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Timers vs VPort, How can time stop during image capture?

Peter Csakany
Prodigy 110 points

Hello,

 

Background:

I have a DM648 EVM I compiled and run all the demo application and now I am making my own. The system seems running fine and all the configurations check out.

 

Problem:

I capture a single sd steam using the  VPORT driver from dvsdk 1.11 and pspdriver 1.10 with BIOS 5.40.02.22.

I get the frames OK but the time stamp are odd as i can get a full PAL frame every 25ms.

 

Investigation:

  1. I run a loop for 10 sec to check that the BIOS low resolution timer is counting with 1ms a tick as configured. It is. teh time on its own works fine.
  2. I used an alternative timer to see whether there is a BIOS problem with the timer slowing down during capture. I timed the frames myself. The jitter is a few ms larger but the frames are still coming in 25ms intervals.
  3. I captured 1000 frames and measured how long it takes. It took 40 sec, but the timers shown that only 25 has passed.
  4. I used the MiniDemo application shipped with the dvsdk to see that the same problem arises. It did NOT! Compared BIOS configs and the code line by line. The only difference seems to be that the MiniDemo allocates new buffers to replace used one whilst I re-queue the old ones.

 

Question:

If the capture is working fine as the test suggest it is, why are the timers slowed down? Since they are HW counters run by a derivative of the system clock VPORT should have no effect on them. What is effecting the timers in my code and not in the MiniDemo?

 

Your help will be greatly appreciated.

Peter