External Cache Diagnostic for 486?

[Uniballer]

I have an MS-4145 VER 1 (PCI 486) board that fails to work right with the external cache enabled. It will boot Memtest-86 V2.8 from a floppy, but fails at the same point every time (15% into the first test). It doesn't display an error message or anything, it just winds up going through the cold boot sequence again, as if the CPU was reset (triple fault?). I have an AM486DX2/80 installed but am clocking it at only 33 MHz. Everything seems to work fine with the external cache disabled.

I tried running CTCM 1.7A and that also resets before telling me anything useful. The CACHECHK V7 program runs through the first 12MB (with noticeable speed improvement on the first 256KB, indicating that the cache has some effect) and then complains about "Invalid Opcode at 0017 0000 3282 3A85 2000 26C7 478B 6502 4489 6508 44C7 000A 2600".

I'm wondering if there is a program out there that would assist in diagnosing this cache problem, or if this kind of problem is even diagnosable with software on this kind of hardware.

 

[Anonymous Coward]

Set your jumpers to 128kb, and remove the corresponding chips. If it still doesn't work, swap the chips with the one you just pulled. This method should work if you don't have too many bad chips. An SRAM tester is probably the best tool for the job.

 

[Uniballer]

Good idea. I tried that, with no success. All the socket contacts look clean and bright. I also swapped the tag RAM with no luck. Then changed the SRAM timing in the BIOS to be as slow as possible, also with no change. Maybe I have a faster tag RAM to try (e.g. 12ns rather than the 15ns used for the data)...

I don't have an SRAM tester, but I do have other boards that could use these RAMs for cache to test with, and that approach would test them at speed.

 

[Anonymous Coward]

12ns TAG on a 486 board shouldn't be necessary unless you're running at 50MHz FSB.

I would test your chips on the other boards as you suggested.