First post, by Blavius
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.
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.
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.
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.