Problem with Pixel Buffer DMA Controller back buffer

Hi

I have successfully instantiate the Pixel Buffer DMA Controller university program IP core in QSYS and i was able to display the .BMP file on the screen

but the problem is when i'm writing to the back buffer and VGA is displaying the default buffer, the video output get flicker.

It happens always when i'm writing to the back buffer even when i don't want to swap the buffers

I tried another scenario, the default buffer display green box on the screen and everything was well, but when i write some dummy data to the back buffer the VGA screen starts flickering

the Pixel Buffer is using SDRAM

Please give me suggestion

Best Regards