Suppose I wanted to add support for Abit VP6, motherboard that runs a Via Apollo Pro 133A chipset. I found the ISA bridge in this motherboard has PCI ID 1106:0686.
I'm looking at this post Re: YMF744, DOS, no DMA? (PC/PCI, SB-link tests)
From what I understand, things I'm looking for are in 0xAF83 and 0xAF4B in setupds.exe. The original int16s are little endian (as expected in x86 programs), so, originally, int16 from 0xAF83 is 0x2420 and from 0xAF4B it is 0x2410. These device IDs correspond to 8086:2410 (82801AA ISA Bridge) and 8086:2420 (82801AB ISA Bridge) respectively.
0x8086 (written down as 0x8680 due to endianess) occurs in the 3.16 version of setupds.exe a whopping 12 times:
I presume the addresses below 0xB000 are parts of the data structures we're looking for which limits us to just 7 results. The question is, which of those 7 have to do with addresses that hold an Intel PCI vendor ID correspond to Intel PCI device IDs from 0xAF83 and 0xAF4B? I'll keep you folks up to date on this.
edit: OK I dun goofed, this is not where you add VP6 support even if it's not gonna work. The address is 0xAEC0 and you change it to 0x8606 (big endian form of 0x0686, which is the PCI ID of VP6's ISA bridge). Now with this, I managed to ungrey the DMA mode and I can choose between ISA, S-IRQ and INTA# modes for IRQ and I can choose DMA modes between PC-PCI and D-DMA. Since VP6 has no PC-PCI, we need to go with D-DMA. So far, nothing works except for audio tests. Even dsdma.exe is screwed up as it just reboots my computer.
Abit VP6 w/ YT BIOS, 2x Tualatin-S with Connectland northbridge heatsinks, 4x512MB SDRAM PC133 CL2, SanDisk 32GB CF 160/120MB/s W/R, Plextor PX-800A, Voodoo 5500 AGP with passive mod, Voodoo 1, Yamaha YMF724F, D-Link DGE 528T rev B