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How to check HSYNC and VSYNC values on pandaboard

Aashish Patel
Intellectual 690 points

Hi all,

I want to test my display panel on pandaboard. For which I have made modifications to 

board-omap4panda.c

panel-generic-dpi.c

and able to see changes through dvi port. 

I verified the pixel clock and mode setting using

cat /sys/class/graphics/fb0/bits_per_pixel
cat /sys/class/graphics/fb0/modes
cat /sys/devices/platform/omapdss/display0/timings

How can I set HSYNC and VSYNC values for my display and how to verify whether the values I am feeding are set or not ?

I tried looking for a relation between hfp,hsw and hbp with HSYNC and the same for VSYNC but could not find any formula.

Thanks in advance 

  • 0
    TI__Genius 10965 points

    Hi Aashish,

    Take a look at the device TRM specifically section "DISPC Transaction Timing Diagrams"  the graphics there shall clarify the relation . Also take a look at  "DISPC Timing Generator and Panel Settings" after that.

    Regards,

    Boyko

  • 0 in reply to Boyko Kazakov
    Intellectual 690 points

    Hi Boyko,

    Thanks for quick reply.

    I went through those sections they were very helpful, clarified the whole picture for me. Also while going through the driver code (dispc.c) I found out how it internally calculates the HSYNC and VYSNC values from resolution,pixel clock and HSW,HFP,HBP etc. Here is the formula (I simplified it for understanding)

    x_tot = (x_res + hsw + hfp + hbp)
    y_tot = (y_res + vsw + vfp + vbp)

    hsync(Hz) = (pixel_clock)/x_tot

    vsync(Hz) = hsync/y_tot

    I had the Pixel Clock , HSYNC and VSYNC frequency values so I got HSW,HFP,HBP etc values from above formula. (PS : Make sure that values you choose are within the range for you board)

    Now am getting the desired frequencies at output (checked them by probing the pins and also via the registers mentioned in DISPC Transaction Timing Diagrams section). 

    Hope it helps someone who gets stuck at this like I did :)