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Understanding IRQ assignments table for A7V880 MB... (repost)
I've been building my own systems for about five years now
but one thing has always 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 A INT B INT C INT D ------------------------------------------------------ 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 --- --- --- OK here's the thing, every other time I've seen these tables they have had all the columns filled in. So my questions a How does INT A, INT B, INT C, and INT D relate to the IRQ assigned to a device in a particular slot. And what do they mean by "used" (I hope this does not mean I can't install a card into PCI slots 1 and 3). And finally, how do I determine which of these are *really* "shared" slots (I sure hope the AGP isn't shared with slots 2 and 5). And one final question: How do I determine if a device driver supports IRQ sharing? 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 (primary display) (2) Visiontek GeForce4 MX420 PCI (second display) (3) ATI TV Wonder Value Edition PCI (TV-Tuner and Video Capture) (4) 3Com/US Robotics 56Kbps VOICE/FAX modem PCI (5) ADI AD1888 SoundMAX 6-channel audio with S/PDIF 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 |
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G.L. Cross wrote:
I've been building my own systems for about five years now but one thing has always 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 A INT B INT C INT D ------------------------------------------------------ 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 --- --- --- OK here's the thing, every other time I've seen these tables they have had all the columns filled in. So my questions a How does INT A, INT B, INT C, and INT D relate to the IRQ assigned to a device in a particular slot. The IRQ is not assigned to the devices in any slots (unless you're talking ISA slots). There's just a mapping scheme programmed into the chipset between INTs and IRQs or, more precisely, between the chipset's INT- inputs and it's IRQ output. In other words, the chipset has say 4 or 5 inputs on which all possible INT-type interrupt originators must be connected. Then the chipset can be programmed to generate say IRQ10 when input 1 is triggered, IRQ11 when input 2 is triggered, IRQ 9 when input 3 is triggered etc. Since there are more than 20 INT-type possible interrupt origins on the motherboard ( 4 x 5 PCI slots, 2 x 1 AGP slot, plus whatever other onboard PCI devices) which all must connect through those 4-5 inputs, some sharing is bound to happen. This is *hardwired* sharing. The best guess from above table is: Let's call the chipset's INT-type inputs input1 - input4 Since the important INT line on any given PCI slots is INTA (as all single function PCI devices must use INTA by definition) the above table actually only shows how the INTA line on the slots is connected. So we have: The INTA line on PCI slot 1 connects to input4, which is therefore *used* but nothing else connects to that input so it is not *shared* The INTA line on PCI slot 2 connects to input 1, onto which also connect the INTA lines of PCI slot 5 and the AGP slot, and therefore is *shared* This automatically gives explanation for PCI slot 2 and the AGP slot The INTA line on PCI slot 3 connects to input 2, which is therefore *used* but not share (same case as PCI slot 1) The INTA line of PCI slot 4 connects to input3. The onboard PCI gigabit line (which uses a single INT line too) has its line also connected to input3. Therefore that input is *shared* And what do they mean by "used" (I hope this does not mean I can't install a card into PCI slots 1 and 3). Get serious now Of course you can install cards. The worst restriction I can recall on PCI slots on 'modern' systems had to do with slave-only PCI slots which wouldn't take busmaster cards and that was like in the 1999 days. There may be a million reasons a motherboard can't take a particular card on a particular slot but nothing of this kind. And finally, how do I determine which of these are *really* "shared" slots (I sure hope the AGP isn't shared with slots 2 and 5). Easy answer: there's no such thing as shared slots except maybe PCI/ISA or PCI/ACR etc slots which line up to the same expansion slot :P Complicated answer: After we establish that by 'shared slots' we actually imply slots which lead to shared IRQs, the answer