[Arm-netbook] EOMA-68 passthrough implementation

[lkcl luke]

On Tue, Jul 10, 2012 at 2:05 AM, Derek LaHousse <dlahouss at mtu.edu> wrote:
>
>> I'll follow up with phil when I'm ready to begin and after I've
>> familiarized myself with your git repo. Thank you for the info.
>>
>> >  would anybody like to help finding the required mid-mount HDMI and
>> > USB-OTG sockets?  ryan, are you considering doing an audio IC of some
>> > description on the pass-through card, or just leaving that for now?
>> > (can always do a revision 2.0).
>>
>> I was planning just to use standard connectors for the signals that
>> are clearly ethernet, or SATA, etc. For all the GPIO/I2C pins I'd
>> probably use 0.100"-center plated holes and let the user solder
>> something.
>>
>> If there were an IC that could pull the audio out of the HDMI signal
>> and put it on a headphone jack, I might be interested in using it.
>> However, I don't plan on getting too fancy, and if it bloats the cost
>> much, I would hesitate.
>>
>
> I'm a little confused by the audio direction.

 digital signal generation is the *opposite* direction from CPU Cards.
 however in the case of audio you would still have a mic and
headphones, one is input, the other is output - you can't reverse
those :)

>  A pass-through card
> should be receiving video signals on the "external" side of the EOMA
> card, and providing data to the PCMCIA side.  To pass the audio, it
> would need to break the signal out of the HDMI and then drive a USB
> sound card, right?

 a typical HDMI IC used in LCD monitors does this kind of conversion
anyway (just not to USB).  typically it's to AC97 or I2S audio.
however the up-front licensing costs on those stupid HDMI ICs, as
someone else learned and reported on this list, is around $50,000.  so
fuck that.

 the alternative is just to ignore HDMI audio and lay down a USB audio
IC.  however you can just as well go get a USB audio stick off of ebay
and it would achieve the same effective result.

 bottom line: don't complicate things by having audio - at all.

> It's also important to pass the I2C through to the front of the EOMA
> passthrough.  A system emulating the EOMA would need to be able to read
> the EEPROM on the motherboard, as part of the spec.

 achh, i'd forgotten about that.  hmmm, in a commercial pass-through
card that might involve dropping an 8-bit micro onto the PCB.  darn.

 l.