VOGONS


First post, by dosgamer

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Any hints on how to enable the write back feature on an Intel DX4-100? It's an EW model, so it definitely has write back. Mainboard is an ECS UM8810-PAIO. BIOS is Award 1.23PH (most recent Award) and has options for L1 and L2 write back. Both are enabled, but CPUCHECK still reports write through. I tried jumper settings (https://stason.org/TULARC/pc/motherboards/E/E … M8810P-AIO.html) for DX4 and DX2 write back enhanced CPUs, both settings seem to work fine, but write back is not enabled. The BIOS recognizes the CPU as a "DX4-S CPU" with both settings.

Coppermine Celeron 800 @ 1.12GHz (8x140) - Asus P2B Rev. 1.12 - 256MB PC133 CL2 - Voodoo5 5500 AGP - SB AWE64 CT4520 - Roland SCC-1 - Intel Pro/1000GT - 1.44MB Floppy - ATAPI ZIP 100 - 120GB IDE - DVD-ROM - DVD-R/RW/RAM - Win98SE

Reply 1 of 4, by dosgamer

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So, after spending way more time with this than I should have, I decided to remove the mobo from the case and have a closer look, and this is what I found:

kJQgDOz.jpg

Looks like it was done at the factory. Pin B13 was connected to pin A11. I'll let you guys figure out what the effect of this bodge is.

After desoldering the wire, the CPU is recognized as an IntelDX4-WB and CPUCHK reports write back as enabled. 😎

Coppermine Celeron 800 @ 1.12GHz (8x140) - Asus P2B Rev. 1.12 - 256MB PC133 CL2 - Voodoo5 5500 AGP - SB AWE64 CT4520 - Roland SCC-1 - Intel Pro/1000GT - 1.44MB Floppy - ATAPI ZIP 100 - 120GB IDE - DVD-ROM - DVD-R/RW/RAM - Win98SE

Reply 2 of 4, by quicknick

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Good job! On non-WB processors, B13 is the CLKMUL pin so I think this was done to force a X3 multiplier to whatever CPU this board had previously installed...

Reply 3 of 4, by dosgamer

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Doesn't pulling B13 to ground force an X2 multiplier? Or rather, pulling B13 high (or letting it float) forces an X3 multiplier on AMD DX/2-80 CPUs, I believe. Of course, on WB-CPUs it disables WB.

So the mod could've been done to prevent AMD DX/2-80s from running at 120 MHz which would make them run hot and unstable, if at all ... maybe they forgot a jumper setting to pull B13 low.

Anyhow, this is the same CPU that originally came with this board. I got it as a complete system and the label on the case says DX4.

I could also imagine that ECS decided to disable write back because it causes problems with AMD CPUs, because the AMD implementation of WB didn't work with busmastering, causing problems when writing to floppy and with SCSI adapters, etc.

Coppermine Celeron 800 @ 1.12GHz (8x140) - Asus P2B Rev. 1.12 - 256MB PC133 CL2 - Voodoo5 5500 AGP - SB AWE64 CT4520 - Roland SCC-1 - Intel Pro/1000GT - 1.44MB Floppy - ATAPI ZIP 100 - 120GB IDE - DVD-ROM - DVD-R/RW/RAM - Win98SE

Reply 4 of 4, by quicknick

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You are right, A11 is a Vss pin (and not Vcc as I assumed).