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Graphic stutter in FPS, but only with sound/music enabled (on PKM-0033S/GMB-486SPS)

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First post, by donny

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Hi there,

I have an specific issue which I didn't find discussed in the past, please bare with me 😀

Situation:
- MS-DOS 6.22
- 486 MoBo ISA+PCI (DTK PKM-0033S aka GMB-486SPS)
- 128kb Cache
- CPU AMD-X5-133ADZ
- 16 MB FPM RAM
- CF-Card
- S3 Trio64 on PCI
- ES1868 based SB ISA

Game:
- Doom 1 Original (or Fdoom 0.9.9f)

Issue:
If Sound and Music are enabled, certain moving actions produce graphic stutter. (-> Like turning ones-self around own axis)
But: If sound/music is disabled, everything is fine whatever I do (or move).

The setup itself seems more than sufficient for the Game. Fdoom Benchmark in Demo1 hits the 35fps ceiling easily.

I tried some obvious things / thing I know from the past:
- Changing IRQs / looking for conflicts -> No change
- Fiddling with some BIOS settings like ISA-Clk, Cache, etc.
- Read about MPU-401 issues that may cause this -> Disabled MPU401 with "esscfg.exe" -> No change
- Univbe -> No Change
- Bare DOS without loading anything (F5 at start-up) -> No change
- playing around with "mode con rate=" as someone suggested to me...

What I'm looking for are more ideas on how to diagnose - and - best case - avoid this issue 😀

PS: If I remember correctly I even had Pentium 1 setups (133 MHz) in the past which had this issue. I simply didn't bother back then.

Thanks in advance.

Greets,
Sebastian

Reply 1 of 4, by auron

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my guess would be the CF card, since that's the part that's not period correct. would try either smartdrive if you haven't, or try installing win95b and see if the issues persist after enabling DMA on the CF and running the game under windows.

also you probably can't expect an always locked 35fps on anything under a p100, even for doom 1. when i tested the game on a p60, there was quite noticeable stutter once a couple of spectres were on the screen.

Reply 2 of 4, by donny

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Thanks for your quick response, thats nice input! Will try that. And for sure back in the day one was probably also more forgiving regarding FPS, stutter etc - but my memory is cloudy... 😀

Reply 3 of 4, by auron

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to correct myself, i don't think any 486 chipsets actually offered support for ATA DMA, so that's really only relevant if you chose to connect the CF to a PCI controller. but nevertheless, windows 95 still offers 32-bit file+disk access that could be worth a comparison.

and also, i'd suggest to actually try some heavier doom engine content, such as the larger maps in doom2 or the master levels. turning sound and music off, you could see if the results you get are any close to what you described for doom 1 with sfx+music. if so, that would perhaps hint at a performance overhead from those.

Reply 4 of 4, by Jo22

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MultiWord DMA might work on ISA bus, even, though.
Late E-IDE controllers for ISA bus had this feature and included an BIOS. Example: Link
Haven't seen that for ages, though.

https://en.wikipedia.org/wiki/WDMA_(computer)

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