FreeCalypso > hg > freecalypso-tools

annotate doc/Deep-sleep-support @ 788:f3fc782b5e88

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
CHANGES: post-r14 begins with simagent
author Mychaela Falconia <falcon@freecalypso.org>
date Sun, 14 Mar 2021 00:07:25 +0000
parents 19cabe7c8e08
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
427
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
1 All standard phones and modems based on the Calypso chipset from TI implement
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
2 several different power saving modes, called sleep modes, and one of these sleep
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
3 modes has a profound impact on the operation of the externally visible UART
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
4 interfaces provided by the device. The power saving mode in question is called
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
5 deep sleep, and the phone or modem can only enter this deep sleep mode when it
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
6 is in the so-called idle state, meaning that it is camped on a cell and is ready
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
7 to receive incoming calls, messages or GPRS packets - deep sleep cannot be
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
8 entered while in an active call or in the middle of packet data transfer. When
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
9 a Calypso GSM device is idle with deep sleep enabled, it will only wake up at
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
10 preprogrammed intervals to listen on the paging channel, and will stay in deep
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
11 sleep in between these paging windows. Calypso GSM devices also enter deep
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
12 sleep when they are completely idle with no radio network connection.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
13
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
14 When a Calypso GSM device enters deep sleep, the main VCXO or VCTCXO that runs
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
15 at 13 or 26 MHz and provides all other clocks in normal operation is completely
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
16 stopped (powered off), and the only clock that remains running is the 32.768 kHz
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
17 watch crystal oscillator. The preprogrammed wakeup timing (waking up to listen
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
18 on the paging channel at the right time) is driven by this 32.768 kHz clock, but
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
19 the Calypso can also be woken up ahead of the programmed time by an external
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
20 interrupt such as a button press on the phone keypad.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
21
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
22 This deep sleep mode provides a very important power saving measure (the
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
23 extremely low current draw that is achieved during deep sleep is not possible
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
24 without stopping the fast clock), but it presents a real challenge for the
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
25 external UART interfaces. Consider what happens when an external host sends
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
26 some characters to one of Calypso's UARTs (either the AT command interface or
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
27 RVTMUX) while the GSM device is in deep sleep. In normal operation a UART
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
28 requires a clock of 16x the baud rate (some vendors' UARTs can make do with
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
29 only 8x the baud rate) in order to receive asynchronous incoming characters,
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
30 and in the Calypso these UART clocks come from the 13 MHz master clock - but
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
31 that master clock is stopped during deep sleep!
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
32
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
33 Calypso UARTs have some special asynchronous (non-clock-dependent) logic that
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
34 causes a wakeup signal to be generated if some incoming traffic is detected at
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
35 a UART while in deep sleep, but the first character that triggers this wakeup
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
36 will be lost: the asynchronous logic can detect that there is "something
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
37 happening" on the UART RxD line, but it cannot catch the actual byte content
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
38 without a clock: the *only* clock available during deep sleep is 32.768 kHz,
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
39 and even at 9600 baud one would need a clock several times faster than this
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
40 rate in order to receive and register an incoming byte. Furthermore, wakeup
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
41 from deep sleep takes a non-trivial length of time, thus if someone tries to
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
42 send lots of data to a Calypso UART while in deep sleep, quite a bit more than
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
43 just the first character will be lost: I did some experiments to characterize
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
44 the delay which needs to be inserted between the first "sacrificial" wakeup
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
45 character and the subsequent character which is expected to be received
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
46 correctly, and 40 ms wasn't enough, whereas 60 ms did the trick.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
47
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
48 So how can one have reliable communication with a Calypso GSM device over a
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
49 UART if the GSM device goes into and out of deep sleep at times which are
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
50 unpredictable to the external host and if sending characters to the Calypso
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
51 during deep sleep causes those characters to be lost? The solution involves a
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
52 special protocol:
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
53
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
54 1) On the Calypso side, TI's reference firmware implements a UART activity
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
55 timer: every time some characters are received at a UART, the timer is reset to
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
56 10 s, and until that timer expires, the GSM device is not allowed to go into
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
57 deep sleep.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
58
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
59 2) Host systems sending command traffic to Calypso modems need to keep track of
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
60 how much time has elapsed since the last time they sent something to the modem,
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
61 and if enough time has elapsed that the modem is now allowed to enter deep
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
62 sleep, the host needs to perform a precautionary wakeup transmission before the
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
63 actual desired one.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
64
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
65 What is a precautionary wakeup transmission? The idea is to send something to
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
66 the modem can be either accepted or lost by the latter: if the modem happens to
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
67 be awake at the time, the transmission will be received normally, and if the
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
68 modem is in deep sleep, the transmission will be lost but will cause the modem
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
69 to wake up and start the 10 s UART activity timer. Our FC host tools currently
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
70 use the following wakeup transmissions:
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
71
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
72 * On the AT command channel we send A-delay-T-delay-CR, i.e., AT and a carriage
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
73 return (3 characters total) with delays inserted in between; each of the two
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
74 delays is currently set to 30 ms based on empirical testing. We expect the
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
75 response to be either AT<newline>OK<newline> (echo of command followed by OK
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
76 response) if the modem was awake or just <newline>OK<newline> if we woke it up:
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
77 if we are waking the modem from deep sleep, our initial characters will trigger
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
78 the wakeup sequence but will themselves be lost, and the modem is expected to
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
79 be awake with UARTs working by the time the CR comes in; we make use of a quirk
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
80 of TI's AT command interpreter implementation in that sending a CR by itself
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
81 produces a <newline>OK<newline> response.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
82
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
83 * On the RVTMUX interface we send a string of 64 zero bytes followed by 100 ms
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
84 of delay; it is certainly overkill, but this approach was implemented back in
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
85 2013 (near the very beginning of FreeCalypso) and has worked without any
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
86 problems ever since, hence we are not changing it.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
87
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
88 In the case of RVTMUX, our serial communication engine through which everything
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
89 funnels is rvinterf. Rvinterf will do the "wakeup shot" the first time it sends
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
90 anything to the target, and for all subsequent transmissions it will consider
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
91 the time since the last transmission: if it is greater than a set threshold
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
92 (7 s by default), the wakeup shot is sent again. Thus there will be no
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
93 extraneous wakeup shots and associated delays during reasonably continuous
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
94 back to back communication, but the wakeup shot delay will be incurred if
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
95 rvinterf is killed and restarted or if a non-trivial pause occurs in the
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
96 communication flow.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
97
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
98 In the case of AT commands, our fcup-* tools described in the User-phone-tools
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
99 article go through a back-end program called fcup-atinterf which does the serial
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
100 talking, and the latter helper program is responsible for the wakeup logic.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
101 However, fcup-atinterf is not a daemon like rvinterf, it is run anew for every
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
102 fcup-* user command, hence every fcup-* command currently involves the wakeup
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
103 delay step. It is certainly inefficient, but the underlying philosophy values
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
104 reliability over efficiency.
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
105
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
106 The one remaining use case which has not been addressed at all yet is the GSM
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
107 07.10 MUX; the current plan is to investigate it after the fc-host-tools-r9
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
108 release and after we get FCDEV3B V2 boards which will hopefully be free from
19cabe7c8e08 doc/Deep-sleep-support article written
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
109 the sleep mode bug that afflicts FCDEV3B V1.