current focus / Removing PMU problem in future

Andy Green andy at
Fri Jul 11 13:53:33 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| Andy Green wrote:
|> This is yet another case for an always-on MPU to solve it in future
| This one is actually a little bit trickier: even if we had that
| MPU, it could do nothing to change what the PMU is doing, since the
| PMU doesn't even get out of reset. From section 8.17.11 of the PMU
| manual:
| | The I2C-bus module is only enabled in the Active state when the
| | reset for the host controller is released

You are right, but it doesn't stop us.

We need to add a P-Channel MOSFET on at least AUTO controlled by MPU to
be able to remove the rail from its load.

~ - MPU disconnects high power loads
~ - MPU brings up PMU fully
~ - MPU waits for nRSTHC from PMU is high, writes low "always active"
~   current limits to PMU by I2C
~ - connect loads in turn according to power sequencing demands
~ - MPU polls until all power rails to be OK
~ - MPU brings CPU out of reset using MPU GPIO

- -Andy
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