Artix 7 1080p HDMI / timing constraints


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I have a number of FPGA boards, including several Papilios, and recently acquired a Digilent Artix 7 CMOD A7. The nice thing about this board is the form factor (can plug into a breadboard), and the inclusion of a large SRAM (not SDRAM!).

I found a number of projects on Hamsters web pages (excellent learning material BTW), specifically a project to use this board to output 1080p over a HDMI cable.

I have spent the past few evenings converting the VHDL code into Verilog. It's not that difficult. I think that I have spotted a bug where the constant 720 is used instead of 1080 (the video is 1080p, but perhaps the code was original for 720p?). I have brought hsync and vsync out to pins in order to check timings on a scope (that's how I found the bug). I was puzzled as to why I was seeing no signals whatsoever on the high-speed TDMS differential pins, until I finally realised that they need 50ohm pull-ups to +3.3V. This is normally done at the other end of the HDMI cable, but I don't have one currently connected. I popped in some resistors and finally saw some waveforms on the differential pins. They were pretty nasty. I really need a scope with much higher bw!

Just today I got a HDMI breakout board, ordered from Ebay. I will now be able to connect a HDMI cable to a monitor.

To get started I really want to drop down the timings from 1080p to 576p (UK 50Hz standard definition), but I can't find the pixel numbers for the vsync, front/back porch etc. If anyone has a definitive list, please let me know! I can compile for either 1080p or 640x480 VGA timings (no idea if this will be recognised over HDMI).

At 1080p I am failing timing analysis. This is where I struggle. I am using a PLL to boost the 12MHz xtal to the 100MHz needed by the original code. I am trying to define in the XDC the clocks. I know how to define the XTAL clock, but I am having problems telling Vivado about the internal clocks. In fact I am not sure whether I really need to or whether it can  infer the clocks from the MCM parameters? I tried using the timinng constraints wizard, but it wanted to add constraints for the TMDS outputs, but I had no idea what numbers to use.

Any guidance from anyone who has played with HDMI would be greatly appreciated.

Once I have something (low res) working with the CMOD-A7 I will go back to the Papilio Pro and get something working here.

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