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frame buffer waitforvsync on interlaced mode (pal) output?

George K
Prodigy 170 points

Hello, 

I have a question on frame buffer ioctl waitforvsync on DM8168 platfrom.

The output mode is set to PAL (720x576 interlaced)

I want to refresh the frame buffer at a rate of 25 fps. 

I use waitforvsync ioctl before calling pan display ioctl.

The number of vsync per second I see is 50. It seems vsync is coming per field.

So, I wait for 2 vsyncs i.e I call waitforvsync ioctl two times before calling pan display ioctl.

Now, the problem is that I am seeing interlaced effect on the output on fast moving graphics.

Ideally I should update the display just before the odd field vsync, so that both odd field and even field vsyncs pick the same frame from the frame buffer.

How can I sync my application to odd vsyncs. Depending upon when I open the fb driver sometimes I see the problem sometimes I don't.

Is there a mechanism in the frame buffer driver to get only odd vsyncs?

Thanks,

George