Understanding the IRQ assignments table for my new ASUS A7V880 MB...

Discussion in 'Asus' started by G.L. Cross, Aug 4, 2004.

  1. G.L. Cross

    G.L. Cross Guest

    I've been building my own systems for about five years now but one thing has
    left me guessing as to exactly what information is being conveyed by the
    tables that appear
    in every MB manual I've seen regarding the expansion slots and which ones
    share IRQs.
    Here is the table from the MB manual and it seems to do nothing but confuse
    me so I am
    here hoping someone can explain exactly what this information means:

    INT D
    PCI slot 1 --- --- ---
    PCI slot 2
    red --- --- ---
    PCI slot 3 ---
    sed --- ---
    PCI slot 4 --- ---
    hared ---
    PCI slot 5
    red --- --- ---
    Gigabit LAN --- ---
    hared ---
    AGP slot (8x)
    --- --- ---

    OK here's the thing, every other time I've seen these tables they have had
    the columns filled in. So my questions are: How does INT A, INT B, INT C,
    and INT D relate to the IRQ asigned to a device in a particular slot. And
    do they mean by "used" (I hope this does not mean I can't install a card
    PCI slots 1 and 3). And finally, how do I determine which of these are
    "shared" slots (I sure hope the AGP isn't shared with slots 2 and 5). And

    final question: How do I determine if a certain device driver supports IRQ

    I want to configure this system with Windows-XP PRO and the following
    add-on cards:

    (1) ASUS V9180 Magic GeForce MX 440 8X AGP (for primary display)
    (2) Visiontek GeForce4 MX420 PCI (for second display)
    (3) ATI TV Wonder Value Edition PCI (TV-Tuner and Video Capture)
    (4) 3Com/US Robotics 56Kbps VOICE/FAX modem PCI (FAX & digital answering

    (5) ADI AD1888 SoundMAX 6-channel audio with S/PDIF-out interface (onboard)
    (6) Marvell 88E8001 Gigabit LAN adapter (onboard)

    You may send e-mail if you wish provided it is NOT SPAM. To decode my valid
    E-mail address, you will need to remove the <NOSPAM.> and the <666>. I had
    to get complicated as spammers are now doing the obvious removal of the word
    "NOSPAM" to compile their lists of e-mails...

    - G.L. Cross
    G.L. Cross, Aug 4, 2004
    1. Advertisements

  2. [garbled table deleted]
    I preferred to d/l the PDF manual... And please, check your line breaks.

    It appears PCI slots 1 and 3 do not share an INT line with anything
    else, so you should put interrupt sharing unfriendly cards into these.
    Slot 4 shares an INT line with the Gb LAN (I wouldn't put anything
    bandwidth intensive into that one), while 2 and 5 share one with the AGP
    You try out. Frequently it's not only a matter of the device itself, the
    drivers also play an important role - there have been cases where a card
    absolutely despises interrupt sharing in Windows but miraculously worked
    fine in Linux.
    Nvidia chips are usually not very keen on interrupt sharing.
    Put that one into one of the non-shared slots. Same goes for the 2nd
    graphics card, I suppose.
    This can probably live happily next to the Gb LAN.

    It would probably be easier to get a Yahoo! mail account, where you can
    set up disposable trash addresses. You may want to choose one containing

    Stephan Grossklass, Aug 4, 2004
    1. Advertisements

  3. G.L. Cross

    Paul Guest

    PCI slot 1 ‹ ‹ ‹ used
    PCI slot 2 shared ‹ ‹ ‹
    PCI slot 3 ‹ used ‹ ‹
    PCI slot 4 ‹ ‹ shared ‹
    PCI slot 5 shared ‹ ‹ ‹
    Gigabit LAN ‹ ‹ shared ‹
    AGP slot shared ‹ ‹ ‹
    I have a sneaking suspicion that this table only represents about
    1/4 of all the wiring information on the motherboard. One of the
    chipset chips has an interrupt controller on it, and the mislabelled
    four columns above represent the path the four wires take.

    Now, the thing is, a PCI card has four interrupt signals on it. A
    primary and three non-primary signals.

    From the PCI 2.2. spec:

    INTA# Interrupt A is used to request an interrupt.
    INTB# Interrupt B is used to request an interrupt and only
    has meaning on a multi-function device.
    << and so on for INTC# and INTD# >>

    What I think the Asus table is showing above, is how only the INTA#
    pin on each slot, is connected to the four wires streaming from the
    interrupt controller. So, in fact, the Asus table doesn't show how
    a multi-function device would be sharing interrupts.

