HDMI transceiver wiring

[tnt]

Please tell me you didn't wire the transceiver like it's wired on the zedboard ....

They seem to have chosen the only way to wire it that doesn't support any RGB mode and only support YCbCr AFAICT.


Cheers,

Sylvain

[theover]

That sounds like similar spoiling of the electrical circuit as in previous Xilinx boards (like the well known Spartan 3e starter board), where all kinds of signals of ram/rom and other (on itself nice) chips are such you just can't make a fancy computer out of it without getting you display and other needed IO in a twist...

[bswiec]

YCC-only is not an arbitrary choice... 422 (or 420) YCC takes less pins on the board/fpga.

Those boards aren't designed to be an end-product computer for hobbyists. They're to sell FPGAs. If Xilinx can squeeze an extra peripheral or two on the board that will appeal to other customers by using 422 YCC for video, it would make good business sense to do so.

Just wanted to point that out for fairness-sake.

[theover]

Baaahhhaaahhaaa, man those chips have hundreds of pins, and user connectors too, so: BS.

[bswiec]

By the way, the color space converter cores from xilinx are free and don't take up too much space. So taking your RGB source to 422 YCC wouldn't be that hard.

[bswiec]

Many of the pins are MIO. It's not like that's the only thing on the board. I don't see too many spare pins in the schematic...

FMC support (user I/O) is important. It allows you to go buy your RGB HDMI transmitter if you want...

I'm not necessarily saying it is the best choice. Just that it isn't arbitrary.

[tnt]

If you wire the D[35:24] you can do YCbCr and RGB at 8 bit per component. And if you want 10 bits, go to D[35:21] that's still only 15 bits (i.e. one line less than what they did on the zedboard).

And in any case, I don't really care why they did it that way on the zedboard, I want to make sure they didn't make it that way on the parallella.

[theover]

There are FPGAs with varying pin counts, I agree to want the best option for the Parallella, and I'd rather have the option for $99 and say $150 or whatever to get all the nicer options on board. It's just that I know for sure other boards suffer from spoiling choices: who's responsible for those choices, and what their designers "profile" is, is an entirely different matter, or course.

Even current consumption couldbe part of the considerations: a long HDMI cable with 1080(P) signals on it may require more drive power than the whole board uses for the rest..

[bswiec]

Yeah, that's a fair point. I'm not really a board-level guy, so I could easily be missing something!

I'm not terribly familiar yet with the parallella platform (since I haven't gotten one yet ha!), but taking a second look, it appears that the HDMI transmitter is built in the FPGA fabric and is not an external chip, yeah?

[aolofsson]

Sylvain,
Could you explain why this is so important? Not sure I understand the issue. At this point we likely do have the same limitation as the zedboard. If this is turns out to be a major flaw, we will definitely change the final design.
Thanks,
Andreas