[Arm-netbook] EOMA-68 passthrough implementation

[Ryan Mullen]

On Wed, Jul 11, 2012 at 2:47 PM, lkcl luke <luke.leighton at gmail.com> wrote:
>  anyway: all of this is moot as far as a "simple" passthrough card is concerned.

Good enough for me!

Based on a quick skim of the datasheet from the TI HDMI->RGB converter
IC, there appear to be no control pins that are expected to be tied to
an MCU. Therefore, I don't see the need for adding extra smarts in
that regard, since negotiation of all the extra "stuff" should happen
in front of and behind the passthrough card.

We expect the I2C EEPROM to be onboard the EOMA68-compliant
{tablet,LCD,keyboard} to be read by the standard PC-class device that
connects to the USB/Ethernet/HDMI connectors. The question, then,
becomes: what connector would we use for the I2C lines that are passed
through, so that they may be easily managed? If we wanted to add a
USB->I2C IC, (for example, FTDI FT232H), we could just slap on a
mini/micro USB socket and the FTDI device should be able to act as a
I2C master. We could then speak to the I2C bus with a ttyUSB or
hyperterminal, or more native interaction if someone wants to write a
program to do it. It's not the cheapest IC around, so maybe some
shopping would be in order, but it's an example of one way to go.

Another option is to leave it up to the user to sort out and just make
two I2C pins available. Users could use a Bus Pirate or Aardvark or
something to talk to it.

What about this mechanical non-interoperability fascia plate business?
Is there anyone out there who handles mechanicals? Where should the
screw holes in the passthrough card's PCB go? I suppose the placement
and dimension of the holes should be standardized because AFAIK the
intent is to use the same fascia plate for all EOMA-compliant modules.
Alternatively, is the fascia plate attached to the PCMCIA housing
itself, without interfering with the PCB within?

Thanks, all, for the discussion.
Ryan