    The normal practice in the PCI world is to "swizzle" the connections.
    This is a regular diagonal connection pattern, intended to equalize
    the interconnect. It is something like this. (Note: Example truncated
    to fit onto one line each.)

    S1 INTA# --> S2 INTB# --> S3 INTC# --> S4 INTD# --> S5 INTA# --> PIRQA#
    S1 INTB# --> S2 INTC# --> S3 INTD# --> S4 INTA# --> S5 INTB# --> PIRQB#
    S1 INTC# --> S2 INTD# --> S3 INTA# --> s4 INTB# --> S5 INTC# --> PIRQC#
    S1 INTD# --> S2 INTA# --> S3 INTB# --> S4 INTC# --> S5 INTD# --> PIRQD#

    The Asus table is basically only communicating what is happening
    to INTA# on each card (the primary interrupt). In my swizzle example
    above, slot1 and slot5 share a physical interrupt line, namely PIRQA#.
    Asus would mark slot1 and slot5 as "sharing" that signal. Since the
    PIRQB# signal only has Slot4's INTA# connected to it, Asus would use
    the word "used" when they should be using the word "unique" or
    "unshared" instead.

    To see the swizzle pattern for yourself, see pg.22 of this schematic,
    and notice how the signals change in an orderly fashion for the INTx#'s
    Translate "used" to "unshared" or "unique". Slot 1 or slot 3 is an
    excellent location for a Sound Card with a poorly written interrupt
    handler, on your A7V880.
    But the AGP _is_ sharing with slot 2 and slot 5. When physical signals
    are shared, the numeric IRQ assigned by the OS has to be the same for
    all the devices sharing that signal. Each handler executes sequentially
    until the PIRQ signal is found to be deasserted - at least that is
    my understanding of how sharing works.

    Example from Abxzone - P4C800 Deluxe (3C940 Lan on original deluxe)

    A B C D E F G H
    PCI slot 1 ‹ ‹ ‹ ‹ ‹ shared ‹ ‹
    PCI slot 2 ‹ ‹ ‹ ‹ ‹ ‹ shared ‹
    PCI slot 3 ‹ ‹ ‹ ‹ ‹ ‹ ‹ shared
    PCI slot 4 ‹ ‹ ‹ ‹ shared ‹ ‹ ‹
    PCI slot 5 ‹ ‹ ‹ ‹ ‹ shared ‹ ‹
    AGP Pro shared used ‹ ‹ ‹ ‹ ‹ ‹
    USB HC0 shared ‹ ‹ ‹ ‹ ‹ ‹ ‹
    USB HC1 ‹ ‹ ‹ used ‹ ‹ ‹ ‹
    USB HC2 ‹ ‹ used ‹ ‹ ‹ ‹ ‹
    USB HC3 shared ‹ ‹ ‹ ‹ ‹ ‹ ‹
    USB 2.0 ‹ ‹ ‹ ‹ ‹ ‹ ‹ shared
    LAN ‹ ‹ ‹ ‹ ‹ ‹ shared ‹
    SATA ‹ ‹ ‹ ‹ ‹ ‹ ‹ shared
    1394 ‹ ‹ ‹ ‹ shared ‹ ‹ ‹

    "Using the onboard LAN. Using USB. Disabled the firewire. Disabled
    on-board sound. Firewire card in PCI-3. Audigy1 in Slot #4. I have
    the Radeon on the AGP."

    I think his Audigy is actually in Slot 2. Firewire in Slot 3.

    Resulting Windows IRQ assignment - OCRed to table below:

    Resource Device status
    IRQ 0 System timer OK
    IRQ 1 Standard 101/102-Key or Microsoft Natural PS/2 Keyboard OK
    IRQ 3 Communications Port (COM2) OK
    IRQ 4 Communications Port (COMl) OK
    IRQ 6 Standard floppy disk controller OK
    IRQ 8 System CMOS/real time clock OK
    IRQ 9 Microsoft ACPI-Compliant System OK
    IRQ 10 Intel(R) 82801EB SMBus Controller - 24D3 OK
    IRQ 12 Microsoft PS/2 Mouse OK
    IRQ 13 Numeric data processor OK
    IRQ 14 Primary IDE Channel OK
    IRQ 15 Secondary IDE Channel OK
    IRQ 16 RADEON 9700 PRO OK
    IRQ 16 Standard Universal PCI to USB Host Controller OK
    IRQ 16 Standard Universal PCI to USB Host Controller OK
    IRQ 18 Standard Universal PCI to USB Host Controller OK
    IRQ 19 Standard Universal PCI to USB Host Controller OK
    IRQ 21 Promise Technology Inc. Ultra IDE Controller OK
    IRQ 22 3Com Gigabit LOM (3C940) OK
    IRQ 22 Creative SB Audigy OK
    IRQ 23 Standard Enhanced PCI to USB Host Controller OK
    IRQ 23 OHCI Compliant IEEE 1394 Host Controller OK
    IRQ 23 Texas Instruments OHCI Compliant IEEE 1394 Controller OK

