[Arm-netbook] [EOMA68] RS232 on SoCs

[joem]

On Mon, 2013-09-16 at 21:43 +0200, Henrik Nordström wrote:
> mån 2013-09-16 klockan 15:47 +0000 skrev joem:
> 
> > 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.
> 
> It's not only SD card. Actually I haven't had much issues with SD cards
> related to this, only AXP, resulting in the AXP powerig up but not
> responding to i2c requests.
> 
> > 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.
> 
> Maybe. Guess it depends on the resistance in the UART dongle and also
> UART0 RX -> VCC3_3 internal resistance at power off. But will cost a bit
> of additional power drain during normal usage.

The power drain is 10mA - about same as having an extra LED on.
It should be enough to kill any voltages that are outstanding
if its being fed from 3 pins of RS232 interface.

I'll get a chance to try out a few hardware checks this evening and
hopefully get more clues.