Reply To: Trying to make OSSC work with MDA-ish video — won’t sync?

[david.given]

Ah, didn’t see your edit. I did try the low 900s but testing ranges of numbers is very slow (due to a combination of winding the value up and down — the remote control has a number pad on it, wouldn’t it be great if we could use it for entering numbers — and waiting for my monitor to decide to resync). I did find a clock input to the 6544 video controller but I forget the right number, and was down in the single-digit MHz anyway, so it’s obviously being used to generate the pixel clock internally. 16MHz does sound plausible.

Regarding the vsync length issue: I found this in the source code:

define VSYNC_LEADING_EDGE ((VSYNC_in_L ==HI) & (VSYNC_in ==`LO))

This suggests that the OSSC only supports negative sync polarity as it’s looking for trailing edges. That surprises me. I’m aware that what I’m doing is a bit weird, but surely there are other positive sync devices out there? (It’s also possible that if OSSC is trying to lock onto the trailing edge of hsync pulses it’s making it unhappy about detecting pixels. I’ll try inverting both syncs and seeing what happens.)