VIP and NIOS2 don't work together

[Altera_Forum]

Hi group, 

 I am building a small monitor system using D5M and DE2-115.  My current working code is like:  D5M camera -> some processing -> Clocked_Video_Input -> alpha_mixer -> Clocked_Video_Output -> VGA port on the board. Images from camera can be displayed on an external monitor correctly.   Then I tried pattern_generator -> alpha_mixer (controlled by a NIOS2) -> Clocked_Video_Output -> VGA port, and it also works.   Now I am trying to combine these two, which is just to add the NIOS2 to control the alpha_mixer in the first design. And now I cannot see the output anymore. The NIOS2 core did nothing except initiating the alpha_mixer core. I don't know what's wrong with it.  One thing I noticed is that the overflow signal from the clocked_video_input core went high.   Anyone has some suggestions? thanks.

[Altera_Forum]

try to always use the test pattern generator, i think the mixer should have one

[Altera_Forum]

Thanks for the reply, mrbietola. 

 I did try test_pattern_generator. I added 3 channels to the mixer, two were from test_pattern_generator, one were from my VGA data channel. The only thing the CPU did was to switch between these channels according to key press. I can switch between test_pattern_generator channels and display them correctly, but the image of my VGA data channel doesn't display right (I mean a black screen was shown) if I switch to this channel. If I remove the mixer and the CPU, leaving only my data channel in the path, then the image is good again.....

[Altera_Forum]

Try TO add a frame buffer before the mixer

[Altera_Forum]

I'm having a similar problem with a Nios II interfering with a VGA driver that I wrote. The systems are totally independent of one another except for being contained in the same entity. I don't get it. Any thoughts?