[gta02-core] PMU cleanup

[Werner Almesberger]

I wrote:
> Now, with the GE865, the whole arrangement may have to change, but we
> have to find out about the current requirements on each rail. The
> GE865 has separate power inputs for the baseband processor and the RF
> amplifier, just like our Calypso circuit does, so it may be possible
> to use the same concept.

I'm writing down that question for Telit, and the more I write, the
less I like that part.

The idea of cutting power to the side that has the oscillators while
leaving the side that actually puts things on the air has its merits,
but it also has great potential for unintended consequences, such as
the RF amplifier picking up EMI and sending that, or a sneak current
crawling back into the baseband and making it do *something*.

The GE865 has a feedback mechanism that tells us if it's powered up
or down (PWRMON), so we should have considerably better control over
the modem's state than with the Calypso, even without such a switch.

- Werner