Joseph Smith wrote:
FYI, here is what the ICH4 data sheet says about these 0x3d registers. Looks like the PIRQ is internally specific.
The ICH4 is a southbridge and contains many different PCI devices and legacy devices including the PIC and the PIRQ routing hardware to map the PIRQs to PIC int lines. As such it is not a good place to try and draw inferences from as it has a lot of capabilities not included in a normal PCI device.
Andrew