u-boot low-battery handling

[Mike Montour]

Mike Montour wrote:

> I'll try to send an updated u-boot patch in the next day or two.

I've attached a patch with my most recent changes, and there is a 
corresponding GTA02v5 binary at 
http://members.shaw.ca/mmontour/neo/u-boot-mm-2008083001.udfu for anyone 
who wants to try it out (at his/her own risk). There might be problems 
on pre-production GTA02v5s that don't have the LED-current-limiting rework.

This version flashes the Aux LED once at startup and then checks the 
battery level. If the battery is very low it gives three quick flashes 
on the Aux LED and then shuts off. If the battery level is above this 
threshold but still below 3.4V it loops for about 10s waiting to detect 
 >= 500mA USB power, flashing the Aux LED at a slower rate. Pressing the 
Aux button will bypass these checks.

When the device is turned off cleanly (through the neo1973_poweroff() 
function), the PMU is programmed not to wake on USB and to limit the 
battery fast-charge current to 100mA. This probably violates the USB 
battery charging specification, but it is necessary (at least on my 
hardware revision) to recover from the case of a fully-discharged 
battery whose internal cutoff has triggered.

This patch is still a work in progress (probably not suitable for 
merging into the stable tree), but I'm going to take a break from it for 
a while and look more at Qi and the Linux PCF50633 driver.
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