CVO underflow problem in QSYS

[Altera_Forum]

hi,  

 I'm using the CYCLONE III development board inorder to set up a VIP system in QSYS, where I'm mixing two video streams using the alpha blending mixer and clocking the 1280x800 video stream @ 60Hz out to screen.   When I download a SW application to the NIOS II and only activate the first layer (640x480) in the mixer, I'm able to provide video output to screen, however, when I try activating the second layer, the screen goes blank, and I can not deactivate the second layer and get the video chain up and running again. I seem to be getting underflow for the CVO.   The 2 input video streams are composite 4:2:2 720x576i, and they are processed in QSYS as follows :   CVI (720x576i) -> CLIPPER(640x480i) -> COLORPLANESEQUENCER -> CSC -> DEINTERLACER -> MIXER, and the 1280x800 background layer is provided by an TESTPATTERNGENERATOR.   I think I should have plenty of memory bandwidth on the Cyclone III for my application, as I don't have extensive memory usage in the design. I'm using tripple buffering for the Deinterlacer while using the bobscanline interpolation for the 640x480 formats, so the deinterlacers are only using a single read/write master each. The memory interfaces are running at 75MHz (half rate) , using 128 data width.   I tried placing the Deinterlacers on different external memories, but that did not seem to help either, as I still get the underflow. Are there any step that can be done to solve this issue ? Shoule I increase/decrease anything with regard to the pipeline stages and the burst sizes ?