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HDMI output shows black border on right on HP L2105 monitor

Carl Blake
Expert 1160 points

I'm having a problem where the HDMI output of the DM8168 displays a black border on the right on HP L2105 monitors.  This black border appears to be the size of the front porch and appears on all video resolutions.  If I force the front porch to 1 then the black border disappears.  I've scoured hdmi_lib.c in arch/arm/plat-omap to see if there's some problem with the code, but haven't noticed anything obvious.  I've discovered that if I set HBIT_2SYNC1 to 1 (which I think is the same as setting the front porch to 1) then the border disappears.  Does anyone know how to fix this properly?

I'm also a little puzzled by the DM8168's HDMI output registers.  There doesn't seem to be anyplace to tell it where SAV occurs.  Typically with HDMI output devices you at least have to tell it the total size of the horizontal line, where SAV occurs, and where EAV occurs.  The HBIT_2SYNC registers will tell it where EAV occurs in relation to the sync, but I don't see anyplace to describe the rest of the blanking period.  There are registers to set DE, but the documentation specifically recommends NOT using DE and the hdmi_lib.c code doesn't use DE.  Does anybody have an explanation for this?

Carl

  • 0
    TI__Genius 12455 points
    Hi Carl,

    The HDMI transmitter will not generate the timing signals, the VENC that is driving the HDMI will generate these. This transmitter simply encapsulates the in-coming video (optionally provides audio) and transmits. 

    If you require to change the timings, please take look at the display timing sysfs entries.


    Thanks,
    Sujith
  • 0 in reply to Sujith
    Expert 1160 points

    Can you explain why I'm getting the black border on the right and why setting the HBIT_2HSYNC register to 1 solves this problem?

    Do you know what side effects or problems I may encounter later because I'm setting the HBIT_2HSYNC register to 1?

    Carl

  • 0 in reply to Carl Blake
    TI__Genius 12455 points
    Hi Carl,

    Yes this register could be used to tweak hSync. I would recommend to change the timings at the VENC rather than in HDMI. Its a good idea to generate the proper timings at the source (one which generates the control signals) than at a place that encapsulates these control signals.

    Updating directly in HDMI might cause issue for other resolutions, as this will be applied to all the resolutions. Since we will update the VENC to generate control signals for different resolutions.

    Thanks,
    Sujith