15KHz With the nVidia binary driver.

[NightSprinter]

For owners of arcade or multi-scan monitors and nVidia cards, how  hard has it been getting them to display the 15KHz modes?  Apparently a local used game shop is thinking of converting a busted Tekken cab into a MAME box, and I just want to help make things easy for them.

[Ansa89]

I don't know if you can force a 15KHz signal with the official driver (for sure you can't use 15KHz during the boot, since the official driver hasn't the kms support).
You can try to force 15KHz with a special modeline into "/etc/X11/xorg.conf", but in this case the 15KHz will be limited to that X session.
Another way could be trying the nouveau driver.

IMHO the better choice is to buy a cheap hd4xxx or hd5xxx and use the open-source driver.

[MonMotha]

If the hardware supports it, the nvidia binary blob will let you specify 15kHz scanrates.  There is a minimum pixel clock, though, so 320x240p type resolutions may not be usable on most hardware.  640x480i or 640x240p (just do a 2:1 horizontal scale - the output signal is then identical to 320x240) are usually supported.

Some hardware needs the monitor to provide EDID information saying it can support the low scanrates.  The hardware will refuse to do what it's told (!!) without this.  SailorSat was building little dongles for a while that provided the necessary EDID information and plugged in-line with your VGA cable.

Note that not all nVidia hardware supports this stuff.  I've used the 6000 series with some luck, but that's pretty ancient at this point.  The newer hardware is apparently more problematic.  You may also have to use older versions of the driver; I don't know if the newer ones have busted this stuff.

[NightSprinter]

Sorry for not responding back in June, been incredibly busy.  You may be right.  Also, the nVidia Settings application is very picky with resolutions and such (it DID natively switch to a 15KHz 256x240@60p, but only manually due to lack of proper XRandR1.2+ support?).  Odd how I had modelines set in xorg.conf, but games like Rom Check Fail and KoboDeluxe would not correctly switch to them.  Is there something with the binary driver and config file I'm not doing right (and the control panel DID list a resolution below 320x240 as a natively-supported resolution)?

[NightSprinter]

  I'm actually getting somewhere.  Putzing around with a 768MB GeForce 8800GTX, and managed to get some modelines working.  Following that, I was able to get my two preferred resolutions for Kobo Deluxe (15KHz 320x256 50Hz, and 15KHz 640x512@50i).  Even a custom resolution generated by switchres for a 3:4 horizontal aspect in Donkey Kong worked when using switchres.  This is where some issues still apply for GroovyMAME/GroovyUME:

The old XRandR methods are apparently being used here.  I believe instead of something like "256x240x60.00", XRandR 1.2 and later now require modeline names to use an underscore instead of a second 'x" ("256x240_60.00).  This does also happen with WINE, as I'm not sure how to get that to work (as wine requests some really oddball stuff.  Try using wine with Cho-Ren-Sha X68k as an example).