is that all slots are "shared"! It really depends on how many INTs a particular card will use. And the diagram presented in the manual doesn't mention how INTB INTC and INTD are routed (they're usually circularly shifted around though). If we restrict ourselves to PCI cards that only make use of INTA, then the table can be used to draw conclusions: slots marked *used* are not shared and have have an independent IRQ assigned to the device they accomodate. slots marked *shared* are inevitable shared with the slots/devices which also are marked *shared* on the same column. In short: PCI slot 1 can have an independent IRQ PCI slot 3 can have an independent IRQ PCI slots 2, 5 and the AGP slot will always have the same IRQ PCI slot 4 and the onboard LAN will always have the same IRQ However I restate that this only applies when INTA only cards are used (as IRQs refer to the actual devices on the cards that reside in the slots, rather than to the slots themselves). Also, this mapping scheme is rather irrelevant with ACPI which will install everything on a single IRQ anyway, or with modern APIC-enabled motherboards which can then spread the PCI devices over more than 4 IRQs. So either way IRQ sharing shouldn't be much of a concern. The table has value when running in classic PIC mode with only IRQs 0-15 present. And one final question: How do I determine if a device driver supports IRQ sharing? Ask the driver coder or just see for yourself Usually this is a non-issue these days though. Even the SB live!'s drivers support IRQ sharing and SMP properly now! 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 (primary display) (2) Visiontek GeForce4 MX420 PCI (second display) (3) ATI TV Wonder Value Edition PCI (TV-Tuner and Video Capture) (4) 3Com/US Robotics 56Kbps VOICE/FAX modem PCI (5) ADI AD1888 SoundMAX 6-channel audio with S/PDIF interface (onboard) (6) Marvell 88E8001 Gigabit LAN adapter (onboard) Here's a sample config: AGP = Asus PCI 1 = ati tv PCI 2 = visiontek PCI 3 = modem Regards Nikos ----- 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 |
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"Nikolaos Tampakis" wrote in message
news:1091979275.795654@athnrd02... If we restrict ourselves to PCI cards that only make use of INTA, then the table can be used to draw conclusions: slots marked *used* are not shared and have have an independent IRQ assigned to the device they accomodate. slots marked *shared* are inevitable shared with the slots/devices which also are marked *shared* on the same column. In short: PCI slot 1 can have an independent IRQ PCI slot 3 can have an independent IRQ PCI slots 2, 5 and the AGP slot will always have the same IRQ PCI slot 4 and the onboard LAN will always have the same IRQ However I restate that this only applies when INTA only cards are used (as IRQs refer to the actual devices on the cards that reside in the slots, rather than to the slots themselves). Also, this mapping scheme is rather irrelevant with ACPI which will install everything on a single IRQ anyway, or with modern APIC-enabled motherboards which can then spread the PCI devices over more than 4 IRQs. So either way IRQ sharing shouldn't be much of a concern. The table has value when running in classic PIC mode with only IRQs 0-15 present. [ stuff removed ] 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 (primary display) (2) Visiontek GeForce4 MX420 PCI (second display) (3) ATI TV Wonder Value Edition PCI (TV-Tuner and Video Capture) (4) 3Com/US Robotics 56Kbps VOICE/FAX modem PCI (5) ADI AD1888 SoundMAX 6-channel audio with S/PDIF interface (onboard) (6) Marvell 88E8001 Gigabit LAN adapter (onboard) Here's a sample config: AGP = Asus PCI 1 = ati tv PCI 2 = visiontek PCI 3 = modem Question: Since I will be using the modem ONLY for sending and receiving Faxes, why would you place it in PCI 3 giving it a dedicated IRQ? I've always understood that sharing IRQs with two or more high-data throughput devices would impair performance. You've got the two graphics cards sharing an IRQ (on PCI-2 and the AGP). I was going to "share" the modem with the onboard LAN since the modem would not be used very much. I was going to leave PCI-2 and PCI-5 unused to get the maximum performance out of the AGP for game play. Oh, and thanks for the excellent description of how the interrupt controller actually works! - Gordon |
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