    Things to note:

    1) The Promise controller on IRQ 21, suggest the Asus table is wrong
    and the Promise is actually on wire "F".
    2) IRQ 22 occurs twice, and must match, because 3C940 and Audigy are
    sharing via Slot 2.
    3) IRQ 23 shows two Firewire devices and a USB2. Notice again how the
    Asus table is wrong. Maybe the SATA and onboard Firewire should be
    switched in the Asus table ?
    4) Standard assignments are IRQ0-IRQ15. PCI devices start above those.
    IRQ16 to 19 seem to correspond to wires A thru D. IRQ20 to 23 seem
    to correspond to wires E thru H. The five PCI slots can only use
    IRQ20 to 23. Notice that the P4C800 Deluxe interrupt controller
    has eight wires, and yours has four wires. It doesn't change
    the fact that both boards use sharing.

    Moral of the story ? Load up the system with hardware first, then
    look in the Device Manager or use a utility like Sandra, to examine
    the IRQ assignments. Mark up the manual to reflect the real wiring.
    Reassign cards, according to your knowledge of cards known not to
    play nice. In my readings on the newsgroup so far, only a sound
    card really needs a private IRQ.
    Devices with high data thruput, or real time requirements, may have
    data overruns, data underruns, cause havoc via delays or freezes etc.
    If your system is misbehaving, start looking...

    No hardware manufacturer is going to admit they have a problem.
    Sharing is a requirement, after all, and they cannot admit to
    such a shortcoming.
    PCI slot 1 ‹ ‹ ‹ used
    PCI slot 2 shared ‹ ‹ ‹
    PCI slot 3 ‹ used ‹ ‹
    PCI slot 4 ‹ ‹ shared ‹
    PCI slot 5 shared ‹ ‹ ‹
    Gigabit LAN ‹ ‹ shared ‹
    AGP slot shared ‹ ‹ ‹

    You are using onboard sound, so no worry about finding a unique
    signal for a sound card. Modem card probably has a data pump
    (non-Winmodem), so will be interrupting when a FIFO of data bytes
    is ready. TV Tuner might be pumping a fair amount of data on the
    PCI bus, but doesn't have a good reason to be using its interrupt
    line. Here are my choices:

    AGP MX440 AGP (low power card - cooling not an issue)
    Slot1 MX420 PCI (higher priority than other PCI slots)
    Slot3 USR modem card (unique IRQ, no sharing, low latency)
    Slot4 ATI TV Wonder Tuner PCI

    I don't really know if the TV Wonder uses interrupts. Once slot1
    and slot3 are assigned, the other slots kinda stink. Sharing with
    the AGP card doesn't sound like fun. Sharing with the LAN would
    be bad practice as well, only because the interrupt rate on the
    LAN could be high. I placed the card in slot4, on the assumption
    that with the modem, you might not be using the LAN. If you are
    using the LAN, do a file transfer from another PC, with the
    TV Tuner running or not running, and see if there is a performance
    difference. Performance tuning will help you decide on a final

    If the MX440 runs hotter than I think it does, then try swapping
    the USR modem card and the MX420. If the USR card is smaller than
    the MX420, maybe it will leave more room for air movement. When
    I refer to cooling issue, I mean if there is a FX5900 or an ATI
    9800 in the AGP slot, you might not want a PCI card in slot 1.
    I don't know what I'd do if that was the case.

