[gta02-core] ECN0040: Remove backup battery (Was: ecn progress)

Werner Almesberger werner at openmoko.org
Fri Sep 25 00:10:42 CEST 2009

Rask Ingemann Lambertsen wrote:
>    When the backup battery was last discussed, I looked for
> (super)capacitors as a replacement, but didn't find anything with near the
> same capacity in a similar space.

Once upon a time, I think it was for one of the GTA03 designs, we looked
for one and found something with the same size and some huge capacity.
But someone was afraid the PMU might not like a capacitor.

> But at least in my GTA02, the backup
> battery doesn't last for more than 5-10 minutes anyway,

That's bad :-( I guess it just underlines that the backup battery isn't
a long-lived component.

> 1) Keep time while swapping SIM and/or SD card. A few minutes at 50 uA.

Hmm, if we can keep this in the <= 2 min range, the "keep time in the
modem" approach would be feasible (220 uF). Better with <= 1 min (100

> 2) Keep memory in suspend while swapping battery. 10-20 seconds at 8 mA.

Hmm, for future study.

>    I don't think we've had problems with undefined state on power up. If we
> manage to power up at all, we can (and do) load our own settings anyway.

Yes, I think we dodged this bullet so far. It's more an analysis
problem: for each power-up problem that pops up, you have to include
the possibility that the PMU _may_ have been in an odd state. Things
would be much simpler if one could exclude that possibility.

- Werner

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