IRQ Sharing: Interesting Lesson Learnt

[Qwerty]

I recently upgraded my PC and used the old bits and pieces to build a DAW for my guitarist and partner in crime. P4 1.8GHz, 1G Ram running Win2K. I just did a normal ACPI install and let Win2K work out the IRQ assignments.

Installed everything and it was smoking along, giving me a WDM latency of 5.2msec.

If I looked at Device Manager and went View - Resources By Type, I could see the sound card was sharing IRQ #19 with one of the USB host controllers and something else that I have forgotten. I went "Huh", and didn't care about it because everything was working.

Anyway, last weekend I stuck a CD burner into the box and while I had the case open, I shuffled the PCI cards to see whether I could get the sound card onto its own IRQ. When I brought it back up, the sound card was now sitting by itself on IRQ #14 (or a lower 'teen, anyway).

I went back into Sonar and re-profiled the sound card. Latency is now down to 3.5msec.

I was surprised that it made that much of a difference. Even in playback and moving around in a complex track, Sonar now seems a lot more responsive. So yeah, IRQ sharing looks like it works, but it sure as hell ain't the desired scenario!

Q.

 

[guttadaj]

Hey, Qwerty.

Thanks for sharing! I have the same thing going on here. I installed my new Audiophile 2496 a while back, and it's working now, but I did notice it's sharing an IRQ with one of my USB Host Controllers too. I didn't think much of it, but now I think I'll get back under the hood and do some moving of stuff to see if I can fix that. (Also, my Santa Cruz is no longer working I think due to an IRQ conflict, so I'll try to fix that in the process.) Do you know - does each PCI slot have a specific IRQ that any card you try to install will use, or do the IRQ's get assigned sort-of randomly (or at least differently)? My PCI slots are all full, so I'm wondering if uninstalling/reinstalling and possibly moving cards around would yield different IRQ assignments. Anybody know of a way to manually assign the IRQs? Sheeesh - you'd think that would be something that should be easy enough to do...

Well, anyway, thanks for sharing the experience.


Jeff

 

[Qwerty]

Hi Jeff,

My understanding is that the modern PCI bus uses IRQ bridging to provide a big enough number of shareable IRQ's. The five slots on my motherboard, and most of 'em, will have different IRQ's assigned to them depending upon what slots are used and what's plugged in where. Your motherboard manual should have a diagram showing these assignments... Or just start card shuffling and see where ya get

You can manually assign IRQ's but to do this requires that the OS was installed as a STANDARD PC as opposed to an ACPI UNIPROCESSOR. Unfortunately, the only way I know to change between the two is via a complete system re-install.

Ciao,

Q.

 

[guttadaj]

Thanks for the info, Qwerty. I guess "Plug and Play" is quite an accurate term then. After you Plug it in and see that it didn't work, it's time to Play a little game of "musical PCI cards". I'll give that a shot and see what happens.

 

[Secret Clubhous]

IRQ changing

Yeah, I've had problems w/my computer crashing in CW. I emailed CW support & this is what they said:

It sounds like an IRQ conflict. Make sure that your USB Port, sound
and video cards are not sharing IRQ numbers with any other device. PCI
steering should be OK. If they are you can should locate a number that
doesn't appear in the list and change it to that number. If you need
help doing this, then you should contact your computer manufacturer
for instructions on changing the IRQ.

1) Go to Start > Settings > Control Panel > System > Hardware > Device
Manager

2) Choose View > Resources by Type

3) You'll a list of devices and their respective IRQs.

4) Alternatively you can run MSINFO32 and export the file as .nfo (to
view
on other XP systems) or as a .txt file.

Also ACPI can keep you from changing IRQs and may cause other problems
with Cakewalk. Here are the steps to disable it:

1. Boot from the Windows Install Disks (or directly from Windows CD)

2. Press F5 at the point where the "Press F6" message appears and
choose 'Standard PC' when prompted.

3. To set up Windows XP now press 'Enter'.

4. Read and agree to the license agreement and press F8.

5. Continue through the install sequence. When the installer detects
your existing version of Windows, it will ask if you want to repair
the existing install or overwrite it. Press "R" to choose repair.

6. Continue through the install sequence. Keep driver disks handy, as
you may be prompted for some drivers.

When the install finishes, Windows will be installed in Standard PC
mode, but all existing programs and ​

settings will remain intact.


