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Video Driver Question on Linux SDK 7.0

JasonHaedt
Genius 3320 points

Hello TI,

I am using SDK 7.0 on the Beaglebone Black and I am struggling on getting the video driver to properly accept my display timings.  I see the HSYNC occurring about 15 pixels after the first pixel of a framebuffer line.  My display resolution is 1366x768P60 and achieved the following settings:

1366x768P60 {

                   clock-frequency = <85860000>;

                   hactive = <1360>;

                   vactive = <768>;

                   hfront-porch = <180>;

                   hback-porch = <200>;

                   hsync-len = <60>;

                   vback-porch = <23>;

                   vfront-porch = <1>;

                   vsync-len = <3>;

                   hsync-active = <1>;

                   vsync-active = <1>;

                };

  • 0
    TI__Mastermind 25235 points

    Hi Jason,

    Please check the output from the "fbset" command to see if the timings are applied properly.

    Also try "fbset --help" to see how to change the display timings.

    Best regards,
    Miroslav

  • 0 in reply to Miroslav Kiradzhiyski XID
    TI__Expert 6715 points

    Hi Miroslav,

    From Jason:

    Yes, I did do fbset on the system and it seems like this is not derived data but is just using the dts file information for this information? 

    Below are the two fbsets.  One at 65MHz and one at 78:

    An additional question:

    When they run the display at 60Hz which means a 78MHz pixel clock the image will shift momentarily on startup a few times.  This happens when the TI ICON bar is loading the system.  If they shift the frequency down to 65MHz which results in 50Hz refresh rate the image is stable and consistent.  However the 50Hz refresh rate is not acceptable for the product configuration.  We did probe the clock and data enable signal and these look correct and stable in both configurations.

    Also:

    Does TI Have any example timings for a 1366x768@60Hz display settings?  We are only able to display 1360 pixels in a line and not 1366.  Hsync is always appearing later than we would expect from the AM335x.

    The settings have been updated in effort to try to solve this issue:

    With the below timings, HSYNC occasionally appears in the correct location.  It seems to toggle randomly, and changes most frequently during boot up.  If I change the clock-frequency to 65000000 (corresponding to a 50 Hz refresh rate), the display appears to be correct all the time.

    1366x768P60 {

                       clock-frequency = <78000000>;

                       hactive = <1360>; //Haedt this never works when we do 1366, the actual active pixels

                       vactive = <768>;

                       hfront-porch = <100>;

                       hback-porch = <105>;

                       hsync-len = <60>;

                       vback-porch = <22>;

                       vfront-porch = <5>;

                       vsync-len = <5>;

                       hsync-active = <1>;

                       vsync-active = <1>;

                    };

    Regards,

    ~John

  • 0 in reply to John Fedak
    TI__Mastermind 25235 points

    Hi John,

    I have asked the factory team for support on this.

    Best regards,
    Miroslav

  • 0 in reply to Miroslav Kiradzhiyski XID
    TI__Expert 3010 points

    Hello,

    1366x768 is not supported by the LCDC since 1366 is not a valid line width for the LCD controller.  The “ppllsb” bits in the RASTER_TIMING_0 cannot be set to the value 1366.  The TRM has more details.

    Regards,

    Josh