Motorboating == USB overcurrent -> emergency shutdown -> NoPower -> autostart

[Andy Green]

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Somebody in the thread at some point said:
| Andy Green wrote:
|> I just saw my backup battery is at 0.4V.
|
| Mine's at 1.52V and I've seen it retain PMU settings, so the phenomenon
| does not depend on entering NoPower.
|
| BTW, the trace isn't very symmetrical on my system. Recovery is about
| twice as fast as the plunge into doom. (Also your screenshots show
| this.)

I guess it's true, it depends on the load resistance to discharge and
the current-limited regulator source impedence to charge, they're not
really related.

|> It can work out if during startup Vsys is going under Vth(sysmin) which
|> is hardcoded at 2.5V, it forces an "emergency shutdown" and pushes us
|> into SAVE -- that is what gets us the sticky power loss.  Then it goes
|> under Vth(syspres) 2V limit and we "reset and enter the NoPower state".
|
| Also dropping all the way down to 2V seems to be optional. I have
| the end of the drop hover around 2.44V at the moment. (After shorting
| the backup battery.)

Still, emergency shutdown --> Save will get us the right behaviour for
the first half either way.  It's quite possible SAVE -> STANDBY makes
pcf50633 "see" USB power present as "USBINS" and makes it go active
again even with a good battery.

- -Andy
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