FCDEV3B sleep mode bug update

Mychaela Falconia mychaela.falconia at gmail.com
Tue Jan 23 04:48:05 UTC 2018

Hello FreeCalypso community,

I finally got a breakthrough in the wild goose chase after the sleep
mode hardware bug on our FCDEV3B boards: the self-reboot behaviour on
the AT+CFUN=1 command with all sleep modes enabled went away when I
replaced the high-capacity flash+RAM chip on one experimental board
with the smaller-capacity K5A3281 that was used by Openmoko.  Thus we
now know that the difference between Openmoko's working original and
our derivative thereof that's causing the sleep mode bug is the memory
IC change.

My next goal is to figure out how to fix the erratic behaviour without
reducing the memory capacity, i.e., how to make sleep modes work
correctly without giving up the high-capacity Spansion flash+pSRAM
chip we are currently using.  The inspiration to use this particular
chip (Spansion S71PL129NC0HFW4B) came from the Pirelli DP-L10, and the
part number was obtained by reading the marking on the flash+RAM chip
inside a disassembled Pirelli DP-L10 phone.  These chips clearly work
fine in these phones, and all sleep modes work fine when we run our
own fw on the Pirelli target, thus it is clearly possible to use this
memory chip in a Calypso phone or modem.

My next experiment will be to try increasing the bypass capacitor
values on the V-FLASH and V-SRAM power supply nets from the Iota ABB
to the memory chip - stay tuned.

Hasta la Victoria, Siempre,
Mychaela aka The Mother

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