[Arm-netbook] [EOMA68] RS232 on SoCs

[joem]

On Mon, 2013-09-16 at 17:37 +0200, Henrik Nordström wrote:
> sön 2013-09-08 klockan 11:31 +0100 skrev luke.leighton:
> 
> >  when the AXP209 Power Management Integrated Circuit is fed 3.3V into
> > its pins whilst it is powered off, it can get damaged.
> 
> It doesn't get damaged, but gets into unexpected state requiring a power
> cycle to return to normal operation.

I can verify something like that is happening.
Haven't found the exact cause in hardware yet.
The symptoms seem to be spinning itself around the mmc card.
 
The mmc card is being kept powered up which is
getting its power from RS232 3 pins only!!!
So it requires the mmc card to be ejected, or a very long
time until controller inside mmc card decides it needs to reset.

The simplest suggestion I can make is to put 330R between the +3.3V
rail and gnd of the mmc. But I have not tried it yet to
know whether it can work.