I gave the sync signal of Dogyuun a quick run through the scope - I have a gscartsw v5.2 which has a sync-regeneration feature (DIP1 active), which I thought could maybe make it compatible with the OSSC. It doesn't...
Here are some screenshots:
One HSync pulse, direct connection (without sync regeneration):
One HSync pulse, through the gscartsw (with sync regeneration):
Multiple HSync pulses, direct connection (without sync regeneration):
Multiple HSync pulses, through the gscartsw (with sync regeneration):
(
Method used)
I have to state right away that I don't consider myself qualified to give a reliable statement about the cause of the OSSC incompatibility, since I'm still learning much about analog A/V.
However, you can clearly see some relatively nasty distortions between the HSync pulses. What I've observed is that these get stronger with higher signal levels of the three color lines, and they don't get eliminated by the gscartsw's regen feature.
In the intro there's the white "presented by toaplan" screen, and the effect is much more pronounced while it's on screen. I haven't observed this with Tatsujin, which works fine with the OSSC, at first glance I'd say it looks like a design flaw of the hardware.
Whether this is the reason for the incompatibility, I'm not sure, but it stands out the most to me. I'm sure somebody more versed can comment on this though.
T̶h̶e̶ ̶V̶b̶l̶a̶n̶k̶ ̶a̶r̶e̶a̶ ̶l̶o̶o̶k̶s̶ ̶O̶K̶ ̶t̶o̶ ̶m̶e̶,̶ ̶b̶a̶r̶r̶i̶n̶g̶ ̶t̶h̶e̶ ̶s̶l̶i̶g̶h̶t̶ ̶s̶h̶a̶k̶i̶n̶e̶s̶s̶ ̶y̶o̶u̶ ̶c̶a̶n̶ ̶s̶e̶e̶ ̶i̶n̶ ̶t̶h̶e̶ ̶f̶i̶r̶s̶t̶ ̶s̶c̶r̶e̶e̶n̶s̶h̶o̶t̶.̶ Might post a screenshot of it later.
e: Screenshots of the Vblank area:
There's actually a large spike at about 5μs after the falling edge of
every Vsync pulse. Now that could definitely cause problems as well.
Interval between VSync pulses is measured as ~16.88ms (there's some imprecision involved since I dialed it in manually with the cursors), which amounts to a refresh rate of ~59.242 Hz, which is not too odd I guess. Tatsujin has something around 57Hz, if I remember correctly.
MAME however ses Dogyuun at
~59.64Hz, for that I'd have to measure a ~16.77ms interval which seems beyond the slight inaccuacy described above. I don't know where that discrepancy comes from.
maxtherabbit wrote:are yall sure it's the OSSC itself that's "incompatible" and not just simply the display connected to it? OSSC compatibility is usually 100% display dependent
The red LED lights up on my OSSC, signalling that sync is unstable.