VOGONS


First post, by Blavius

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Hello everyone,

I picked up a L40SX this summer. It was cheap and the seller said it was working, however when I got it, it turned out to be a sad mess (quelle surprise). Batteries and caps all leaked and the planar was a mess, it would turn on, but nothing worked.
Anyway, I got to patching it up. After cleaning, recapping, retracing and replacing the Connor drive with a CF card, the thing is working again.

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As I was already way past 'original condition' I decided to see if I could get this slow 386SX to the point where it could rival the 486DX-33 I had in my youth. To do so I got a Ti486SXLC2 from ebay. These are still available, as they are NOT drop-in replacements, they run off 3.3v, while being 5v tolerant on the I/O pins. This means I could not connect the VCC pins to the pcb, but soldered them to an external 3.3V source instead. I don't take pride in how it looks, but to my great surprise it actually worked! To get the most out of the system I changed the oscillator from 40 to 50 MHz, which changes the bus from 20-25MHz. As the processor is clock doubling, it is now running at 50MHz. Be careful, it does get pretty hot at this speed, I'm planning to add a small heatsink to it.

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A lot of the performance gain from this processor comes from the L1 cache (8kb). To get this to work you need to set some parameters using cyrix.exe.
I ended up with cyrix.exe -f -r- -m -xA000,64. The exception address is needed to avoid graphical glitches in windows 95 and DOS4GW crashes in Doom. Doom (low detail) now gets 2935 RT's, instead of 9445 RT's in the original condition, and in Norton it went from 14.4 to 70.4 points, almost as much as the 486DX-33 I was aiming for.

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The Ti486SXLC2 doesn't have a coprocessor and therefor can't run Quake. For this I added an Intel 80387. Here I ran into a snag. With the cache enabled anything using the FPU crashed immediately (quake, speedsys, CPUID). With cache disabled it works fine.
So (finally) here is my question; how do I get the FPU working while having cache enabled? Is there a certain memory range I need to block out to avoid caching FPU instructions?

Also, bonus question, I have been looking everywhere for the external ISA bus accessory to this system(pictured below). I would very much like to install a soundblaster in it and play Command and Conquer. I've tried every seller online that claims to have it, but in the end none do. Please PM me if you have one and would consider parting with it.
L40SX_Communications_Cartridge_Complete.jpg

Reply 1 of 17, by Anonymous Coward

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I remember reading in the mid 90s that there were people having similar issues with TI486 based CPU upgrade kits. It was either clock doubling OR FPU, but not both at the same time. I don't ever remember seeing a solution.

My only suggestion would be to try an 80387SX FPU that is made after 1992 and marketed for SLC/DLC compatibility. I do remember reading some of the older Cyrix FPUs didn't get on well with the SLC/DLCs...not sure about older Intels. Your 387SX has a 1995 datecode, doesn't it?

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 2 of 17, by matze79

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Yes there indeed issues, you should try source a Cyrix 87SLC

https://dosreloaded.de - The German Retro DOS PC Community
https://www.retroianer.de - under constructing since ever

Co2 - for a endless Summer

Reply 3 of 17, by Blavius

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Anonymous Coward wrote on 2021-11-13, 15:03:

I remember reading in the mid 90s that there were people having similar issues with TI486 based CPU upgrade kits. It was either clock doubling OR FPU, but not both at the same time. I don't ever remember seeing a solution.

My only suggestion would be to try an 80387SX FPU that is made after 1992 and marketed for SLC/DLC compatibility. I do remember reading some of the older Cyrix FPUs didn't get on well with the SLC/DLCs...not sure about older Intels. Your 387SX has a 1995 datecode, doesn't it?

Thanks, I wasn't aware there were specific FPU's for the SLC/DLC, thought you could just mix and match. Mine should indeed be from '95, so it would be reasonable to assume the Intel 387's never were compatible. I'll see if I can find something more about that online.

Edit: Ordered a IIT XC87SLC-33

Reply 4 of 17, by Blavius

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Ok, short update. I received the IIT XC87SLC-33 and installed it. As hoped, this one plays nice with the Cyrix, no crashes or other instability whatsoever. Thanks for the advice!
It doesn't really help me play Quake though, it does start now but runs at only a few frames per second (like three or four, you can count them haha). Now, don't get me wrong, I didn't expect this to be fluid in any way, but I do remember playing through quake on my 486DX-33 back in the day and it did run ~somewhat~ playable.

Now that the FPU isn't crashing the system, I could benchmark it.
In CPU-Z vintage there is a benchmark with some helpful references to compare to:

Ti486SXLC2-50 + IIT X87SLC-33 (this laptop): CPU:23.2, FPU:27.4
i486-33: CPU:28.0, FPU:70.0
SXL2-50 + CX83D87: CPU:29.0, FPU:48.0

As you can see the CPU is performing alright, slightly below the mark, but this could be due to the 16bit bus compared to the 32 bit but for the SXL2-50. The IIT FPU I took is clearly slower than the referenced Cyrix FPU. Do these things really differ so much? I though it was only marginal.

In any case, both 387's are dwarfed by the 486 FPU. If Quake is really FPU heavy as it seems (don't know, is it?), this could explain why it runs so poorly on my setup.
Maybe I could boost the system further by finding a fitting Cyrix FPU, but I doubt it's worth the trouble if there is no way to get close to the 486.