Seems all my USB ports share #21. My "sound card" is the Tascam US-122 (USB) & the only other USB device I have is a printer. The computer has a cheapo Realtek soundcard that is #22 but I don't use it.

anyway I'm pretty confused here. I have emailed CW support for clarification but I think I need some support to be able to understand what they are talking about!

My "computer manufacturer" is a local shop that built my rig but they say they don't support the OS cuz they consider it software, not hardware.

1. How do you change IRQ #'s?
2. How do you "boot from the install disk"? I put the disk in but it boots up to the regular opening XP screen. There is no message about pressing an F key that I could see. While it was booting, I pressed F5 anyway but it did not present any choices--only XP.
3. Is it really necessary to re-install the whole OS or is there a way to just do a repair on the existing install?
4. What does "standard PC" mode mean?

Can anybody explain in simple language for a non-techie what I need to do & the best way to do it?

 

[tombuur]

Yeah, let's get this straight. I too am somewhat confused. My M-Audio card shares an IRQ with the ACPI-controller. Don't know if it matters. I also have very few extra IRQ's to choose between, if any.

One solution when running out of IRQ's is disabling unused devices. For instance there are com1 and com2 ports. Most of us don't use these after USB came along. If your printer uses USB you can disable LPT too. I guess in most cases this is done by holding down <del> when powering up the computer and then finding where in the menus to disable stuff.

 

[lykwydchykyn]

1. How do you change IRQ #'s?
2. How do you "boot from the install disk"? I put the disk in but it boots up to the regular opening XP screen. There is no message about pressing an F key that I could see. While it was booting, I pressed F5 anyway but it did not present any choices--only XP.
3. Is it really necessary to re-install the whole OS or is there a way to just do a repair on the existing install?
4. What does "standard PC" mode mean?

Can anybody explain in simple language for a non-techie what I need to do & the best way to do it?

1. To change IRQ's in windows XP, you need to go to device manager: right-click "my computer", select "manage", select "device manager". On the right you'll see all the hardware on your pc, organized by type. Double-click on a piece of hardware you want to change to bring up its properties. Go to the "resources" tab. Uncheck "use automatic settings". Bah-bam there you go.
2. You need to make sure your BIOS is set to boot to CD. How exactly to do this depends on the make of your MB. Some newer BIOSes feature a "boot menu" function, where you hit a key like f8 or f12 while it's booting and that gives you a menu of which device you want to boot from. Also, when booting to the windows install CD, it will ask you to "press any key to boot from CD". If you don't hit a key, it will default back to your hard drive.
3. not sure, but since a repair won't screw anything up, it's worth trying. In fact, it's liable to fix a few things. You may need to get your service packs again, not sure about that.
4. I won't try to explain that. You probably don't want to know anyway.

One more thing I would encourage people to do who want to streamline their PC: go into your BIOS/CMOS setup and disable built-in devices that you don't use. If you don't use the serial port, disabling it frees up an irq. Same with the parallel, game/MIDI (if you have an external MIDI interface, you don't need this), onboard sound, LAN or modem (whichever you aren't using for your internet), etc. Just don't disable anything if you don't know what it is.

 

[Secret Clubhous]

OK, I tried to implement your advice. All the USB ports/host controller share IRQ #21. No indication which device is plugged in where. The US122 or the printer was not listed specifically so there was nothing to change. Under the resources tab, "use automatic settings" was greyed-out for all USB's so I couldn't uncheck any of them. The default cheapo sound card uses IRQ 22 but I don't use it. I got rid of a USB cordless mouse & am now back to PS2 for that.

I've tried pressing any & every key while booting but it still defaults to the hard drive. Not sure exactly what a BIOS is but I have been advised not to mess with it unless you know what you're doing.

My MB is labeled "MSI KM2M Combo MS6738 (v1.X) ATX, G52-M6738XI-L03 designed for AMD Athlon XP/Athlon/Duron processor, VIA KM266 Chipset Based." (computer has AMD 2400).

This is getting more & more complicated. Wouldn't it be easier & just as effective to just unplug the printer from the USB port, as a start or a workaround?

 

[Qwerty]

Shuffle your cards.

Q.

 

[guttadaj]

Yeah, I just shuffled my cards this weekend, and now my Audiophile 2496 card is the happy owner of its own IRQ number! Happy days... I ended up yanking my Santa Cruz since I needed the extra PCI slot for a USB 2.0 PCI card, plus I only wanted it in there for MIDI sounds (will just use softsynths) and so I could listen to stuff through the computer on headphones (will just do without or hook up the ole mixer for that).

-Jeff

 

[Qwerty]

Excellent. I'm not insane.

Q.