theseim wrote on 2020-08-09, 14:05:

By chance I discovered the setting "PCI post Write" in the bios of a borrowed Gigabyte board. With this option activated, the board brought the desired performance, but now with graphic errors under DOS and Windows.

"PCI post write" or "PCI posted writes" is a setting you generally want to have enabled to get decent performance. It means that the chipset buffers (a single, or a couple of) writes to the PCI bus and tells the processor to proceed immediately, while performing the actual write to the PCI bus in background.

If you are getting graphics errors caused by "PCI post write", it might be an interaction with another option. A dangerous option is "PCI write merging" / "PCI write combining". While write merging/combining is a great way to improve performance, there are cards that insist on receiving 8-bit or 16-bit writes and do not perform the intended function if writes to successive addresses get merged to a bigger write cycle. Another relevant option in this regard is "PCI retries". It's possibly for a card to deny a cycle it can not perform right now. Some graphics cards use this feature in response to completely filled write buffers on the card. In the case of a denied request, the cycle needs to be retried later. I could imaging that retrying posted writes needs several setup settings to be in the correct state at the same time.

Another possible source of graphics errors might be insufficient wait states that do not matter if the system is slowed down enough by not having posted writes enables. Try to find an option like "PCI write WS" and increase it from 0 to 1. Or an option "PCI 0WS writes" which needs to be disabled to add a wait state.

Okay, I see. Thanks for clearing that up. Unfortunately none of the boards available to me provide these options in the bios.

Got here:
Asus 8AV-MX (K8M800/VT8251)
Asrock 939A8X-M (ULI 1689)
MSI 7075 (K8T800 Pro/VT8237)

I would prefer to use one of the first two, as they do not suffer from the SATA II bug. But that's beside the point for now. Is there a way to enable PCI post write in the BIOS without having a menu item for it, or otherwise activate it? I have already tried to find hidden options with AFUWIN, but without success. With WPCREDIT I could finally figure out the PCI registers for post write on the Asus board, but they seem to be read-only as they cannot be changed.

Hi again!
Now that I have tested some more things, there are new discoveries. After I got the artifacts described above with my Voodoo 3000 PCI, I had the opportunity to test a V5500 PCI. With exactly the same result! Am I missing something here, or do Voodoo PCI cards in general have problems with "modern" systems? In some graphics modes horzontal lines appear in a noise pattern.

All other expansion cards were removed. In contrast to the first post I noticed that the same horizontal lines appear in the P4 system. I tested an Athlon 64 / K8M800 and a Pentium 4 / 865g system. Both with the same result.

As described above, the artefacts disappear as soon as I deactivate "PCI 1 Post Write" in the bios. But after that I only have one third of the graphics performance. Disabling "0 WS Writes" does not make any difference.

Is this problem known? Are there solutions?

Here a video to showcase the problem...
https://youtu.be/b5M4eeO3KiI

theseim wrote on 2020-10-01, 15:02:

Hi again! Now that I have tested some more things, there are new discoveries. After I got the artifacts described above with my […]
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Hi again!
Now that I have tested some more things, there are new discoveries. After I got the artifacts described above with my Voodoo 3000 PCI, I had the opportunity to test a V5500 PCI. With exactly the same result! Am I missing something here, or do Voodoo PCI cards in general have problems with "modern" systems? In some graphics modes horzontal lines appear in a noise pattern.

All other expansion cards were removed. In contrast to the first post I noticed that the same horizontal lines appear in the P4 system. I tested an Athlon 64 / K8M800 and a Pentium 4 / 865g system. Both with the same result.

As described above, the artefacts disappear as soon as I deactivate "PCI 1 Post Write" in the bios. But after that I only have one third of the graphics performance. Disabling "0 WS Writes" does not make any difference.

Is this problem known? Are there solutions?

Here a video to showcase the problem...
https://youtu.be/b5M4eeO3KiI

This looks similar to glitcher I get on dos on a Voodoo 3, fixed by messing around with mtrrlfbe. Maybe searching in that direction will help, there's other threads on Voodoo 3 graphics corruption on Vogons as well. However, I haven't seen it happen in Windows before.

Thanks Oetker, this is exactly my prolem! In the meantime I found the posts here in the forum...

3DFX Voodoo 3 3000 - Inconsistencies with some DOS and Windows Games
Issue with Voodoo 3 at 320x200

The Windows GUI is not affected, the artifacts just appear in Unreal menues, which I think uses a custom GUI inside the engine. Unlike Windows, they will write directly to a hardware framebuffer.
Okay, then I will have a closer look at mtrrlfbe...