Looking good indeed.
I don't think this chipset can tick reliably at 40mhz with 0 wait-states.
You need to be at 33mhz for that.

megatron-uk wrote on 2021-05-16, 17:44:

Ok, playing around with memory sticks now - swapped out my 4x 4MB 60ns 'known working' set and fitted the 8x 70ns 1MB parts that came with the board. It's not happy at 0ws any more due to the slower parts, but at 1ws it runs fine, the memory throughput is ~1MB/sec faster (some sort of interleaving between banks?) and the Doom test runs.

I found Doom timedemo to be an excellent test for too aggresive WS settings - on both cache and memory. So if it hangs/crashes, your settings are not actually fully stable. BTW some mobos prefer to have both banks populated and will enable interleaving, that also gets you a bit of performance improvement. And then there are L2 cache limits, sometimes as low as 16MB, so on these 386 mobos the sweet spot seems to be 8x 1MiB.

Now your 3Dbench and Doom scores are consistently higher than mine, and It'd expect that with overclocked ISA bus. So I think you're just about at the limit now. Just FYI I get 1847 and 6867 for Doom on 8MHz ISA. and for Quake 320x200 timedemo it's 969 frames 397.0 seconds 2.4 fps with Cyrix CX-83D87-40-GP FASMATH - in case you want to compare that co-processor of yours.

Thanks, @pshipkov, @Deunan; it does feel like I'm at the point of diminishing returns now. If I could find an SXL-40 I'd like to try that, but they seem to be silly money compared to the DLC-40 so I'm not in any hurry to do that; I'm also not particularly interested in the clock-doubled parts so if I can't track one of those SXL-40's down then this config will be the limit for me.

All SXL(C) parts have clock doublers. The SXL-40 can work at 40MHz or 2x20MHz - obviously the 40 is better because of faster bus though. You can still use it in older 16MHz system and enable clock doubler to get 32MHz for example - and that's where they shine.

It's not all that much faster then 1KiB DLC clock for clock though, most likely due to the lack of burst mode on 386 and thus any replacement - all memory loads to populate L1 take twice as long as on real 486. Some programs might benefit more than others but the usual benchmarks don't show much improvment. Doom is 1768 / 6365 and Quake is 969 frames 380.8 seconds 2.5 fps. You'll get about 1fps more in 3DBench vs a DLC.

Yes, from reading the various threads about the SXL I figured it's only around 5% faster on average.

I managed to go back and redo all the benchmarks for Doom, using the various Cyrix cache tuning options, as well as the two processor types and bus speed options:

Here's the raw numbers for the Doom timedemo results:

A couple of observations:

1. The Am386DX-40 really doesn't benefit much from the ISA overclock to 13MHz; in Doom it is clearly the processor that is by far the most restrictive element.

2. DLC going from cpu cache-disabled to the default cpu cache-enabled setting results in a 12% improvement in Doom low-detail frame rates and 13% in high-detail.

3. DLC going from cpu cache-disabled to the most optimised cache-enabled setting results in a 17% improvement in Doom low-detail frame rates and a staggering 35% improvement at high-detail.

4. Boosting the ISA clock from 10MHz to 13MHz with the DLC brings just a 1% improvement to Doom low-detail frame rates (to be expected, since we're not pushing many pixels!) but more than 6% in high-detail.

5. From non-optimised cache-enabled settings to most-optimised shows gains over just under 5% in low-detail modes and 19% in high-detail Doom timedemo results. Who wouldn't want a free 19% of extra performance!

Short video capture of some of the benchmarks:

https://www.youtube.com/watch?v=1q0klV9o15I

I'm still trying to work out the most optimal way of uploading Dos captures to Youtube, evidently videos uploaded in the native 640x400@70Hz are not what it wants and get squashed down into 360p@30Hz blur-o-vision. I might have to try integer scaled 2x captures to see if the upload retains a better representation of the video.

Capture route is:

VGA ->
OSSC [passthrough, cleanup, no scaling, no scanlines] ->
OBS + Magewell Pro Capture HDMI (RGB888, no resolution conversion, no framerate conversion) ->
Nvidia NVENC encoding (high quality preset)

Can you add black bars on top and bottom to bump the vertical resolution to 480? I think it will try to match the closest otherwise and it's 360p, which is also pretty bandwidth starved and blurry. Static single-color bars cost next to nothing on modern video codecs. Though I'm not sure if YT supports 640x480 in 60Hz, you might have to upscale to 720p for that...

This system has the potential of 45 or 50 mhz.
Give it a go.

Small update on this system - I bought a set of 8x 60ns 4MB memory modules from Tiido from his sale on Amibay... although the board recognises them for a total of 32768KB and I don't get any errors in any of the memory checking tools that I've ran, I'm back to Doom not starting again.

For some reason, when using 4MB modules (either my originals or the new ones I've just bought) Doom will not start on this board. Go back to 1MB modules (without changing anything else) and it starts straight up.