Sansa Battery Measurements

This is about getting the battery level handling of the Sansa straight. Issues are tracked in FS:6860 Help needed Please provide battery_bench data to improve accuracy of the discharge curve.

Patching battery bench

battery_bench has to be patched to work with sansa. A Flyspray bug report has been filed here: FS#8070 - Sansa battery_bench plugin buffer overflow

The quick and dirty fix provided here is that no measurement buffering is being used but instead an instant file update is forced when voltage values are changing. A source code patch containing this fix is also available in the Flyspray entry FS#8070.

change line 232, add got_info

    do
    {
        if(!in_usb_mode && got_info && 
            (exit || timeflag || got_info || rb->ata_disk_is_active()) )

Limits - to be confirmed

Fully charged:
- 4,20V ?
Low power shutdown (done by bootloader?):
- 3,3V ?

Charging

Battery charging is controlled by the integrated charger of the PP5024 SoC, which allows configureable charging current and voltage. The charge control register is currently not configured, resulting in a default maximum charging current of 50 mA and maximum charging voltage of 3.9V. This makes charging slow (and probably incomplete) compared to the original firmware. Furthermore, while USB is not supported yet by rockbox on the Sansa e200, the USB interface is allowed to draw only 100 mA instead of the possible maximum 500 mA.

In the mean time:

Use the Sansa original firmware for charging instead.
Charging with a dedicated charger with rockbox will not work at full speed.

Discharging

battery run 03-Apr-2007, Rockbox revision: 13002

plot:
battery_bench.txt: 2007-04-03

battery run 31-Aug-2007, Rockbox revision: 14552

battery_bench.txt: 90mb .ogg vorbis q8; runtime: 15:53:52

battery run 01-Nov-2007, Rockbox revision: r15294-071025

battery_bench.txt: default settings, mix of Q6 vorbis (70-80%) and miscellaneous MP3
I did not patch the battery_bench plugin, so only the final five hours are in the file