After I have implemented a VGA interface on TinyFPGA-BX, 640x480@60Hz, 25 MHz pixel clock,
where it works very nice, I've included it into VIDOR4k.
No hope to have a perfect display, there is a jittering pixel positions.
Well, observed at oscilloscope the HSYNC edge on TinyFPGA-BX is perfectly stable
observing it at 350 us after the trigger (after about display 11 lines from the triggering one).
But on VIDOR4k this jitter is +/- 125 ns which correspond to 125/20 = about +/6 pixels.
Horizontal sync random jitter --> horizontal jittering position because both HSYNC and RGB
timing have the same jitter.
What to do?
I've generated a second PLL for the VGA, trying with slow loop filter and no compensation mode,
both reported as methods to reduce the jitter, but nothing is changed.
I've nuffered the HSYNC and VSYNC outputs to reduce the output current, no changes.
Someone has implemented a VGA on VIDOR4k?