memory bus, no less) and associated
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	628 software complexity that serves absolutely no other purpose except to produce
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	629 ringtones that are "richer" than what the Calypso can produce on its own, and
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	630 does not assist in any way with hands-free loudspeaker operation for calls (it
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	631 is more of a hindrance in that mode), can be seen as an unwelcome burden similar
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	632 to other unwelcome burdens which we are already eliminating, like the camera.
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	633
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	634 In contrast, with our chosen option 2b, we have exactly zero extra hardware
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	635 that is just for ringing: our loudspeaker and its associated driver circuit
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	636 (simple amplifier) is primarily for hands-free calls, and the ability to use
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	637 the same audio path to play ringtone melodies comes literally "for free" with
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	638 the Melody E1 feature built into our Calypso DSP. We already have a selection
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	639 of nice-sounding ringtone melodies in E1 format, lifted from the legendary TSM30
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	640 source, and software complexity is minimal: the melody playing engine has
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	641 already been implemented by TI, we only need to call RiViera Audio Service API
f0419ac0a815 FC-handset-spec: ringtone generation documented Mychaela Falconia <falcon@freecalypso.org> parents: 46 diff changeset	642 functions.
48 cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	643
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	644 1.9. Vibrator
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	645
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	646 All traditional cellphones include a vibrator, and ours needs to include one
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	647 too. Our firmware will need to offer the options of being silent, vibrating
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	648 only, ringing only, or ringing and vibrating on an incoming call or SMS - all
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	649 of these options are genuinely useful to a heavy-duty phone user in different
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	650 situations.
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	651
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	652 In terms of functionality, the vibrator is envisioned as a simple on/off control
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	653 in the hardware, with higher-level "pulse train" functionality implemented in
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	654 the firmware. As far as end user experience goes, the Mother's plan is to copy
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	655 the way the vibrator works on the Pirelli DP-L10. On this to-be-replaced or
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	656 to-be-recreated reference phone, the vibrator works as follows: when an incoming
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	657 call arrives in vibrating alert mode, the firmware turns the vibrator on for
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	658 500 ms, then turns it off for 500 ms, and the cycle endlessly repeats until the
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	659 call is either answered or dropped. This 500 ms on/off cycling is purely a
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	660 firmware function, the hardware control is an on/off switch.
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	661
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	662 Looking at the hardware implementation of the vibrator driving circuit in the
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	663 Motorola C1xx family and in the Pirelli DP-L10, both designs support a form of
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	664 "analog" control of the vibrator beyond simple on/off. In the Mot C1xx family
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	665 the vibrator is controlled by the output of Iota auxiliary DAC, whereas in the
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	666 Pirelli DP-L10 Calypso BU output has been repurposed to control the vibrator,
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	667 allowing either full-on or PWM driving. However, Pirelli's firmware appears to
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	668 never operate the vibrator in any way other than fully on, and there is no
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	669 evidence of Mot C1xx firmwares applying any analog control to their vibrator
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	670 either.
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	671
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	672 The Mother's tentative plan for our FC Libre Dumbphone handset is to copy
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	673 Pirelli's approach in both hardware and firmware: repurpose Calypso BU output
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	674 for vibrator control (we won't have a buzzer, see section 1.8), allowing the
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	675 possibility of PWM, but have our firmware only use fully-on and fully-off
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	676 states, at least initially. However, because we won't have a vibrator on our
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	677 Venus development board, only in the final handset, this decision does not have
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	678 to be made right now.
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	679
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	680 Because our firmware will be designed for a simple on/off vibrator control,
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	681 during fw development on the Venus board it will be trivial to use a LED to
cb8d43a5023c FC-handset-spec: vibrator documented Mychaela Falconia <falcon@freecalypso.org> parents: 47 diff changeset	682 simulate the vibrator on/off state.
49 38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	683
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	684 1.10. Battery
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	685
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	686 The battery in our FC Libre Dumbphone handset will be single-cell Li-ion. It
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	687 goes without saying that this battery will be freely removable and replaceable
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	688 by end users. The specific size, form factor and mAh capacity of this battery
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	689 won't be addressed until later in the project, when we get closer to building
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	690 the actual handset.
