Sound Blaster DIAGNOSE and Disabled MPU-401

Today I finally solved a nagging problem that always seemed like it had to have some sort of reasonable solution. Creative’s DIAGNOSE.EXE utility is quite useful when working with any Sound Blaster 16 derivatives (Sound Blaster 16, AWE32, Sound Blaster 32, AWE64). But there’s an annoying oddity related to the fact that many SB16-based cards have an MPUEN jumper which can disable the MPU-401 interface, typically accessible at port 330h. This jumper is very useful when a SB16 is combined with something like a Roland SCC-1 or a Turtle Beach Maui.

When the MPUEN jumper is set to disable the Sound Blaster’s MPU-401 interface, DIAGNOSE stops working:

DIAGNOSE MPU-401 Error This seems very unsatisfactory; the MPUEN jumper is well documented, so why would DIAGNOSE refuse working when the default setting is changed? After all, a user might not care for MPU-401 compatibility at all, or might have a system where ports 300h and 330h are already occupied by other hardware (SCSI HBAs, network cards) and needed to force the SB16’s MPU-401 to be disabled. Well, there is a solution…

And it’s very simple. All it takes is to run

DIAGNOSE /DMPU

and DIAGNOSE.EXE will skip MPU-401 detection entirely and continue on to the next test:

DIAGNOSE With /DMPUThe /DMPU switch appears to be undocumented and I could not find it mentioned anywhere. Yet it seems so obvious—the string ‘/dmpu’ appears in DIAGNOSE.EXE in plain text—that someone surely must have figured this out years ago? I’m not the first person to run into this problem, either.

The /DMPU switch was verified to exist at least in DIAGNOSE.EXE versions 4.01, 4.02, 4.04, and 4.06.

A remaining minor mystery is the fact that DIAGNOSE.EXE should under some conditions show a different MPU-401 test menu with added “Disable” option (it’s in the executable). This might possibly only apply to PnP Sound Blasters.

This entry was posted in Creative Labs, Sound, Sound Blaster, Undocumented. Bookmark the permalink.

3 Responses to Sound Blaster DIAGNOSE and Disabled MPU-401

  1. Laz M says:

    I remember this problem! I kind-of gave up on DIAGNOSE because of this very same error.

    This undocumented switch would have been VERY welcome knowledge.

  2. Matt Lacey says:

    This just made my day! Couldn’t get diagnose.exe to work and Windows 3.1 was also complaining about an invalid MIDI port (330 – default, and what is set via jumpers on my card). This fixed things up, but I’ve still got an issue… I updated the config files after running through diagnose.exe and everything was working, but I have to run it again after each boot if I want to get music in DOOM., any idea why? Makes little sense to me but I’ll keep poking around.

  3. Michal Necasek says:

    Depending on what sound card exactly you have and what system it’s plugged into, the card may need initialization which is performed by DIAGNOSE.EXE. Not so unusual actually.

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