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Original question:

SN65DP159: SN65DP159RGZR

SN65DP159: HDMI 2.0 no output, screen flickers black

Andrada Zoltan
Prodigy 10 points
Part Number: SN65DP159


We are having issues with HDMI 2.0 data rates on a custom PCB that uses this component. Any screen resolution / frame rate combinations that result in a data rate < 3.4Gbps are working just fine. However, whenever we go into data rates > 3.4Gbps I am getting no output from the HDMI. The screen flickers black for a moment, then the embedded software on the board reports the HDMI TX stream has gone down. The stream comes back up shortly after and the process loops endlessly.

I have tried the same monitor / cable on a development board containing the same FPGA SoC, and HDMI 2.0 rates are working just fine on there. So the issue definitely lies with the new custom board.

Here are the register dumps from the working case on this board (< 3.4Gbps) and the non-working case (> 3.4Gbps):

    

Can you provide guidance for further investigation into this issue?

Thanks.

  • 0
    TI__Genius 13310 points

    Hello, Andrada,

    Could I take a look at your schematic?

    Do you have any eye diagrams of the output that I could take a look at as well?

    Are you seeing this issue with just one sink or have you tried multiple sinks?

    Thanks,

    Zach

  • 0 in reply to Zach Dryer
    Prodigy 10 points

    Hi Zach,

    Can I share the schematic with you privately?

    We do not have any eye diagrams as we don't currently have a TI USB-I2C converter that we could use with the EyeScan tool.

    This issue is present on all sinks that we have tried with our custom hardware. These same sinks work just fine with the Xilinx dev board.

    Thanks,

    Andrada

  • 0 in reply to Andrada Zoltan
    TI__Genius 13310 points

    Hello, Andrada,

    Yes you can share the schematic in a private message or contact your local FAE to send it to me.

    Do you have an oscope that you can use to get a eye diagram? 

    Thanks,

    Zach

  • 0 in reply to Zach Dryer
    TI__Genius 13310 points

    Hello, Andrada,

    1. You mentioned in our chat that you set the DP159 DEV_FUNC_MODE to 0x00 (Redriver mode) and could see video out to a sink. What was the quality of video? How long is the trace between the the source and input of the DP159? Does your GPU apply pre-emphasis to the waveform?

    2. When measuring the DP159 clock output, are you seeing ~150MHz clock output?

    3. When you switch between HDMI1.4 and HDMI2.0, did you disable the GPU data and clock output first, make sure the TMDS_CLK_RATIO_STATUS is being clear/set correctly first, and then enable the output? 

    4. Since you are using the DP159 to level shifting the DDC bus between the GPU and the sink, can you check and see if the GPU supports clock stretching? 

    5. If you toggle HPD_SNK, are you able to get the sink to show the video?

    Thanks,

    Zach

  • 0 in reply to Zach Dryer
    Prodigy 10 points

    Hi Zach,

    Thank you for all the suggestions! I discovered what my issue was.

    My HDMI reference clock calculations had a minor error in them that resulted in the reference clock being a bit off from what the actual clock should be (i.e. the clock was 161MHz when it should've been 148.5MHz). I didn't notice this because all of the lower resolutions / frame rates were working just fine so I assumed the reference clock was correct. However, this was posing a problem with the higher data rates.

    After fixing the reference clock calculations, everything is working correctly now and I am seeing an output for HDMI 2.0 frame rates.

    Thanks for the help!

    Andrada