I actually have the exact same problem right now. Did you happen to find any clue about this issue?

the motherboard may require a bios update, remember that the "L2" cache on 486 motherboards is on the motherboard, the processor has nothing to do here

most likely the bios, I have a vlb board with a umc chipset and eveything works with L2 except a 5x86

sKeletoN_SN wrote:

I actually have the exact same problem right now. Did you happen to find any clue about this issue?

Not yet, I had to postpone researth on this matter. This motherboard uses a UMC UM82C482/UM82C481/UM82C206F chipset. I believe L2 not being detected issue is more chipset related than BIOS. I have another MB with exact same chipset, I'll test it too, some time later.

mine is UC4914-G using a um82c491f it detects l2 on a overdrive dx4 100 but not amd 5x86 133 they both have 16k L1 so I don't think its a larger L1 size the problem

Hi I have also run into this problem with a VL486 motherboard with UMC chipset (Stason https://stason.org/TULARC/pc/motherboards/U/U … -486-VL486.html).

Am5x86 133 won't recognise L2 cache. FYI Pentium Overdrive 83Mhz also does not recognise L2 cache (but these are known to have cache comapitibility problems). I have set cache jumpers for 64k, 128k and 256k and it made no difference. Cache chips are Winbond 15ns x 8 and one 10ns (TAG). DX-33, DX2-66 and DX2-80 detect the L2.

BIOS is "IPEX ITG IPX-UM-486IV6201 04/08/1993"
AMI BIOS string "40-0100-001131-00101111-111192-UMC480-H"

I have an EPROM reader and UV eraser. I can provide a copy of the AMI BIOS if this can be modified by someone more intelligent than me?

Thanks all, look forward to your suggestions.

SSTV2 wrote on 2019-08-05, 22:12:

sKeletoN_SN wrote:

I actually have the exact same problem right now. Did you happen to find any clue about this issue?

Not yet, I had to postpone researth on this matter. This motherboard uses a UMC UM82C482/UM82C481/UM82C206F chipset. I believe L2 not being detected issue is more chipset related than BIOS. I have another MB with exact same chipset, I'll test it too, some time later.

Hi SSTV2, did you get a chance to test with your other motherboard with same chipset? If yes, what was the outcome?

I did some further testing and I reduced the bus speed to 20mhz and ran the processor at 80mhz and 60mhz. But still the L2 cache won't detect.

Hi,

both motherboards were tested thoroughly (UM486V and GA-486VM), but neither could detect L2 cache with a 5x86 CPU inserted. I had tried all possible BIOS settings and jumper configurations, related to L2 cache, but nothing could make it work, even tried various BIOS images from chipset-compatible motherboards, including one MRBIOS image - no go. I think this issue is related to the outdated chipset (in relation to 5x86), the UM82C480 was introduced in 1991 for 386/early 486 CPUs, so some incompatibilty can be expected with its cache controller. By the way, this chipset doesn't support WB cache mode, better stick with a PCI supporting chipset, if you wish to max out the performance of a 5x86.

Sorry for the delayed reply, after the forum UI update, I rarely browse here.

Many thanks for your assistance SSTV2. I managed to get my Am5x86 running at 150mhz using 3 x 50mhz. So this somewhat compensates for the lack of L2. It is definitely faster than an dx2-80 with 256kb l2 enabled. Now just need a VLB IDE card capable of running at 50MHz for some extra performance.

I managed to get my Am5x86 running at 150mhz using 3 x 50mhz. So this somewhat compensates for the lack of L2

Am5x86 150-160Mhz without L2 cache is more or less equal to 120Mhz 486DX4 with L2 cache.