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	691
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	692 Our Calypso+Iota chipset dates from the era when the cellular handset industry
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	693 was transitioning from NiMH to Li-ion batteries, and the Battery Charger
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	694 Interface (BCI) block in the Iota chip supports both battery types, or at least
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	695 TI's documentation claims so. Given that we are going against the mainstream
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	696 society's ideas in so many other ways, I have given thought to the possibility
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	697 of using a NiMH battery instead of Li-ion. However, the problem with using a
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	698 NiMH battery is that we would be going into completely uncharted territory
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	699 without any guidance. In the case of Li-ion batteries the charging process is
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	700 well-understood in both theory and practice, and our FCHG logic based on reverse
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	701 engineering of Pirelli's firmware works well both on the same Pirelli and on
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	702 Motorola C1xx family. In contrast, if we went with NiMH, we would have
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	703 absolutely no guidance in implementing the necessary charging control logic
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	704 (TI's LCC code is useless), causing a huge risk to the project. Furthermore,
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	705 determining the state of charge from Vbat for the purpose of the bars icon is
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	706 already somewhat challenging even with Li-ion, given the relatively flat middle
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	707 part of the discharge curve - and with NiMH we can only expect the problem to be
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	708 even worse, as their discharge curve is said to be even flatter. For these
38bcb9425df0 FC-handset-state: battery documented Mychaela Falconia <falcon@freecalypso.org> parents: 48 diff changeset	709 reasons, we are going to play it safe and stick with Li-ion.
50 da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	710
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	711 1.11. Charging circuit
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	712
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	713 Our FC Libre Dumbphone will feature a USB port (mini-B, device role only, no
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	714 OTG) that combines two logically separate functions: battery charging and
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	715 computer interface. The basic idea of this dual-function USB port comes from
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	716 Pirelli DP-L10, but we are applying significant refinements of our own to this
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	717 general idea, as the following description will make clear. This section
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	718 describes the charging function; the computer interface function is described
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	719 in section 1.12.
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	720
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	721 One highly non-standard innovation that will appear on our FC handset will be a
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	722 user-visible mechanical slide switch that will turn the charging circuit on or
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	723 off. The purpose of this charging on/off switch is to make it possible to
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	724 connect USB and have the two ttyUSB devices appear (see section 1.12) without
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	725 presenting a 'charger plug' boot condition to the Calypso+Iota core chipset.
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	726 From an end user perspective, if you only use the USB port for charging and
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	727 don't care about the computer interface function, then leave the charging switch
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	728 always on - USB plug/unplug will mean charger plug/unplug like on any
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	729 conventional phone. Similarly, if you do use the computer interface function to
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	730 connect your phone to a host computer in regular operation, with the firmware
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	731 up and running normally, but you don't mind having the phone also charge from
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	732 your computer every time you connect USB, then likewise leave the charging
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	733 switch always on. However, if you are going to reflash phone firmware or do
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	734 other advanced manipulations using the computer interface, then you will need
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	735 to turn the charging switch off. With the switch off, the USB port becomes a
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	736 computer interface only, without charging.
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	737
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	738 Past the switch, the battery charging circuit using USB +5V as the charging
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	739 power source will be the most classic one depicted in Figure 4-10 in the Iota
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	740 chip datasheet (TWL3025_SWRS021.pdf), same as in Pirelli DP-L10 and Motorola
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	741 C1xx phones. Presentation of USB +5V to Iota VCHG terminal past the charging
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	742 on/off switch is what will cause the chipset to boot in the 'charger plug' mode,
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	743 or to activate charging functions in the firmware if the phone is already on.
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	744
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	745 1.12. Computer interface
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	746
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	747 Our Calypso chip has no native USB, instead the host computer interface of all
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	748 Calypso-based systems consists of two UARTs. On our development boards starting
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	749 with FCDEV3B, we got used to interfacing to both of these UARTs by way of
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	750 FT2232x adapters, a USB to serial adapter that goes from one USB device to two
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	751 UARTs, presenting two ttyUSB devices to a Linux host. For low-level operations
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	752 like flash programming, having just one Calypso UART is sufficient (either of
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	753 the two), but once our regular firmware is up and running, then having both
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	754 Calypso UARTs gives maximum user empowerment: Modem UART carries a classic AT
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	755 command interface complete with CSD, GPRS and GSM 07.10 MUX capabilities, while
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	756 the other UART (IrDA) carries TI's RVTMUX debug and development interface.
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	757
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	758 Before arriving at our current radical approach with the charging on/off switch,
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	759 for many years previously I was considering a more conservative approach. My
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	760 original idea was to bring out the two Calypso UARTs in very different ways: my
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	761 thought was to bring only the Modem UART to the built-in USB port (by way of a
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	762 built-in single-channel USB-serial chip), and have plugged-in USB always present
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	763 VCHG to the chipset, but route the debug UART (the one most useful in low-level
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	764 development and bring-up) to a special FPC connector that would interface to a
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	765 special debug board, just like Openmoko did on their Neo. Serious development
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	766 work would then require having that debug board attached, while more casual
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	767 users would be able to talk AT commands to the phone via the built-in USB port,
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	768 charging the battery at the same time.
