Frame latency in OMX chain that includes DSP component

Gabi Gvili

Hi,

I have created an OMX chain that includes capture->dei->dsp->display.
When i am measuring the latency when the dsp is coping input buffer to output buffer (vlpb), the frame rate is 50fps and the latency is 50msec.
When i am changing the vlpb module to perform my (heavy) video enhancement algorithm the frame rate drops to 19fps (which is OK for me) but the latency measured is 350msec. When i enable notify_always as explained in http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/717/t/163085.aspx#603197 the latency is 300msec.
I have 2 questions:

1. If the frame rate processing when the DSP runs at 800MHz is 19fps then the processing time of 1 frame by the DSP is ~53msec. thus i would expect that the latency would be ~100msec, Why is the latency 300msec?

2. Is there anything that can be done to reduce the latency caused by the DSP?

Thanks,
Gabi

over 13 years ago

0 Vimal Jain over 13 years ago

TI__Expert 6535 points

Gabi,

When you give first frame to dsp, does it come back in 53 ms ? If not then either it has not started or needs more buffers before it starts. There could be chances that buffer to DSP is supplied after ~250 ms ? Latency is initial delay , which is different than frame rate.

Regards

Vimal

0 Gabi Gvili over 13 years ago in reply to Vimal Jain

Genius 4120 points

Hi Vimal,

Thanks for your answer, how can i measure the time it takes the DSP to come back after giving the first frame? is it possible to perform time measurements in the OMX IL? How should it be done? please advice.

Beside that problem i have another problem that involves the DSP, OMX chain that includes the DSP stuck in execute state as posted in here

http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/t/166526.aspx#607069

Could you please advice about that as well?

Thanks,
Gabi

0 Vimal Jain over 13 years ago in reply to Gabi Gvili

TI__Expert 6535 points

Gabi,

You can try putting index / identfier in bufferheader->timestamp filed. timestamp field is copied from input to output by omx componnets. So index would travel with the buffer (It is copied from input buffer to output buffer). This way you would know when a particular buffer is received or sent. you could to standard gettimeofday linux api to associate timestamp with each buffer, and log.

Regards

Vimal

0 Gabi Gvili over 13 years ago in reply to Vimal Jain

Genius 4120 points

Hi Vimal,

Thanks for your answer, i will try to do what you adviced when i have time for it, meanwhile, did TI performed latency test with OMX chain that includes the DSP similar to what has been done for capture_encode in here http://processors.wiki.ti.com/index.php/Latency_Measurement_on_Capture_Encode_Decode_Display_Demo?

0 Vimal Jain over 13 years ago in reply to Gabi Gvili

TI__Expert 6535 points

Gabi,

We have not done measurement as your use case, but we have seen frame rate issue when dsp CPU is accessing the data. And DMA alievates the issue.

Regards

Vimal

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Frame latency in OMX chain that includes DSP component