AMD 5x86 L1 cache mode option in PCCHIPS M919 v3.4 moterboard \ VOGONS

AMD 5x86 L1 cache mode option in PCCHIPS M919 v3.4 moterboard

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First post, by ychh0

Posted on 2025-02-22, 03:54

ychh0 Offline

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Rank: Newbie
Posts: 98
Joined: 2012-02-19, 01:31
Location: South Korea

Hello

I have one system with AMD 5x86 running at 160MHz (40MHz x 4) on PCCHIPS M919 v3.4 motherboard.
There is option to change L1 cache mode in BIOS setup but cannot change. Mine is blocked at Write Back mode with grey colored "Wr-Back" fixed at the option. CPUCHK and other software confirm it runs at WB mode.
I wonder how can I enable this option to change WB or WT mode. Or I wonder if there are any ways to change WB to WT or vice versa in DOS using appropriate software.
In this system, Gravis Ultrasound MAX 2.1 is installed and it loses digitized sounds sometime after playing DOOM. I suspect this is due to L1 Write Back mode since I experienced cracking digitized sounds when running on another UMC881 motherboard wth L1 WB mode (normal in L1 WT mode)

I could find some posts about this subject but I couldn't leave reply at that posts and post a new topic.

Thanks

Reply 1 of 1, by jakethompson1

Posted on 2025-02-22, 04:42

jakethompson1 Offline

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Rank: l33t
Posts: 2033
Joined: 2015-11-17, 04:16

The P24D, Intel DX4WB, Enhanced Am486DX4 and Am5x86 determine whether they will be L1 write-back or write-through at reset, depending on how the system is jumpered. It can't be changed through software.
They actually change their CPUID depending on which mode they are in.
I am not sure why these BIOSes provided an option like this. The BIOS CPUID detection at reset (DX value) should have already identified the mode.

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