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Display Driver period

ranchu
Guru 20755 points

Hello,

In HDVPSS user's guide about display driver it is said: "Once the display operation is started, the display driver always retains the last buffer and displays the same buffer continuously till the application gives a new buffer to display."
I would like to ask how this period value is set into the display driver ? Is this the same value for the frame display rate also when this is not the last frame scenario ?

Best Regards,

Ran

  • 0
    TI__Guru**** 477425 points

    Hi Ran,

     

    This is not related to rate, but if the driver does not have any more buffers for the display, it keeps displaying last buffer and since it is displaying the buffer, it retains the last buffer.

     

    Thanks,

    Brijesh Jadav

  • 0 in reply to Brijesh Jadav
    Guru 20755 points

    Hi Brijesh,

    Thanks for the reply. 
    When does the display driver display new frame ? Is it whenever the display link put new frame in queue that the display driver wakes up or does the display driver checks for new frame waiting in constant periodic interval ? what is the rate of displaying the last buffer ? is it equal to the time of displaying this frame (vsync) ?

    Regards, Ran

  • 0 in reply to ranchu
    TI__Mastermind 20245 points

    Yes,

    In call cases frames are displayed at Vsync intervals. At every vsync display driver checks for new frames and if new frames are present it releases old frame.So if new frame is queued old frame is released at next Vsync after the frame is queued.

  • 0 in reply to ranchu
    TI__Guru**** 477425 points

    Hi Ran,

     

    There two, queue and buffer update, are different operations, application call queue from the task context and driver updates the buffer in the isr context, so it does not update the buffer immediately after buffer is queued. All the buffer including the last buffer will get displayed at the display frame rates, how many times last buffer gets displayed depends on the applicaiton delay in queueing the buffer. 

     

    Thanks,

    Brijesh Jadav

  • 0 in reply to Brijesh Jadav
    Guru 20755 points

    Thanks Brijesh,

    And the display frame rates for display you mentioned in your answer is determined according to VSYNC time as hardik said. So if we want to change the display frame rate we just need to change the parameters in the timing command through sysfs ? ( "echo 74250,1280/110/220/40,720/5/20/5,1   > /sys/devices/platform/vpss/display%d/timings" ) ?

    Thanks!

    Ran

  • 0 in reply to ranchu
    TI__Mastermind 20245 points

    Yes,

    You can do that,