Vsync advice needed

MrClump · Jan 31st 2022

I can only get vsync to work with my MK3 if I select "Auto Resolution" in the VGA mode. This works fine, but rather than receiving a full screen 1280 x 1024 image my monitor instead says it is getting 1280 x 512 and so is having to do a vertical stretch. If I enable vsync without using auto resolution I just get a black screen, although I did manage to get to a point where an image would occassionally display by adjusting the pixel clock a bit. Auto resolution works fine, it just doesn't look quite as nice due to the vertical stretch from the monitor, plus I lose some of the scaler features such as filtering of course.

I am using a BenQ BL902 which according to the specs only supports 60Hz, but is generaly quite happy with 50Hz too as I also use it for various other devices at 50hz with my OSSC. I have the same issue whether I use 50 or 60Hz.

Am I doing something wrong?

My monitors EDID is read as follows:

Pixel Clock 108000000

Horozontal Timing:

Visible: 1280

F.Porch: 48

Sync Len: 112

B Porch: 248

Polarity: Pos

Freq Khz: 63.9810

Verical Timing:

Visible: 1024

F. Porch: 1

Sync Len: 3

B. Porch: 38

Polarity: Pos

Freq Hz: 60.0197

Jens · Jan 31st 2022

Just switching VSync on doesn't do the trick - you need to have an output screen mode that is near 50Hz already. The way the VSync works on Indivision is that the output stage will insert blank lines at the selected line frequency until the host machine does a VSync. So in order to get to a compatible mode, please generate a 50Hz mode first, make sure that it's displayed properly, and only switch on VSync if your output is *slightly* faster than 50Hz. Only then you can expect it to work - but it's still not certain, as some monitors don't like the different numbers of lines of each frame that the method produces. Some will display flickering black lines at the bottom.

MrClump · Feb 2nd 2022

Thanks. It looks like my main monitor doesn’t like vsync on unless it’s with auto resolution. I tested a every increment up from 50hz up to around 52hz with no joy.

I tried a portable hdmi monitor and almost got a stable vsync image, with occasionally dropping out.

I have another couple of monitors in the attic, I might get them down and try them at the weekend.

lovely bit of kit though, I am really enjoying the super crisp display.

MrClump · Mar 6th 2022

I fetched my BenQ BL912 monitor from the attic, and perfect vsync at 50hz! Pinball Fantasies is now buttery smooth.

I guess the BL902 just didn't like it.

turrican9 · Mar 6th 2022

Bl702a and bl912 are known to work great when connected directly to rgb or supporting vsync from the range of indivision scandoublers. Also works with tc64/tc64 v2 with vicii sync and any other cores i've tried.

Jens · Mar 7th 2022

Maybe not all monitors of the same "type" really have the same firmware? Especially for non-advertised features, I'd always look at the individual unit, not just the type number.

turrican9 · Mar 7th 2022

MrClump tried a bl902 which i don't know anything about. But his bl912 did indeed work with vsync. So far i haven't heard of any bl702a's or bl912 not working with vsync. But yes, what Jens said is a good point

MrClump · Mar 7th 2022

Correct they are two different models with different firmwares, the menus are quite different on the two; plus the BL912 of course works with 15khz VGA and the BL902 does not.

Anyway, I am now very happy! I do have one very, very minor issue I may need to ask about but want to do some more research first.