NeoG_ wrote on 2025-10-01, 04:14:

I like accessing the MPU-401 interface on my PicoGUS in win98, but the Microsoft and MusicQuest MPU-401 compatible drivers insist on taking IRQ9 which could be used for other devices. Is there a driver floating around that works with an MPU401 interface but doesn't take an IRQ?

IRQ9 is the default for MPU-401. However, this is also used by ACPI as SCI IRQ, resulting in a direct conflict against MPU-401 if Win98 is installed with ACPI enabled.

This is not a problem in environments that don't use ACPI, namely DOS. Some motherboard's BIOS had an option to send it to APIC territory but doing so kind of breaks ACPI for Win98 (the component in question will get a yellow exclamation mark complaining about not getting an IRQ).

As such, it may be a good idea to install or reconfigure Win98 to non-ACPI if using MPU-401. Use "/p i" argument to install Win98 without ACPI support, and you can refer to this to disable ACPI on an already installed Win98.

LSS10999 wrote on 2025-10-01, 10:19:

IRQ9 is the default for MPU-401. However, this is also used by ACPI as SCI IRQ, resulting in a direct conflict against MPU-401 if Win98 is installed with ACPI enabled.

That's what I originally thought, however the SS7 system in my signature has ACPI enabled and windows seems to be able to freely assign IRQ9. If I have the MPU-401 driver enabled it takes IRQ9 and doesn't report a conflict. If I remove the MPU-401 driver, IRQ9 gets assigned to "IRQ Holder for PCI Steering" and a random PCI device will get assigned to it (usually the SB Live). Since I may be adding more devices and I won't be using the MPU IRQ for anything I figured I would try and find an MPU driver that doesn't unnecessarily occupy the IRQ.

I have seen the effect of ACPI calls being blocked either from a card being installed in IRQ2 or ACPI being disabled in the BIOS, the system will lock up any time it needs to re-assign resources such as adding or removing devices in device manager and that doesn't seem to happen with IRQ9 assigned in windows itself.

Edit: Did 98 somehow get installed without ACPI support? There is no ACPI device in device manager, only Programmable Interrupt Controller on IRQ2, Plug and Play BIOS and Advanced Power Management. I guess that means the question is still valid.

LSS10999 wrote on 2025-10-01, 10:19:

As such, it may be a good idea to install or reconfigure Win98 to non-ACPI if using MPU-401. Use "/p i" argument to install Win98 without ACPI support, and you can refer to this to disable ACPI on an already installed Win98.

I think a better way of installing Windows 98 in APM mode (If you can't disable ACPI in the BIOS) is to use APMINST.INF.

Copy APMINST.INF to a location and then run setup with the full path to APMINST.INF (i.e. "setup c:\apminst.inf").

NeoG_ wrote on 2025-10-01, 11:13:

That's what I originally thought, however the SS7 system in my signature has ACPI enabled and windows seems to be able to freely assign IRQ9. If I have the MPU-401 driver enabled it takes IRQ9 and doesn't report a conflict. If I remove the MPU-401 driver, IRQ9 gets assigned to "IRQ Holder for PCI Steering" and a random PCI device will get assigned to it (usually the SB Live). Since I may be adding more devices and I won't be using the MPU IRQ for anything I figured I would try and find an MPU driver that doesn't unnecessarily occupy the IRQ.

I have seen the effect of ACPI calls being blocked either from a card being installed in IRQ2 or ACPI being disabled in the BIOS, the system will lock up any time it needs to re-assign resources such as adding or removing devices in device manager and that doesn't seem to happen with IRQ9 assigned in windows itself.

Edit: Did 98 somehow get installed without ACPI support? There is no ACPI device in device manager, only Programmable Interrupt Controller on IRQ2, Plug and Play BIOS and Advanced Power Management. I guess that means the question is still valid.

A correction, as I think MPU-401 originally used IRQ2, yet IRQ2 and IRQ9 are the same interrupt line IIRC. The PIC you mentioned, that's taking IRQ2, is probably the secondary one responsible for higher IRQ numbers. Other stuffs that would be on IRQ2, including MPU-401, would be assigned to IRQ9 instead.

On the other hand, by default Win98 Setup would try to detect ACPI before making the decision to actually enable ACPI support. If your board's ACPI is disabled, or is among the "bad BIOS", then ACPI support will not be enabled.

Does your board's BIOS come with options to reserve certain IRQ/DMA for Legacy ISA? If so, try reserving the IRQs that your cards are going to use. For older boards, this option does work, and other PCI devices will avoid using the reserved ones.

It is possible to remove the IRQ by editing the INF file for MPU401 compatibles (MIDI.INF).

Delete "IRQconfig" parameters and there isn't any IRQ wanted anymore.