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MTRRLFBE issues encountered. Possible fix?

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First post, by mattrock1988

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So I am *finally* back in the game again with yet another vintage PC build, based on a Mendocino Celeron, Nvidia GeForce 4 MX 440, 256 megs of RAM, all running on top of SvarDOS (DR-DOS) and it’s been quite the dream so far.

However, I have noticed one issue. Whenever I enable write combining for LFB modes using MTRRLFBE, I either encounter hard crashes or periodic split-second garbling of my display before everything looks normal again. I don’t notice these issues if I run my games without write combining.

The games I tested in question are FastDOOM and Quake, both running at 640x480 resolution. I’m wondering what kind of problem I’m facing? I tried changing DPMI hosts from HDPMI32 to CWSDPMI, changing out sticks of RAM in my box and running Memtest86+ to verify the memory’s functionality and integrity, and ran this on different DOS versions, like MS-DOS 7.1. Are there any other possibilities to consider?

Retro PC: Intel Celeron Mendocino @ 500 MHz, TYAN Tomahawk BX, 6 GB IDE Quantum Bigfoot, 256 MB SDRAM, DVD-ROM, 1.44 MB floppy, Nvidia GeForce MX 440 AGP, ESS AudioDrive 1868F ISA

Reply 1 of 3, by auron

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what happens if you set write combining from BIOS instead, or use fastvid?

as for the split-second graphical glitches, IIRC it's explained in the quake technical readme that this can be due to it using page flipping without vsync, and suggests that toggling vsync on fixes this, with the usual downsides. i suspect the same thing is going on in duke3d as i've had similar issues in that game.

turning off the LFB can also sometimes fix these issues - forgot if quake lets you do it via console but if not, use NOLFB. this will reduce performance though.

Reply 2 of 3, by mattrock1988

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Huh… write combining can be done in the BIOS? I never heard of this. Is this more common than I think?

I’ll test out FastVid.

Retro PC: Intel Celeron Mendocino @ 500 MHz, TYAN Tomahawk BX, 6 GB IDE Quantum Bigfoot, 256 MB SDRAM, DVD-ROM, 1.44 MB floppy, Nvidia GeForce MX 440 AGP, ESS AudioDrive 1868F ISA

Reply 3 of 3, by auron

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it was a thing starting with 440FX, not sure if any of the older chipset socket 8 boards ever got it.

additionally, some BIOSes have seperate options for banked VGA and LFB - in my experience banked VGA transfer rates were still low after activating everything in BIOS, so fastvid can still be useful there. it's explained in the fastvid readme that the BIOS options use more conservative settings.

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