sofakng wrote on 2022-10-24, 22:15:

OK - I'm trying to run VGATV on the "weeCee" (Volaris Z9s chipset) and it detects the chipset as Tseng Labs but it the OSSC reports the signal as 263p (31.54 kHz, 119.93H) (using NTSC command-line option).

If I try to play a Sierra game (ie. PQ1 AGI), the OSSC can't sync. The OSSC LCD flashes between 263-p (63.08kHz 239.86Hz) on/off (but no video signal is sent).

Is the source for VGATV available?

Obviously you are getting twice the rate you are supposed to get. This might be due to a hardware limitation for games using a 320x200 mode. A standard VGA card run at 12.6 megapixels per second, which is fine for 320 pixels 31.5 kHz or 640 pixels at 15.7 kHz, or it can run at 25.2 megapixels per second, which is fine for 640 pixels at 31.5 kHz. For 320 pixels at 15.7kHz you would just need 6.3 megapixels per second. A standard VGA card doesn't provide that clock, so either VGATV needs to do some magic, or it will only work with 640-pixel modes.

on "most" VGAs that work with the TSR, it works fine with 320x200 games (I assume by pixel duplication)

mkarcher wrote on 2022-10-25, 18:13:

For 320 pixels at 15.7kHz you would just need 6.3 megapixels per second. A standard VGA card doesn't provide that clock, so either VGATV needs to do some magic, or it will only work with 640-pixel modes.

In 256 colour mode the VGA outputs a pixel every other clock, right? So that plus the standard CRTC divide-by-2 option should be enough to achieve the required 6.3Mhz dot clock...

kdr wrote on 2022-10-25, 20:16:

mkarcher wrote on 2022-10-25, 18:13:

For 320 pixels at 15.7kHz you would just need 6.3 megapixels per second. A standard VGA card doesn't provide that clock, so either VGATV needs to do some magic, or it will only work with 640-pixel modes.

In 256 colour mode the VGA outputs a pixel every other clock, right? So that plus the standard CRTC divide-by-2 option should be enough to achieve the required 6.3Mhz dot clock...

Yeah, that's correct. But I wouldn't be surprised if the Sierra AGI games mentioned in this thread use the EGA 16-color mode, which already use the standard CRTC divide-by-2 option to get to 31.5kHz.