First post, by PlaneVuki

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Recently I had a wish to run doom from ramdisk on a 486 mobo without L2 cache chips. (Case4 below)

The mobo is Chaintech 4ULD0 with umc chipset.
(Similar to this one https://theretroweb.com/motherboards/s/chaintech-4uld1)

Here is what happens:
Case1: L2 present + hdd = doom works
Case2: L2 present + ramdisk = doom works
Case3: L2 removed + hdd = doom works
Case4: L2 removed + ramdisk = doom is installed ok but fails to start, freezes on black screen.
(In all above cases setting L2 on/off from bios made no difference).

Why doom not starting in case4 and what can I do to fix this?

I am thinking about cases where fake L2 caches are used, are they just plain empty or do they short some pins of the socket?

Any further required information I can provide.


Reply 1 of 1, by mkarcher

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Rank l33t

I suspect your RAM timings are too fast, and if you have L2 Cache installed, the cache mitigates some access patterns that can not be executed correctly.

Furthermore, I experienced with some UMC 8881 based board, that disabling cache can actually make some RAM patterns execute faster, because the chip set doesn't need to do a tag lookup before hitting RAM. Again, the solution is to set a slower RAM timing.

Lastly, if I remember correctly, I got issues when L2 was disabled and cache timings set to 3-x-x-x, which could be solved by setting cache timings to 2-x-x-x.