Buffer Overflow and Underflow in Clocked Video Input/Output

Hi Faisal,

In one of the first replies, vgs mentioned the fact that the CVO clock needs to be derived form the CVI clock and if it is not, you need to use tripple buffering with frame dropping / repeating enabled. I did not see any reply indicating if you have tripple buffering enable. If the output clock (driving the CVO) is not derived from the video input clock, the output frame rate will never match the input frame rate and you will get underflows / overflows no matter how large you make the FIFOs. If you cannot derive the output clock from the input clock you have to periodically drop or repeat a frame (as would be done by a tripple buffer).

From your diagram it looks as if only the first CVI gets the actual video input clock and all subsequent CVI and CVO gets clocked by your local 148.5MHz. As a test, just enable tripple buffering and frame dropping / repeating on you first framebuffer. If this makes the problem go away, then you know it is due to the different clocks.

Regards,

Niki