TDA4VM: how long does DSS output the camera data

Hi dunpeng,

I guess you mean to get the latency number from capture to display. Multi-cam demo uses VISS, MSC and LDC (if enabled). These modules run at very high speed, so should not much time in processing. Each module should be able to finish in one frame time period, in case they are running in 4 channel mode.. Using this, you can calculate the latency from capture to display..

Regards,

Brijesh 

HI TI:

    so the latency from capture to display is 40ms * N(number node in graph). How to test it ? or can't measure the time.

how to confirm DPI output is camera data? because DPI output black default. I can't get the latency from DSS buffer to DPI output?

Hi wu dunpeng,

ok, there are two questions on this ticket.

1, For latency, one possible way to check it is to add timestamp to the frame and pass it one along with the frame in each node and then at the end, in the display, check the current timestamp and captured timestamp to get the latency.

2, If the output is blank/black, then most likely DPI or capture is not working. Please print the statistics and see which node is not working.

Regards,

Brijesh

HI TI:

  the second question is how long does DPI interface get the dss buffer node? when dss node ready, how to measure the latency from dss node to DPI output

Hi,

As soon as the buffer is programmed in the Video pipelines and DPI is enabled, it will start fetching data from the memory and start sending it over DPI interface.. DSS Node might take one or two frame times before it can configure the buffer in the DSS. So you could consider two frame latency in the DSS. 

Regards,

Brijesh

HI TI：

Brijesh Jadav said:

1, For latency, one possible way to check it is to add timestamp to the frame and pass it one along with the frame in each node and then at the end, in the display, check the current timestamp and captured timestamp to get the latency.

can you give the example code? thanks

Brijesh Jadav said:

So you could consider two frame latency in the DSS. 

so how to measure the latency with code like question 1? 

Hi,

There is no example in the SDK, you would require to develop by modifying existing node. I think capture already puts the timestamp in the descriptor, you would just require to extract it in the display node and measure the latency. 

Regards,

Brijesh 

HI TI:

Brijesh Jadav said:

So you could consider two frame latency in the DSS. 

how to measure this latency?

There is no easy way, because this requires changes in the driver. You would probably have to add new variable in the fvid2_frame and add timestamp in it when the frame is submitted to the HW, programmed in the HW. Then from there, it would taken another frame to get it to the display..

HI TI:

    Is there any refer code? or it's hard do this

Ni unfortunately, there is no reference code available.