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

Andy Green andy at
Thu Apr 24 14:00:02 CEST 2008

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Somebody in the thread at some point said:
| Am Do  24. April 2008 schrieb Andy Green:
|> Somebody in the thread at some point said:
|>    I don't think we
|> need this since we only want RTC to stay up and the RTC can be in PMU.
|> If it is true we need to keep RTC in PCF50633 and keep the battery on
|> there only.
| RTC on MPU is much better, for you might want realtime events/tasks to
| triggered/done by MPU. It's an annoyance to have the RTC in PMU just
| there happen to be a RTC there and incidentally also a backup battery.
| FOR do we need a RTC on PMU?? It would be even less weird to use the
one of
| 6400 and stay close to IndustryStandardArchitecture(ISA=PC=IBM)...

Only because it is the (allegedly) working setup on GTA02 we can cut and
paste at low risk of it acting different to GTA02 (for better or worse).

If we use one of the other choices, 6400 or MSP430, they need to share
the battery because only the PMU charges it, and we want the PMU to have
the battery so the is no variation in behaviours there against GTA02.

I went to look up all the RTC standby power data but found none :-)
6400 and MSP430 are silent about it.  PMU says 60uA in "save" state with
32kHz running.  IIRC we use PMU 32kHz osc as the definitive 32kHz for
the board anyway.  So much else to worry about I like it if we take a
conservative choice and worry about the next thing.

- -Andy
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