AGP slot on Trigem Lyon mainboard

[Zare]

This is 440BX mobo that has integrated ATi card - https://theretroweb.com/motherboards/s/trigem-lyon

There are no jumpers to turn it off. If there is another graphics card in the computer it goes off automatically.
My problem is I'm unable to get MX400 AGP card to run consistently.

To make the convoluted story simple, start with Debian Etch. I configure the nvidia driver, but when getting to X I just get a mostly blank text mode screen. The X is running and the computer is operational, so going to another tty and checking the X log I see the nvidia driver failing to initialize AGP over nvagp, I switch to agpgart, same no-go, I disable AGP access and then I don't get X "booted" due to nvidia driver stopping it because there is no IRQ assigned to graphics card.

In the system bios (AMI that looks like Win3.11, not much options there), I can tweak "IRQ assigned for PCI graphics card". This obviously reflects to AGP port, and now I can run nvidia under Debian and 3D works but the card is in PCI mode.

For Win95 I had to pick one particular driver version (45.something), and install it before anything else. I think what was relevant here are the mainboard drivers - the successful nvidia install was done without them. The card takes IRQ 11. dxdiag says AGP texture acceleration enabled and the test runs smoothly. hwinfo says AGP 4x (disabled). If the card is moved to another free IRQ it will again fail to come up - depending on IRQ, either blank text mode screen while Win continues to load, or a reboot.

On Win2000 installing the same driver version as first thing, it's again stuck in text mode on reboot. Blank screen with cursor while I can see on the HDD activity that the OS continues to boot down to the desktop.

I can see possibly issue of no true AGP slot, and IRQ handling.
At this point I would be pleased to have it running in Win2K in PCI mode. It is my understanding, that if AGP is really PCI, the drivers will just fall back. There are no failures like this.

 

[GiGaBiTe]

The AGP bus was never designed to accommodate more than one device on the bus at the same time, and the 440BX chipset was certainly not designed to do it either.

Unless there's a proprietary ASIC somewhere on the board that can do a complex switching operation, the "AGP slot" is really just wired to the PCI bus, and the AGP card will only work in very slow PCI mode.

The compatibility issues you're experiencing are certainly related to that. The drivers are expecting an actual AGP device and are looking for it in the wrong location. AGP Texturing doesn't actually require the AGP bus, it will work on PCI, because all it is really doing is parasiting system RAM for texture storage when the dedicated video memory on the video card is depleted. It will be a whole lot slower though, because it has to share the extremely limited PCI bandwidth.

 

[Plasma]

I can see possibly issue of no true AGP slot, and IRQ handling.
At this point I would be pleased to have it running in Win2K in PCI mode. It is my understanding, that if AGP is really PCI, the drivers will just fall back. There are no failures like this.

Do you have any PCI cards installed? If you are also using the first PCI slot it could be an IRQ sharing problem.

 

[Zare]

@Plasma I have a 3Com NIC but it is below.
@GiGaBiTe Then that's that, definitely. Watching some people do stuff with P4s with integrated graphics I wasn't under the impression that the drivers will fail in many cases.

Is there a registry key to force AGP off on nvidia drivers for Win2K, like Option NvAGP in X config? Maybe disabling the system AGP bridge in 2K before installing the driver could force it to PCI mode like I see on Windows 95.

 

[GiGaBiTe]

There might be some ini or registry entry that can do it, but I haven't dug that deep into those old drivers in decades. Worst case, you'd have to be modifying the driver DLLs directly.

 

[Zare]

Disabling the CPU->AGP bridge in Win2K just disables the graphics card access altogether, no driver shown in dev mgr, "VGA" in display applet.
Fortunately there are registry settings that work under this 45.23 driver version, in HKLM\SYSTEM\CurrentControlSet\Services\nv\Device0 I added EnableAGPFW 0, EnableAGPSBA 0 and DisableAGP 1.
The graphics card is now active with dxdiag showing AGP Support : Not Available.