next-generation (now) MPU discussion / Backup battery on PMU only

Werner Almesberger werner at openmoko.org
Fri Apr 25 10:02:55 CEST 2008


Andy Green wrote:
> Then a wise person would disambiguate it when they talk about it,
> because "standby" is normally what we use to talk about global device
> standby.

Great minds think alike ;-) That's why I wrote "PMU.Standby":

| Allow us to get out of PMU.Standby, maintain GPIOs while in PMU.Standby,
| etc.

> There was plenty written there about the PMU.  But the issue was about
> who gets to drink our precious backup battery.

Well it started with "how do we power the MPU", and that's still the
question. The backup battery only came up as a way to do it.

> ''The ONLY scenario we consider is no external power, and battery is
> removed.  Why do we need MSP430 state to survive it?   I don't think we
> need this since we only want RTC to stay up and the RTC can be in PMU.''

Well, this statement isn't true in the way we currently use the PMU.
If the PMU is in its Standby state, all its regulators are down, thus
the MPU needs some other power source - be it a direct link to Vsys or
the backup battery.

>From earlier in this thread:

| Andy Green wrote:
| > Well fine, but what does giving the MSP430 the battery backup actually
| > get us?
| 
| Allow us to get out of PMU.Standby, maintain GPIOs while in PMU.Standby,
| etc.

- Werner




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