That "IRQ sharing" thing is usually deeper than that, the manual only really gives you info on IRQ_A line. The AGP has two lines connected to it (A and B) and IIRC the PCI has 4. And there's only so many unique IRQs the chipset can handle. So pretty much everything is connected and it's up to the OS to sort it out. Well, OS and cards since the card could only be using IRQ_A and thus forcing the issue, though sensible designs would at least connect 2 for flexibility.

And speaking of OS, that's usually the main problem. With old, rather dumb OS (like Win9x) and slow single core CPU you really want to avoid any IRQ sharing. With Linux and Win2k or above it's not that critical, esp. if the CPU is at least a fast P2 or P3. But in any case you wan't to avoid sharing IRQ between devices that generate heavy load, or are very random, and devices that are somewhat time-critical. So in other words do your best to avoid sharing IRQ between USB and sound cards, possibly also graphics card (that only applies to heavy use of 3D). If possible also do not put NIC and sound on the same IRQ, especially if you have a lot of broadcast/multicast traffic in your LAN.

NIC+VGA should be okay. Depending on how good the USB implementation is, and how fast the CPU is, you might get away with USB sharing IRQ with VGA even in 3D games. USB+NIC is problaby fine, you will not have the LAN that saturated that it would affect your keyboard/mouse response, and dropped packets now and then are normal. Sound is the most critical to get right because, for latency reasons, the buffers are small and you need that realtime-like IRQ response. Everything else... just put it in and see what it does. If there are no problems then there is no point in messing with it.

I prefer to minimize the number of PCI cards. I never use PCI disk controllers anymore. They are a common source of instability and disk corruption, especially with VXD drivers and Win9x PCI support. PIIX4E UDMA 33 is fine and I think it's part of the experience anyway. I just run a mid 2000s 80GB HDD that is super fast and huge compared to a '90s drive.

I think I usually do NIC in PCI2 and sound in PCI3. PCI 5 and 6 are best used for a Voodoo 1/2 because they don't use DMA.

Deunan wrote on 2024-12-13, 09:24:

That "IRQ sharing" thing is usually deeper than that, the manual only really gives you info on IRQ_A line. The AGP has two lines connected to it (A and B) and IIRC the PCI has 4. And there's only so many unique IRQs the chipset can handle. So pretty much everything is connected and it's up to the OS to sort it out. Well, OS and cards since the card could only be using IRQ_A and thus forcing the issue, though sensible designs would at least connect 2 for flexibility.

PCI cards pretty much always use INTA# on the slot by default (which is what tools also report), and this is connected differently per slot to INTA#-INTD# on the chipset side, to make the best possible use of resources. using more than one INT line is really just meant for cards that combine several functions, as maybe some capture cards.

the exception IIRC are a few very early PCI cards that would allow to select INTA#-INTD# per jumper, but it's hard to see the purpose of that. you could argue it could potentially save a slot swap, but some board makers tended to not list the INT line map anyway, like MSI (no pun intended with message signaled interrupts), so you'd be stuck with trial-and-error in any case. being able to select the interrupt line just overcomplicates things, which is probably why that idea was done away with quickly.

as for IRQ sharing, i think sharing the USB and NIC is the best option, haven't noticed any trouble with that at least. even that can be avoided by reverting to a PS/2 keyboard+mouse, which have their own dedicated IRQs, though the latter will feel like a big downgrade in smoothness compared to USB. by the way, interestingly, comparing the manuals for the asus P4T and CUSL2-C, the former gives the usual four lines with shared AGP slot, while the latter gives eight - a bit strange given that both use the ICH2 that added the extra four interrupt lines, but maybe the latter refers to an APIC setup (i.e. running win2k).

oh2ftu wrote on 2024-12-13, 08:15:

Do some cards handle irq-sharing better than others? by type and model?

As for all I know, PCI IRQ sharing is mostly a driver problem.

Some Bios allow one to set which "legacy" irq is coupled with which PCI IRQ (ABCD) and you could set all those pci irqs to the same "legacy" irq and depending on which driver / windows version you have, the combination of cards can work or not.

Imo delete the USB card and just use onboard