HD3800 + CRT Emudriver: fuzzy video for resolutions below 344x256

[andreino11]

Hi all. First of all, a huge thanks for having developed CRT Emudriver and all the associated tools, they are really amazing.

I write because I'm experiencing a weird issue after generating video modes with VMMaker 1.3c.

I have a Windows XP based PC with an ATI Radeon HD3800 connected to a 15Khz arcade monitor (branded Selti, see attached photo). I currently run MameUI32 0.146 and I generated all the modelines based on that executable. The modelines.txt file that I got is also attached to this post. Most of the resolutions look great, but I have 2 problems:

- Practically all the interlaced resolutions had to be fine-tuned to almost eliminate a very heavy flicker which was due to a wrong V-center value (not a big problem)
- Any resolution below 344x256 @ 58p isn't working. I get a fuzzy image as soon as I try to switch to them. 344x256 works great, though, and the image quality is superb. Other than all the lower resolution, also 368x240 @ 60p is suffering of the same "bug".
- Also, the specific resolution 336x256 is causing a blue screen and an immediate system reset.

Please note that I'm not even talking about using them with MAME, I'm just simply using ArcadeOSD to test them.

I generated the modelines without touching the VMMaker.ini file, so all the values contained there are the default ones. Is it something I can fine tune on the software side or is it due to a hardware limitation of the graphic card?

A sincere thanks in advance to anyone who will help me.

[Calamity]

Hi andreino11,

This is a well known issue that affects some models of the X series, and all models of HD 2xxx and HD 3xxx families. They can't do low dotclocks using Windows drivers (they behave well under Linux however).

The workaround is to set the DotClockMin option to around 8.0 (MHz), both in vmmaker.ini and mame.ini in order to create double width modes for the required resolutions.

When used with GroovyMAME, this trick produces absolutely perfect results without video artifacts of any kind.

[andreino11]

Hello, thanks a lot for your answer.

I re-ran VMMaker as you suggested, now I have all the double width modes you were talking about.
I also got rid of MameUI32. I installed the newest groovymame version and I'm currently running it via the MaLa 1.74 frontend.

Now, all my favorite games look great... on-the-fly modeline calculation works flawlessly.

I still have to try vertical games and adjust the centering for some of the resolution, but the result is indeed far above my expectations.

Thanks again and keep up the great work!