u-boot low-battery handling
mail at mmontour.net
Thu Aug 28 19:11:37 CEST 2008
Joerg Reisenweber wrote:
> I strongly recommend reading of
> Battery Charging
> First approach like above seems the right way to go. Though device should
> *try* to boot up anyway and simply die when current-limiter on USB-inbound
> current cuts out and we got no battery backup.
That's what breaks the GTA02v5 when the battery cutoff has activated -
the PMU tries to go into Active state, but this triggers a brownout on
Vsys when it activates some of the LDOs (based on how Andy explained it
on the hardware ML), before the CPU can do anything. Not waking on
insertion allows the charger to bring the battery out of the cutoff
state, which takes ~10s.
If this problem does not exist on newer models then this behaviour of
disabling wake-on-USB could be applied only to the older hardware
revisions (although it would be more confusing to users if older and
newer units behaved differently on charger insertion).
I suppose we can live with the need for a "jump-start" battery once the
rest of the power-management code matures to a point where the battery
will never become discharged far enough to trigger the cutoff.
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