Anyway. Does anybody have a tip where I could ask for the L40SX ISA attachment mentioned above? I would love to play at least Doom with sound.

Reply 5 of 17, by pentiumspeed

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Good mods!

Back in the day with my LTE 386s/20 and already has a iit 387 installed, I did exact mod like this except I used Am386sx 25 instead of intel sx 20 and changed oscillator for 50MHz instead of 40MHz made notebook peppy, and best of all, battery run-time remains the same. This LTE 386s/20 did have external cache of 8K made this even faster. Rivaled to Ti 486SLC 25 or 33 with a 1K that one of other notebook owner had.

Get 3 axial yellow ceramic capacitors around 1uF or so 6.3 V or so, hook this to 3.3V around the CPU's pins to nearby grounds, use the solder vias that surrounds the CPU for required filtering couplings. This is required as processors requires this too located very close to their VCC pins. This also increases reliability with math co-processor and overall system.

Cheers,

Great Northern aka Canada.

Reply 6 of 17, by Anonymous Coward

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There are some benchmarks in which the Cyrix 87xLC chips are supposed to stomp the competition, but in real world use you're only going to see a small improvement (if any).
I'm glad to hear that the IIT let you use clock doubling. I'm surprised that an Intel 387 from 1995 would have issues with your CPU.

BTW, adding sound to your setup won't make DOOM run faster. Quite the contrary. I'm surprised you'd even want to play DOOM on any type of SX/SLC machine, much less quake...which really needs at least a 5x86. I only use them for benchmarking.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 7 of 17, by Blavius

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Get 3 axial yellow ceramic capacitors around 1uF or so 6.3 V or so, hook this to 3.3V around the CPU's pins to nearby grounds, use the solder vias that surrounds the CPU for required filtering couplings. This is required as processors requires this too located very close to their VCC pins. This also increases reliability with math co-processor and overall system.

Good tip, thanks. Will add those when I get my hands on a few.

BTW, adding sound to your setup won't make DOOM run faster. Quite the contrary. I'm surprised you'd even want to play DOOM on any type of SX/SLC machine, much less quake...which really needs at least a 5x86. I only use them for benchmarking.

DOOM runs very well right now, to the point where there seems to be some overhead to spend on sound. So why not 😀 Quake was more an experiment to see how it would run, wasn't really planning to spend significant time with it.

Reply 8 of 17, by Anonymous Coward

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What's your DOOM timedemo score?

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 9 of 17, by Blavius

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Right now it's 2935 realticks in low. I'm guessing its also being held down by the video card, not much I can do about that. It does very run well in full screen when I start a new game, not sure how it will behave when it's really busy.

Reply 10 of 17, by Anonymous Coward

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Not really sure how to compare your score. I always do full screen with no sound.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 11 of 17, by Blavius

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I use the PhilsComputerlab package, which has two options for DOOM, low detail and max detail. I previously always ran the low detail as the PC was so slow.
I now ran max detail (fullscreen, no sound) which produced 11039 realtics. Should be 6.7 fps according to feipoa (doom fps = gametics / realtics x 35, where gametics is 2134).

Reply 12 of 17, by BinaryDemon

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I know everyone has a different definition of ‘playable’ but almost no one would endure Quake on a 486dx-33. Is it possible you are recalling that incorrectly?

Check out DOSBox Distro:

https://sites.google.com/site/dosboxdistro/ [*]

a lightweight Linux distro (tinycore) which boots off a usb flash drive and goes straight to DOSBox.

Make your dos retrogaming experience portable!

Reply 13 of 17, by rmay635703

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BinaryDemon wrote on 2021-11-30, 09:12:

I know everyone has a different definition of ‘playable’ but almost no one would endure Quake on a 486dx-33. Is it possible you are recalling that incorrectly?

I know someone who was able to play through quake on a 386dx40

Not sure how they could guess when to fire or where they were , I guess telekinesis is a skill so you can play a guess where based on minimal visual information?

At that point it’s a rhythm game.

Reply 15 of 17, by Anonymous Coward

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11039 realtics doesn't sound like 486DX-33 territory. I haven't benchmarked it, but I would think a DX33 should be something like 4000-5000 realtics, depending on whether or not you have VLB.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 16 of 17, by Blavius

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Anonymous Coward wrote on 2021-12-01, 18:03:

11039 realtics doesn't sound like 486DX-33 territory. I haven't benchmarked it, but I would think a DX33 should be something like 4000-5000 realtics, depending on whether or not you have VLB.

You're right, I had a look at the 'ultimate 486 benchmark' thread and that puts the DX33 at 16.3 fps, more than double. In Norton, on integer performance, my cpu scores equal to the DX33. Assuming that is correct, I would gues the system is severely bottlenecked by something else. Maybe the video card (no idea what it is really) or the memory access, which is only 16 bit on the SX. Not much to be done about that 😒

Reply 17 of 17, by rmay635703

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If you can open up your bios with special utilities
sometimes there are hidden settings for ISA bus divider and wait state settings
you can really open up due to your Pc being a laptop which might help.