u-boot fix to charge empty battery

Andy Green andy at openmoko.com
Thu Oct 9 17:45:47 CEST 2008

Hash: SHA1

Cédric Berger wrote:
> When my battery is empty, I generally cannot even turn on the phone
> into NAND U-boot menu (power+aux), even with charger plugged in.

Yes that's what I see here too with an A5 board.

> But  I can go to NOR U-boot menu (aux+power). (sometimes only after a
> while being plugged and several tries...)

Seen it too.

> Is it just due to incorrect behaviour of current U-boot (well last I
> tried is about 15 days old), or also because loading U-boot from NAND
> needs more power ?

I think it is the changes to U-Boot the last few months, and the
different VB_SYS capacitor on A5 that make the different behaviours.  On
an A6, things are more civilized.

There is nothing special about NOR boot path for power, NAND should be
work effectively the same, so I guess it is changes to the code.

> When I manage to get to NAND U-boot it generally dies not long
> after... but there the 8sec. shutdown might have happened too (?) And
> booting indeed looks like sucking too much power.
> So I have to go to NOR U-boot, boot once and shtudown (time to do that
> is enough to charge battery so that I can go back and normally boot)

Yes I know what you mean :-/

> (Last time by chance my batt finally charged enough -waiting hours-
> without booting -not always the case-...
>  because my NAND rootfs was "dead" so I could not boot via NOR U-boot)

The possibility of such difficult behaviour is introduced really by PMU
powering from NOPOWER with charger forced off.  If CPU does not come up
enough to enable it then charging isn't even happening.

- -Andy
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