Unable to use BAR sizes above 2 GB despite above 4G decoding being active on Z77 Maximus V Formula

[pntsrgd]

System

• Motherboard: ASUS Z77 Maximus V Formula
• CPU: Intel Core i7-3770K
• BIOS Version: 1903
• GPU: RX 6600 XT, RTX 5080
• CSM is turned off.
• 4G decoding is enabled.
• [Y] I have read Common issues (and fixes)

Above 4G decoding appears to be active. I see PCI Express Root Complex listed under "large memory" in the Windows device manager. No DSDT modding appeared to be necessary.

When I set BAR sizes <2 GB, it works reliably. I have had some instances of a 2 GB BAR failing. BAR >4 GB never posts successfully.

BIOS is patched. When attempting to boot with >2 GB, I get POST code D4 - "PCI resource allocation error. Out of Resources." This would seem to imply to me that something about the patching is still failing to allow the GPU to allocate above 4 GB.

Any ideas on what I should be looking for to resolve this? I assume this can be made to work, given that the Maximus V Gene is apparently working up to at least 8 GB.

[xCuri0]

are you sure you did uefipatch ?

[pntsrgd]

are you sure you did uefipatch ?

I did. I even considered that maybe I forgot to and pushed the image back through.

M5F.zip

The image is attached here. I just tried to run it through UEFIPatch again - received the message "No patches can be applied to input file."

[xCuri0]

if you have 32gb ram installed then 16gb bar won't work btw, it's because of a hardware limitation combined with the PCI allocation order on these boards not being ideal.

[pntsrgd]

if you have 32gb ram installed then 16gb bar won't work btw, it's because of a hardware limitation combined with the PCI allocation order on these boards not being ideal.

I do have 32 GB RAM installed, but I can't even get 4 or 8 GB BAR to work. I just can't get the GPU into large memory.

[xCuri0]

32GB causes weird stuff like this, 8GB should work though but maybe u have too many PCIe devices or something. Try disabling the integrated GPU if it's not already