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IRQs: When will 32 IRQs come out?!

  • Motherboards
Last response: in Motherboards
a b V Motherboard
December 13, 2000 8:14:32 PM


After seeing all the bloody mess with ACPI, PNP, and all that junk, when will we see a 20 year old problem fixed? Would it not be simpler to just add in an additional 16 IRQs so that we will never have to see IRQ conflicts anymore?

Everyone wants to see things working without a problem. How can we reinvent the wheel where everyone can win by adding the extra IRQs and haveing Chipset makers create the multichannels we need for 10 PCI Cards/Onboard Devices...

Is it just me or are others feeling the same thing?

New CPUs, Buses, devices, ACPI/PNP. All I want is to finally HAVE 32 IRQs to stop IRQ conflicts!

More about : irqs irqs

December 16, 2000 1:01:20 PM

why do you need them? there will be 31 IRQs if at they come. ever thought why there are 15 instead of 16?

December 16, 2000 4:51:32 PM

it would be 0-31 so 32 total no?
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a b V Motherboard
December 16, 2000 4:56:22 PM

There are 16 IRQ's, you should start counting with 0 (zero)!
December 16, 2000 7:13:32 PM

yes there are 16 IRQs, but IRQ2 is asigned to Programmable Interup Controller. An IRQ for the IRQ controller itself?
Its for historical reasons, the original PC (8088 based) used two interrupt controller chips, the 8259s each having 8 IRQs. One was named primary and the other secondary. IRQ0 of the secondary goes to IRQ2 of the primary, thus cascading two controlers to form a single interrupt controller having 15 IRQ lines. That is why there are only 15 and not 16 usable/available IRQ lines, most of which are already assigned.

a b V Motherboard
December 16, 2000 8:13:04 PM

Well, there is such a thing as IRQ0 But never shown. IRQs start at 0-15 and with the 32 IRQs it would be 0-31.

New CPUs, Buses, devices, ACPI/PNP. All I want is to finally HAVE 32 IRQs to stop IRQ conflicts!
December 16, 2000 8:29:00 PM

you wont get 32 IRQs. the cascaded IRQ is not supposed to be counted. and if the interrupt controller ever supports more than 16 IRQs it would naturally do 16 of them giving you 31 IRQs, 0 to 31 but 2. hope they dont cascade another 16 interrupts controller with the existing one. then we will have only 30! but thats much better than playing and sharing IRQs

December 16, 2000 8:36:04 PM

IRQ0 is shown as timer interrupt since the 8088 days. its legacy configuration and we cannot change that. IRQ1 for keyboard, 2 - the cascaded one (that brings another 8), 3 & 4 for serial ports, 5 free (now used by the sound card) 6 for the floppy disk controller and 7 for the printer. later on oter devices such as hard disks came around took charge of IRQs 14 and 15. newer devices took other IRQs, and still remaining IRQs are left to us to juggle with!

December 17, 2000 1:46:07 AM

Isn't PNP or the PCI bridge suppose to take care of this? It's not suppose to matter if IRQ's are share right? It seems to for the most part but I do see bad results from time to time.

<b> Fragg at will!!! </b>
December 17, 2000 5:53:23 AM

bad result are due to scarcity of IRQs, and that is why they are "shared". but how are they shared????
well, an IRQ is a signal that propogates thru the interrupt controller to the cpu by changing the logic level of the line, that is going from low level to high level. This is again classified into two types, edge triggered and level triggered, and making two devices use each of these methods allows them to share the IRQ. if the line stays high for a stipulated period, its given in favor of one device whereas if it just pulsed, then the other device is favored.

the pci bridge and the PnP thing just conveys the info about the device regarding what IRQ and I/O space it should use and the OS (in most cases windows, linux is also a PnP OS) should there be any conflict, the os attempts to assign ather IRQ to that device or shares that IRQ among devices. if the device refuses to obey this, then there is a IRQ conflict.

this can be solved by trial and error method, putting in one card at a time, and changing the sequence if any card locks up.

a b V Motherboard
December 17, 2000 4:33:41 PM

NEVER! (Hargh Hargh)

Seriously, with all USB devices on one IRQ, and PCI Steering or ACPI, who needs more than one or two IRQ's free? Admittedly, I like to keep my graphics card on a separate IRQ, but, what else do you need?

