# HG changeset patch # User Mychaela Falconia # Date 1650002376 0 # Node ID 91352355857cbe750ba0ba770c3e52629adc83a1 # Parent 78d4d362c08688f2dbc987fb9c4716af106e2edf FC-handset-spec: document beyond-USB rescue provisions on FC Venus diff -r 78d4d362c086 -r 91352355857c FC-handset-spec --- a/FC-handset-spec Fri Apr 15 04:55:26 2022 +0000 +++ b/FC-handset-spec Fri Apr 15 05:59:36 2022 +0000 @@ -1507,7 +1507,7 @@ Our Venus development board will include the same USB subsystem as intended for the final FC Libre Dumbphone handset, as described in sections 1.11 and 1.12, consisting of a USB mini-B interface connector, a charging on/off switch with -the charging circuit behind it, and the FT2232x subsystem of section 1.12. +the charging circuit behind it, and the FT2232D subsystem of section 1.12. This design is a radical departure from our previous development boards which bring out the two Calypso UARTs in their raw LVCMOS form, leaving the USB @@ -1559,7 +1559,7 @@ 3.3.2.1. Linux kernel patch requirement -The FT2232x USB subsystem implemented on FC Venus will include the boot control +The FT2232D USB subsystem implemented on FC Venus will include the boot control feature originating from DUART28C, as described in section 1.12.3. This hardware feature has an implication for developer-users of this board: anyone wishing to play with a Venus board beyond already-flashed fw (i.e., anyone @@ -1586,15 +1586,22 @@ 3.3.2.2. Board bring-up order -With the FT2232x USB subsystem integrated on the Venus board, this subsystem -will become the only way to access Calypso UARTs for initial bring-up of a -freshly populated board. Furthermore, our DUART28C-based boot control mechanism -will be the only way to trigger RPWON and nTESTRESET boot controls - there will -also be a PWON button (see section 3.6), but that one is intended for higher- -level end user functions after FC handset fw has been loaded and after all other -bring-up tasks are completed on each board. As a result of these factors, our -FT2232x USB subsystem becomes part of the critical path for board bring-up, and -it will in fact become the very first part to be brought up, before Calypso. +The on-board FT2232D subsystem will be the preferred way to interface to the +two Calypso UARTs on FC Venus, and also the preferred way of driving RPWON and +nTESTRESET boot controls - if everything goes according to plan. However, to +guard against inoperable boards in the unfortunate event that the built-in USB +subsystem doesn't work as designed, there will also be a "rescue" 10-pin DUART +header on the board. If all USB subsystem components are populated on the +board as we currently intend, the "rescue" DUART header MUST NOT have anything +connected to it, other than oscilloscope probes - however, if a need arises to +operate a Venus board via an external DUART28 or other adapter, then some +components will need to be removed from the USB section of the board to prevent +the scenario of two fighting drivers. + +There will also be a 3-pin boot control header, bringing out RPWON and +nTESTRESET, but this provision does not present the same stringent single driver +requirements as the "rescue" DUART header, as all drivers for these boot control +signals are open drain. The charging switch will need to be off during board bring-up, and it is expected to remain off during most development activities on FC Venus, to be @@ -1696,14 +1703,20 @@ fw architecture - instead its control will be absorbed into our R2D BLRR control mechanism on the final handset where this backlight will be added. -3.6.1. No boot control buttons +3.6.1. Limited boot control buttons The Mother's original idea for FC Venus was to implement pushbutton switches for all 3 boot controls as in PWON, RPWON and nTESTRESET. However, now that we are -integrating the FT2232x USB subsystem of section 1.12 and the boot control +integrating the FT2232D USB subsystem of section 1.12 and the boot control mechanism of section 1.12.3 as a non-removable part of the Venus board itself, -pushbutton switches for RPWON and RESET are being eliminated, leaving only PWON -in the "END" position in the main keypad. +the pushbutton switch for RPWON is being eliminated, leaving only PWON in the +"END" position in the main keypad and a rare-use RESET button. For additional +context, when I first decided to integrate the FT2232D subsystem with boot +control, I was going to drop the RESET button as well - but then I decided that +it would be more proper to include at least a footprint for one. My current +intent is to populate an actual button for RESET, but to use a different switch +part with a shorter actuator and a greater operating force, reducing the +probability of accidental resets. 3.7. Audio interfaces