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

[Werner Almesberger]

Andy Green wrote:
> I think there is a bit of confusion here.  "Standby" is a separate issue
> that does not need battery backup on MSP430.  IO_3V3 rail is up during
> standby.  MSP430 will be up during standby.

Not quite :-) PMU.Standby != Linux.suspend

When we suspend, the CPU remains in PMU.Active, and all we do is switch
off some of the regulators we don't need. This is your scenario where
IO_3V3 is active.

However, PMU.Standby really means "no power to the system". (You can
change that to some extent by setting bits in STBYCTL1 and STBYCTL2,
but we don't do that.)

Here's the matrix of states as I understand things:

PMU	CPU	Linux
-------	-------	------------
NoPower	off	off
Save	off	off
Standby	off	off
Active	SLEEP	suspend
Active	IDLE	on, CPU idle
Active	NORMAL	on, CPU busy

CPU.off means completely unpowered. In CPU.SLEEP, I/O and VDDalive are
powered, core and PLLs aren't, (I'm too lazy to look up whether VDDmop
is powered as well ;-) I guess it is.) CPU.NORMAL has all rails powered.

- Werner