Here's an example of all the IRQ's needed on a modern system:

00 System Time
01 Free
02 Interrupt Controller
03 Free
04 USB Controller
- Mouse
- Keyboard
- Printer
- Scanner
- WebCam
- ...
05 Free
06 Free
07 Free
08 Free
09 Cascaded
10 Free
11 Free
12 Free
13 Numeric Processor
14 GFX Card
15 PCI Steering / ACPI IRQ
- Sound
- Network
- Hard Drive
- Floppy Drive
- TV Card
- ...
a b V Motherboard
December 18, 2000 2:58:27 AM

ok then enjoy trying to debug your problems, poppings with your sblive, etc.... Me personally, I would rather have separate IRQ Channels for each device. Atleast I will be 100% sure my system will not fault cause of an IRQ/Bus Master/ACPI problem.

New CPUs, Buses, devices, ACPI/PNP. All I want is to finally HAVE 32 IRQs to stop IRQ conflicts!
a b V Motherboard
December 18, 2000 3:00:13 AM

forgot to mention, if you share IRQs, you are also reducing your bus bandwidth on that IRQ. So if you put your SCSI and IDE controllers on the same IRQ, don't expect fast transfer rate between the 2 devices...

New CPUs, Buses, devices, ACPI/PNP. All I want is to finally HAVE 32 IRQs to stop IRQ conflicts!
a b V Motherboard
December 18, 2000 3:09:15 AM

Well yes they are suppose to but I would personally feel much safer to have the extra 16 IRQs (or atleast 8 more IRQs) to put devices on it.

We have seen everything else improve (PCI, PCI-66, AGP, Chipsets, CPUs..) why finally not improve the low level areas that would atleast not be dependant with Card/Driver conflicts, poor performance with IRQ sharing, and just constant freezing cause of the shared devices.

New CPUs, Buses, devices, ACPI/PNP. All I want is to finally HAVE 32 IRQs to stop IRQ conflicts!
December 18, 2000 6:20:02 PM

Who dares to say we dont need more than 15 IRQs.:-)
Look what a mess Windows makes from what is availlable!
Everything is working without conflict but..........

00 - System timer
01 - Keyboard
02 - Programmable interrupt controller
03 - ??????
04 - Com 1
05 – Intel 82371AB/EB universal host controller for PCI to USB
05 – IRQ holder for PCI steering
06 – Standard diskette station controller
07 – ECP printer port controller
08 – System CMOS/Real-time clock
09 – Soundblaster 16 or AWE 32 or compatible
10 – Conexant PCI modem emulator
10 - IRQ holder for PCI steering
11 – Diamond Viper 550
11 - IRQ holder for PCI steering
12 – Adaptec AHA-294X/AIC-78XX PCI SCSI controller
12 - IRQ holder for PCI steering
13 – numeric processor
14 – Intel 82371AB/EB PCI Busmaster IDE-controller
14 – Primary IDE controller (double fifo)
15 - Intel 82371AB/EB PCI Busmaster IDE-controller
15 – Secondary IDE controller (double fifo)
a b V Motherboard
December 19, 2000 3:33:09 AM

Although I would love to see 32 IRQ's available. I find much greater frustration in Chipsets that assign IRQ's to be shared between slots. I am completly frustrated by the fact that my VIA-Based Motherboard only allows me to effectively use 3 cards, even though i have six slots. I have no shortage of IRQ's, but the Motherboards forces the slots to share resources. As a result, i cannot use my dvd decoder card or my network card if i want to have ATA support and sound.
December 19, 2000 1:10:22 PM

VIA sucks...

-<font color=red><b>R.K.</b></font color=red>
December 19, 2000 5:00:53 PM

tried switching slots? or putting in one card at a time? i bet you will get all your cards functional.

December 19, 2000 5:13:55 PM

have you ever tried such a combination? it looks a nightmare, too fantastic!
i like watching sci-fi's, but whats this?

most of the IRQs listed free by you are already hard-wired since 1980, and practically thre are only about 5 IRQs free (namely 5, 8, 9, 10, and 12)
By using USB devices we can free kbd/com1/com2/lpt1 that is 1, 2, 3 and 7. what next? give 5 to the sound card, and 7 to the USB controller. we still have only 4 IRQs although most of our "peripherals" - note this word, are hooked to the USB. this means to add a modem you need to get a USB modem, a modem card will eat one IRQ!

Unfortunately internal devices (floppy drive, hard disk, the timer, co-processor etc) must be run on IRQs.

and after you hook everything on the USB somebody will complain about not having enough USB channels to use or not enough bandwidth for all devices :-)

what then? start using the IRQs you are keeping idle :-) :-)