PS/2 SUCCESS! - I am now working on integrating the PS/2 circuit onto the motherboard in a discrete manner. Unfortunately, there is only one inverter free on the 7406 so I'll need to use a second 7406 inverter package - EDIT, actually, you can cut the pins off the onboard one and use a single inverter package.
IRQ12 was the missing link. Thanks to NJRoadfan for thinking of this! I'll need to find a clean way to integrate the extra inverter IC and PS/2 header onto this board somehow.
Now if only I can figure out how to get IRQ15 routed to the 4th PCI slot. Seeing how the secondary IDE controller doesn't seem to work, IRQ15 should be free. Is there a particular HEX address in the BIOS which controls the PCI IRQ routing table?
EDIT1: IRQ15 is indeed free. I can use the VGA controller on IRQ15 by setting the PCI priority order. So my remaining task for this board is to somehow inject a 4th PCI slot into the BIOSes routing table and call it device number 9, as was the case for the original DTK BIOS.
EDIT2: The original DTK BIOS with the Modbin mod "enable PS/2 mouse" also works with the PS/2 mouse. PCI slot 4 and Secondary IDE controllers also work fine. The problem with the original DTK BIOS is that it doesn't work with 64 MB SIMMs. And using 4x32MB SIMMs is unstable at 40 MHz. It does fine with 4x16MB SIMMs at 40 MHz, but I am set on getting a 486 board working with 128MB RAM, 1024K-WB, PS/2, 4 PCI slots, and stable at 40 MHz w/fastest timings. So far I can achieve all of this, except only 3 PCI slots when using the hacked 4DPS-v1.72 BIOS on the DTK board. I figure modding the 4DPS BIOSes IRQ routing table for the 4th PCI slot would be easier than figuring out how to add 64MB SIMM support to the DTK BIOS. Note that the manual for the Gemlight board (GMB-486SPS) mentions this board supports 2x64MB SIMMs. The DTK PKM-0033S board I am using is supposed to be the same as the GMB-486SPS. I wonder if the BIOS files for these two boards were programmed differently? Anyone have the BIOS image from an official Gemlight GMB-486SPS branded board instead of the DTK branded board?
EDIT3: I figured out why the 4DPS BIOS doesn't seem to work with the second onboard IDE port on the DTK PKM-0033S. I just realised that the DTK board uses a Winbond W83769F chip as its IDE controller, whereas the 4DPS board is using the SiS 496 as the IDE controller. Here's a quote from the SiS datasheet,
The built-in IDE controller of 85C496 acts as a VL-target, all control pins to IDE-drives are shared with PCI AD bus.
Due to this restriction, IDE cycle and PCI cycle cannot be executed concurrently.
But DTK's onboard primary IDE channel still seems to function with the 4DPS BIOS.
Something else of concern in the SiS manual,
85C496 supports VESA VL-bus standard target interfaces. To enable VESA target cycles, register 57[3] must be set to
enable the LBD#, LRDY# pin. Note that if VL bus is employed, then 85C496 supports only three PCI masters instead
of four.
Does this mean that even if I manage to copy the IRQ table from the DTK BIOS into the 4DPS BIOS that I still can only use 3 PCI slots?
Perhaps it is best to adapt only the aspect of the 4DPS code which allows for the use of 64 MB SIMMs and inject this into the DTK's BIOS. Does anyone have any idea how to do this? 4DPS v1.72 BIOS uses AWARD 4.51PG, DTK uses AWARD 4.50PG.
Alternately, does anyone know of another SiS 496/497 motherboard which has 4 PCI slots, 1024K cache, 0 VLB slots, and uses a Windbond W83769F as the IDE controller?
Much appreciated!
EDIT 4: Has anyone ever found the assembly language source code for BIOSes? Alternately, does anyone know someone who is familiar enough with machine code of the BIOS to reverse engineer it, or in the least, know how to add 64 MB SIMM support to the DTK BIOS? I wonder if the sheer act of updating your BIOS from AWARD 4.50GP to AWARD 4.51GP is enough to enable 64 MB SIMM support. Anyone know how to do this?
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