SonicExplorer
Hi Guys,
 
I've been working away building a "new" DAW system (dual W2K and XP based with Intel motherboard) and was just about done, merely awaiting a Firewire card to be delivered, when suddenly I realized the entire effort may be headed for serious trouble.  It has been a long while since I built a DAW and assumed that motherboards still allowed for configuring IRQ's like most did "back in the day".  Well, looking in Device Manager I just realized a LOT of things are all lumped on the same IRQ.  I immediately went into the BIOS and ..... there is no way to adjust ANYTHING about the device IRQ's.  ARGH!!   What have I got myself into?  At the moment it looks like both PCI slots (where the firewire audio card and another audio card will go), the onboard video, onboard audio and one USB port are ALL ON THE SAME IRQ (16).   I'm thinking this cannot possibly be safe.
 
Should I throw in the towel on this system and start over with a higher end mother board that has at least one PCI slot not sharing any interrupt tie-line and has the IRQ controls necessary in the BIOS?  
 
Sonic

Have a look at APIC (Advanced Programmable Interrupt Controller). Properly supported in XP, supposedly.

In the BIOS, disable everything you don't need on the board.  That frees up IRQs.  The result: less sharing.

Did that already, there are free IRQ's yet the "genius" of Windows still decided to lump a bunch of things on IRQ 16.   
 
I went ahead and ordered a PCIe card, that should get around this issue since it should have it's own lane.  
 
I spent more now in PCI cards than the PC is worth. haha.  Between PCI, PCIe and potential on-board Firewire with some mobos, I should now have all the options covered going forward.   Let's just hope my trusty FF400 doesn't break down since it's the only reason I'll probably ever need a Firewire interface.... lol 

Argh!!!  I got the PCIe FIrewire card and Windows is STILL assigning the SAME IRQ to it !!!   
Everything is jammed on IRQ16, even though there are open IRQ's to be used.   Fireface 400, onboard audio, PCI busses, USB busses, onboard Video.... it's all jammed on IRQ16.    THIS CANNOT POSSIBLY BE SAFE for a DAW is what I maintain.   The one thing I did notice however is that all these other entities are on "PCI Bus 0" whereas the PCIe Firewire card is listed as being on "Bus 2".   So that's probably a good sign.  But still, having assigned the same IRQ....WHY!?
 
Does anybody have any ideas at all about how to force Windows to use one of the open IRQ's, or to set it manually??   I'm already using the only PCIe slot, so moving the card isn't an option.
 
This is the LAST issue remaining, I would hate for it to cause me to scrap this whole effort and move to another motherboard simply to be able to control the IRQ settings.  I just never anticipated Windows would be so brain-dead.
 
    Sonic

Is this, so far, still a theoretical problem? Or are you experiencing lots of dropouts and other issues?

On shared IRQ's, there is a priority order.  If the device you want is the primary device it will have priority use over the other(s).  
 
Its been a while since I've had and used XP, but I recall being able to manually assign open IRQ's to devices.  I remember doing this in the Device Manager for the specific device.  
 

https://support.microsoft.com/en-us/help/182604/description-of-pci-bus-irq-steering

I get the feel you are trying to apply DOS mentality to an environment where it is not applicable. You are trying to control something better left alone.

No, this is a very real concern.  And just because something might not be obvious up front doesn't mean it isn't a trainwreck waiting to happen in the midst of a session.  There is a misunderstanding in thinking the whole IRQ issue has been solved by modern BIOS and Windows enhancements.  Granted it is not quite the same type of concern as back in the day prior to W2K with IRQ conflicts, but it is still a very real concern.  There are two levels of things going on, one is the actual interrupt layout at the physical board design layer, the other is the IRQ assignment.  Even when using APIC, if things are lumped onto a single IRQ it seems that is still asking for trouble.  Every device still has to service an inquiry to see who is supposed to service the interrupt.  The more devices on the same IRQ, the more queries, and the higher likelihood if anybody does not behave properly & expeditiously there can be negative impacts to audio streams.
 
If somebody can explain how this is NOT a concern, please do so, I'm interested to learn why you feel what I've stated isn't valid.
 
Here is the Intel manual WRT the controller involved: https://www.intel.com/content/www/us/en/io/i-o-controller-hub-7-datasheet.html
For more detail look at sections on pages 43, 62 and 140.   I'm trying to decipher all this still so any help is appreciated.   From what I can see so far, it does seem in APIC mode most single-trigger entities will end up on IntA and IRQ16.   I can't believe there isn't some way to have at least ONE isolated card/bus.  Every board used to have this ability back in the day.  I'm also perplexed why open legacy IRQ's below 16 seem like they can't be used.   Anyway, this is a bit over my head so maybe some of the techy guru's on the forum can figure this out... 
 
Sonic

My PCIe Firewire card is assigned IRQ16.  It works perfect and I have no dropouts with my MOTU896Mk3 Hybrid recording interface connected to it.
There are other devices, such as "High Definition Audio Bus" also assigned to IRQ16
 
 

fireberd
My PCIe Firewire card is assigned IRQ16.  It works perfect and I have no dropouts with my MOTU896Mk3 Hybrid recording interface connected to it.
There are other devices, such as "High Definition Audio Bus" also assigned to IRQ16

 
Thanks for the reply.  What exactly is on your IRQ16..... USB, Video, Audio, etc.... Anything actually being used on IRQ16 besides the Firewire card?