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DM8148 Display Latency

nandish mj
Intellectual 420 points

Hello,

We are using DM8148 with DVRRDK_03.50.00.05. We are using the following pipeline,

Capture(720p@50) --> DEI & Resize --> SwOSD(DSP) --> Display (720x576).

With this pipeline we are seeing a latency of around 190msec. 

In my prints says,

DISPLAY: SDDAC(SEC1): 12 fps, Latency (Min / Max) = ( 255 / 0 ), Callback Interval (Min / Max) = ( 255 / 0 ) !!!

Latency Min and Callback Interval Min numbers seems to be not convincing. 

We are expecting around 100msec.

I have gone through the following links which suggest to implement display ISR which helps to improve 1fps (40msec), but still not close to as expected.

http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/t/282790 

http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/717/p/249459/904005#904005  

  • 0
    TI__Guru**** 475555 points
    Hi Nandish,
    How are you measuring your latency of 190ms? You capture is at 50fps, so capture takes around 20ms, there could be at max 8ms latency introduced by the capture driver. Also display is 25fps, so single frame takes around 40ms. Display could have input queue, if we assume 2 frames, 80ms is introduced by display alone.
    DEI and SWMs should not take mode 20ms, so total latency should not be more than 150ms..
    How are you measuring this latency of 190ms? Regards,Brijesh