IRQ Sharing In Action

Post #1,395 by pwhysall 7/11/01 3:07:09 AM Reply	IRQ Sharing In Action Here's my IRQ layout, as reported by Windows 2000: IRQ Number\tDevice 9\tMicrosoft ACPI-Compliant System 11\tNVIDIA RIVA TNT2/TNT2 Pro 11\tIntel 82371AB/EB PCI to USB Universal Host Controller 11\tVortex Multifunction PCI Parent 11\tAureal Vortex 8830 Audio (WDM) 11\t3Com EtherLink XL PCI TPC NIC (3C900B-TPC) #2 11\tMass Storage Controller 15\tSecondary IDE Channel 8\tSystem CMOS/real time clock 13\tNumeric data processor 6\tStandard floppy disk controller 4\tCommunications Port (COM1) 3\tCommunications Port (COM2) 1\tStandard 101/102-Key or Microsoft Natural PS/2 Keyboard Note all that stuff going through IRQ 11. I'll also free up another IRQ when I gets me a PS/2 -> USB adapter for this here IBM keyboard. -- Peter Shill For Hire
Post #1,663 by a6l6e6x 7/13/01 12:16:19 AM Reply	Re: IRQ Sharing is a two edged sword. It's nice that a number of devices can share an interrupt - you can have more devices. It's bad because when an interrupt occurs, you don't know who (i.e. which device) caused it or why. On an interrupt, additional interrupts are automatically disabled - interrupt handlers aren't themselves interrupted. The interrupt handlers of the associated device drivers for an IRQ are started one at a time, probably in the same sequence each time, and interrogate the associated device to see if it was the one that caused the interrupt. If not, the next device's interrupt handler is started. If so, the event is recorded, the interrupt condition in that device is reset, the next operation if any may be started, and interrupts re-enabled. If other devices had a pending interrupt the interrupt handling process (as above) would start again. Otherwise, whatever process was originally interrupted would resume. The disadvantages of sharing interrupts are that 1) it takes longer to figure out what caused an interrupt and 2) that some devices, in effect, get preferential treatment. For good performance, it's important to arrange the sequence of device drivers so that the most frequently interrupting devices are serviced earlier. Alex
Post #2,173 by SpiceWare 7/17/01 11:49:10 PM Reply	Amiga also shared IRQs The IRQ number was related to the priority of the interrupt. I recall that the serial port operated on 2 IRQs - the higher priority IRQ was for receiving, the lower one for sending. Darrell Spice, Jr. [link\|http://home.houston.rr.com/spiceware/\|SpiceWare] - We don't do Windows, it's too much of a chore

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