alexthekid wrote on 2021-05-23, 10:59:
I guess, I'll have to find another Mainboard in order to get a 40MHz System
Well, that sucks, but at least you know that now rather than chasing phantom problems later. I've run some tests to actually see how much BARB affect performance - because it will flush cache on all DMA requests, be it write or read (unlike properly working FLUSH input that should only do that on writes). Which means even on systems with hidden refresh a DMA transfer to SoundBlaster type card to play sound samples is going to trigger it.
I've run Doom2 with -timedemo demo3, with sound configured and ESS688 card being present. These are the results on Cyrix 486DLC at 40MHz:
BARB: 4471 / 20113 / 6348 / 5041
FLUSH: 4471 / 19339 / 6151 / 5042
FLUSH in this case is actually not enabled, just BARB disabled, but unless there is a DMA writing to memory (which on this system could only be the floppy drive and I wasn't using it) it's the same performance. I still haven't gotten around to do the HW mod myself, reason being I actually want to tap memory write signals on SIMM slots directly rather than MEMW on ISA bus, that's because I want to test that for another system where there is no ISA bus.
First number is demo ticks, second is elapsed ticks in full screen (with status bar on the bottom) and normal resolution, third is minimal screen and low resolution, fourth is same as third but with -nosound to validate the idea.
As can be seen there is some performance impact but it's not huge (less than 4%), and Doom2 is playing sounds pretty often. That being said FLUSH should provide smoother experience and would probably affect SXL chips more. In general though I'd say if you experience performance drops with BARB that you can feel while sound is played then the program/game probably needs a way faster 486 CPU anyway.