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

Rask Ingemann Lambertsen ccc94453 at vip.cybercity.dk
Thu Sep 24 21:28:13 CEST 2009

On Thu, Sep 24, 2009 at 10:46:44AM -0300, Werner Almesberger wrote:

> One question: what do we do with the evil backup battery ? I've written
> ECN0040 to discuss the issue

   OK, I thought we weren't going to try doing something about it, but here
goes (in the order of the ECN):

   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. But at least in my GTA02, the backup
battery doesn't last for more than 5-10 minutes anyway, so maybe we don't
have to do better than that. The interesting use cases for a backup battery
or similar storage device are:

1) Keep time while swapping SIM and/or SD card. A few minutes at 50 uA.
2) Keep memory in suspend while swapping battery. 10-20 seconds at 8 mA.

   The latter would require that we figure out something with the adapter
input of the PCF50633 and some means of recharging the supercapacitor or
whatever we come up with.

   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.

Rask Ingemann Lambertsen
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