[olpc-nz] Battery LED flashing

[Tabitha Roder]

We plugged in an XO-1.0 with an unknown state LiFePO4 battery (may have been
fully discharged a week before, or may have been shut down properly) and the
battery LED flashed instead of coming on solid like charging normally does.
The battery information in /sys indicated low battery voltage (5.something)
but otherwise good health and charging state. We tried the battery in a
different XO-1.0 and the same behaviour resulted. We left it plugged in
overnight and it appears to have charged normally and the battery now runs
the laptop (when it was doing the flashing charge, the laptop would switch
off immediately when you unplug the charger).

http://wiki.laptop.org/go/Power_management#Battery_LED indicates flashing on
charge means trickle charging. Sadly we didn't find this page when it was
happening so cannot fully confirm it was flashing orange and with the 4
blinks, pause pattern. This page also doesn't give any clues as to why a
battery might be trickle charging.

http://wiki.laptop.org/go/Hardware_specification#Battery suggests that the
battery has a Maxim DS2756
<http://wiki.laptop.org/images/e/e9/DS2756.pdf>chip in it, but this
chip only monitors one cell, so I guess there are two
such chips? The /sys interface only gives information about the whole
battery, it doesn't tell you about the state of each cell. The specification
pdf on the Hardware_specification page describes the Embedded Controller
interface to the operating system in terms of "Battery", not "Cell" so I
guess it doesn't expose each cell either?

Is it possible to see each cell's voltage separately from within the
operating system or the open firmware? I guess if there is no other way, it
wouldn't be terribly hard to program a microcontroller to talk to the cell
monitors over the 1 wire bus.


Kind regards
Tabitha Roder
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