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	769
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	770 What made me change my mind about this design was the realization that I, as the
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	771 most principal user and developer, would end up wanting to have the debug board
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	772 attached all the time, and the need to have it hanging externally, or perhaps
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	773 glued or taped to the back of the phone, would be a huge blemish and
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	774 inconvenience. Back in the days of Openmoko, someone must have had a similar
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	775 experience, as I remember reading about a hack where someone built a debug board
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	776 functional equivalent that fits inside the Neo, in some otherwise unused space.
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	777
da1a2a32c260 FC-handset-spec: USB description started Mychaela Falconia <falcon@freecalypso.org> parents: 49 diff changeset	778 Hence the new design for our planned FC Libre Dumbphone handset: the USB port
51 7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	779 will have a built-in FT2232D (or perhaps FT2232H) subsystem (USB to two UARTs)
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	780 connected to it, interfacing to both Calypso UARTs, while the charging on/off
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	781 switch will make it possible to use this interface for low-level development
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	782 and bring-up without presenting VCHG to the chipset. In this architecture this
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	783 FT2232x subsystem should be considered the primary "owner" of the handset's USB
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	784 port, while the charging function is secondary and optional, enabled or disabled
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	785 with a switch. To put it another way, if our USB port is connected to a regular
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	786 USB host (as opposed to a Dedicated Charging Port power-only source), that USB
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	787 host will always enumerate the FT2232x and see two ttyUSB devices, whereas
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	788 charging may or may not take place depending on the switch setting.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	789
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	790 1.12.1. Set of UART signals
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	791
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	792 The set of signals to be connected between Calypso and FT2232x for the Modem
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	793 UART is almost complete:
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	794
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	795 USB UART
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	796 DTE signal Calypso signal
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	797 ------------------------------
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	798 TxD RX_MODEM
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	799 RxD TX_MODEM
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	800 RTS CTS_MODEM
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	801 CTS RTS_MODEM
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	802 DTR GPIO3
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	803 DCD GPIO2
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	804 RI GPIO8
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	805
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	806 Only DSR is omitted for the Modem UART channel, all others are included. The
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	807 second debug UART channel is only two wires:
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	808
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	809 USB UART
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	810 DTE signal Calypso signal
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	811 ------------------------------
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	812 TxD RX_IRDA
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	813 RxD TX_IRDA
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	814
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	815 However, as shown in the next section, these signals cannot be simply connected
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	816 between Calypso and FT2232x, and a more complicated scheme needs to be
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	817 implemented instead.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	818
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	819 1.12.2. USB and mobile power domains
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	820
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	821 Our FC Libre Dumbphone handset will have two principal power domains in it: the
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	822 main battery-powered mobile domain, and the USB domain. This power domain
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	823 situation presents some very significant challenges, a problem generally
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	824 referred to as "partial power-down". There are two PPD scenarios to be
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	825 concerned about:
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	826
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	827 1) In normal operation the phone is mobile and not connected to USB. In this
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	828 state the mobile power domain is on, whereas USB-powered circuits in the
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	829 FT2232x subsystem have no power. The two challenges in this state are:
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	830
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	831 1a) We need to ensure that no currents flow from the powered-on mobile domain
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	832 into powered-down USB domain circuits, as any such currents would be an
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	833 unacceptable drain on the battery.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	834
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	835 1b) Calypso UART inputs that come from the USB domain when the latter is active
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	836 need to have defined logic levels on them when the USB domain has no power:
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	837 no floating, no mid-way levels that would cause higher currents in CMOS
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	838 input structures, and furthermore, some Calypso inputs need to be high in
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	839 this state, while others need to be low.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	840
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	841 2) A reverse PPD scenario occurs when the USB domain has power, but the
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	842 Calypso+Iota chipset is in its switched-off state per Iota VRPC. This
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	843 scenario can occur when the charging switch is set to off, or when the
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	844 battery is critically low and undergoing precharge. The main concern in
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	845 this state is to avoid feeding power from the USB domain into the Calypso
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	846 chipset's V-IO rail - our experience on Caramel2 boards conclusively
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	847 demonstrates that Calypso does not like this condition and can behave oddly,
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	848 erratically feeding current into its outputs that are supposed to be low or