    Also, if you want a real laugh, download a few more Asus manuals.
    For example, the PC-DL is a desktop server board, and uses an 875
    Northbridge, like the P4C800 Deluxe example above. Look how the
    tech writer did the table:

    PCI slot 1 IRQ_F# IRQ_G# IRQ_H# IRQ_F#
    PCI slot 2 IRQ_G# IRQ_H# IRQ_E# IRQ_F#
    PCI slot 3 IRQ_G# IRQ_E# IRQ_F# IRQ_F#
    PCI slot 4 IRQ_E# IRQ_F# IRQ_G# IRQ_F#
    PCI slot 5 IRQ_F# IRQ_G# IRQ_H# IRQ_F#
    AGP Pro IRQ_A# IRQ_B# ‹ ‹
    Onboard USB1 IRQ_A# ‹ ‹ ‹
    Onboard USB2 IRQ_D# ‹ ‹ ‹
    Onboard USB3 IRQ_C# ‹ ‹ ‹
    Onboard USB4 IRQ_A# ‹ ‹ ‹
    Onboard USB2.0 IRQ_H# ‹ ‹ ‹
    Onboard LAN IRQ_F# ‹ ‹ ‹
    Onboard 20378R IRQ_H# ‹ ‹ ‹
    Onboard IDE IRQ_C#
    Onboard ICH5R IRQ_C# ‹ ‹ ‹
    Onboard 1394 IRQ_E# ‹ ‹ ‹
    Onboard AD1985 IRQ_B#

    Notice how in this example, the table attempts to show all the
    wiring. You have to rearrange the info from the first column, to
    make a table similar to the ones found in other Asus desktop
    motherboard manuals. Also note, how even the AC97 Codec is shown
    to have an interrupt, although other manuals never show this.
    The swizzle pattern for the PCI slots, is, in a word, nuts.

    Every manual I read, just creates more mysteries.

    Paul, Aug 4, 2004
  4. G.L. Cross

    G.L. Cross Guest

    It was fine when it went out but I noticed the post when it showed up
    and sent a cancel request for the first one. I guess you didn't notice the
    repost I put out 46 minutes later...
    Is there some reason why I should leave the "automatically wrap text at"
    setting to 76 characters? That's what happened to me the first time (those
    true-type fonts) and it garbled the table...
    Here's the thing that never got explained to me: this table implies that
    slot has four "INT lines" but I don't get the relationship between what this
    means (hardware design-wise) and how these INT A, INT B, INT C, etc.
    relate in any way to the sharing of IRQs. Plus the use of the word "used"
    I've never run across before...
    This fact I am already aware of. Also they sometimes get unstable (at least
    of the older ones) if you enable the "Read Around Write" BIOS setting of the
    VIA chipset. I do not know if this issue has been resolved with the newer
    chips or not. All that aside, Nvidia makes some damn good video chips (the
    GeForce MX 440 is capable of real-time full-screen antialiasing at a quality
    never seen before and a 200Hz refresh rate at 1024x768 resolution in 32-bit
    Yes, this is how I was planning to arrange them:
    AGP ===> ASUS video card
    PCI-1 ===> Visiontek video card
    PCI-2 ===> Two additional USB ports cabled to MB header (PCI-2 unused)
    PCI-3 ===> ATI TV-Tuner / video capture card
    PCI-4 ===> 56Kbps voice/fax modem
    PCI-5 ===> (unused)
    Funny! I did that once already. After returning from a two-week vacation, I
    over 800 SPAM messages, the vast majority of them porno...
    G.L. Cross, Aug 4, 2004
  5. G.L. Cross

    G.L. Cross Guest

    Thanks! I "think" I see what is going on now though I'll have to look
    over what you are saying some more.
    I am planning on using the onboard 6-channel sound. Seems to me that
    disabling it and then adding a different sound card - seems kind of
    since nowadays most onboard sound setups sound just fine to me (unless you
    are going to be a musician and need MIDI capability and lots of simultaneous
    "voices" to compose complex music... (just a thought).
    Interesting... I've always thought the IRQs stopped at #15. When did this
    change take place? I've always thought they needed to extend the number
    of available IRQs but I couldn't think of how it could be done with all the
    "legacy" stuff out there.
    Would it not degrade performance if one or more high-data rate devices
    (like the two video cards) shared an IRQ?
    I will be using the onboard LAN connected to a Microsoft
    802.11g/Wi-Fi Wireless-G router to share my cable modem
    connection with two "wired" systems (mine and my roommate's)
    and also allow me to wirelessly connect to the Internet from my
    Hp Pavilion 7000 series notebook. The FAX/VOICE modem
    is there primarily to send and receive FAX'es which comes in
    useful a lot. So with that in mind, I'd think about swapping the
    locations for the modem and the TV Tuner / Video Capture
    card (one of the reasons I'm putting together a two-display
    system: full screen TV on one monitor while I work at the other).
    Also the extra screen realestate can sure come in handy when
    you've got say a dozen open windows at once.
    [table omitted]
    I know what you mean. I was quite disappointed with the quality of
    the manual for this MB. It certainly was not up to ASUS or ABit's usual
    G.L. Cross, Aug 4, 2004
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.