GTA02 Power Glitch Reason Found

[Andy Green]

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Somebody in the thread at some point said:
> Andy Green wrote:
>> VB_SYS has no decoupling at all on our design.
> 
> Nice catch !

Thanks!

>> This is a real problem that is going to require manual rework before
>> ship, but that should be possible neatly from the VB_SYS end of the
>> recently added 10K resistors for EXTON[1..3] to 0V on C1764.
> 
> We're very lucky :-) What sucks is that VB_SYS isn't easily accessible
> in any of the older designs, so reworking any pre-v5 hardware will be
> fun ...

Well soon there will be plenty of A5s so the old GTA02 will be
deprecated.  But it is a whole new ballgame debugging these kinds of
boards where many chips have underside interconnect and there isn't any
outer layer tracking to speak of.  And laser vias :-O

It was a problem since GTA02 A1 where we changed to the PCF50633... it
can explain a long list of unstable PMU behaviour -- including the
"turning on the GSM unit kills a lot of phones" thing, "some phones
won't play with USB-only" and so on.  The rework is probably going to
make a headache but this is great news if we killed a bunch of pretty
scary monsters all at once.

- -Andy
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