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	849 Hi-Z, and thereby erratically turning on various peripherals.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	850
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	851 If we were to naively connect our UART signals between Calypso and FT2232x, the
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	852 result would be bad: all of the above concerns would be violated. Instead we
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	853 need to insert carefully designed isolating buffer circuits in both directions.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	854
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	855 1.12.2.1. Calypso to FT2232x signal direction
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	856
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	857 If these signals were connected directly, significant current (in the mA range)
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	858 would flow from Calypso outputs into powered-down FT2232x inputs, which is not
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	859 acceptable. Our solution is to insert an LVC buffer (probably 74LVC541A, for
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	860 the 5 signals that are needed) between Calypso outputs and FT2232x inputs, with
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	861 the buffer powered from USB domain 3.3V supply. With mobile on and USB power
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	862 absent, the LVC buffer's Ioff spec will apply, which is listed in Nexperia's
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	863 74LVC541A datasheet as 0.1 uA typical, 10 uA maximum.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	864
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	865 An unfortunate consequence of this design is that in the opposite PPD scenario
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	866 (USB connected to a host, charging switch off, mobile chipset in its off state)
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	867 the inputs to the LVC buffer will float, with FT2232x inputs receiving garbage
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	868 as a result. Adding pull-up resistors to a USB-domain supply would cause other
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	869 problems, hence the Mother's position is that we'll just live with a few
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	870 floating inputs in this particular condition - and it is a condition that
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	871 should not persist for extended lengths of time. There is also a software
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	872 consideration stemming from this floating input situation: when you are doing
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	873 low-level programming and development operations in this state, don't open the
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	874 Modem UART ttyUSB device, and only operate via the other debug UART. The latter
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	875 is a 2-wire UART without any flow control or modem control signals, hence there
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	876 will be less bogosity for the Linux host to see in this state.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	877
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	878 1.12.2.2. FT2232x to Calypso signal direction
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	879
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	880 This direction is even more difficult, and we will need to insert two chained
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	881 LVC buffers: the signals will first pass through an LVC buffer powered from the
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	882 USB domain, and then through another LVC buffer powered from the Calypso+Iota
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	883 chipset's V-IO rail. There will be pull resistors inserted between the two
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	884 buffers: either pull-up to VBAT (raw battery positive rail) or pull-down to GND,
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	885 depending on the needed signal sense.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	886
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	887 The LVC buffer powered from Calypso V-IO is needed in order to prevent current
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	888 feeding into Calypso when the mobile is switched off - the buffer's Ioff spec
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	889 will apply. Pull-up and pull-down resistors in front of this buffer are needed
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	890 so that Calypso inputs will receive the desired states when no USB host is
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	891 connected. Pull-ups are being made to VBAT instead of V-IO to eliminate the
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	892 possibility of current feeding into V-IO through these resistors. (Feeding
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	893 from 3.3V logic signals into the battery can't happen when the battery is above
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	894 3.3 V, and if the battery is below 3.3 V, then we are only adding a little to
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	895 the precharge current.)
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	896
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	897 The other LVC buffer (the one powered from USB-domain 3.3V) is needed because
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	898 in the absence of this buffer, current will flow through pull-up resistors and
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	899 into powered-down FT2232x output pins, the resulting pull-down resistance will
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	900 be lower than the pull-up, and the next buffer won't receive the desired logic
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	901 level, not to mention unwanted current flowing. With the other LVC buffer
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	902 added, that buffer's Ioff spec will apply.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	903
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	904 The value of pull-up resistors to VBAT will be 22 kOhm. With maximum 15 uA
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	905 current flowing through each resistor (worst-case Ioff of one buffer plus
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	906 worst-case Ii of the other buffer), the maximum voltage drop on the 22 kOhm
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	907 resistor will be 330 mV. In order for the LVC buffer's input structure to not
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	908 draw extra current, the input voltage needs to be 2.8 V or higher - thus with
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	909 22 kOhm resistors we'll keep satisfying this condition until the battery falls
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	910 to about 3.1 V, which is below the operational range for switched-on mobile.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	911
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	912 One downside of having pull-ups to VBAT (which can be as high as 4.2 V) on
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	913 signals that are output from a 3.3V-powered buffer is that when the buffer
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	914 output is high, there may be current flowing into that high output (not sourcing
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	915 out of it as normally expected), which is a bad condition for CMOS outputs.
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	916 However, this current will be limited to a maximum of about 40 uA
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	917 ((4.2-3.3 V) / 22 kOhm), and my feeling is that such small current won't hurt
7933c3a1b5e0 FC-handset-spec: power domain mess documented Mychaela Falconia <falcon@freecalypso.org> parents: 50 diff changeset	918 Nexperia LVC buffers.

FreeCalypso > hg > freecalypso-docs

annotate FC-handset-spec @ 51:7933c3a1b5e0