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RE: what happens if 2 INTs occur at same time
Many thanks to Thomas J. Merritt. This information really helps in
bringing forward our project. In general literature spend a lot of time
to describe the interrupt behavior based on PC architecture. It doesn't
come to my mind that the interruptackn. cycle isn't a must.
ADVA AG (cellware broardband)
tel. +49-30-670 080 167
fax. +49-30-670 080 108
> -----Original Message-----
> From: Thomas J. Merritt [mailto:email@example.com]
> Sent: Thursday, April 13, 2000 4:23 PM
> To: Jürgen Klemt
> Cc: PCI Mailing List
> Subject: Re: what happens if 2 INTs occur at same time
> The first confusion is that an interrupt acknowledge cycle will or needs
> to be done after the interrupt line is raised. The interrupt ack cycle
> are primarily for backwards compatability with older PC hardware. In
> these system the 8259 interrupt controler was across the PCI bus and in
> order for the processesor interrupt ack cycles to get to the 8259 they
> needed to traverse the PCI bus. The mechanism used is the interrupt
> ack. PCI cycle. The interrupt ack mechanism is only used for getting
> interrupt vectors from an interrupt controller and is NOT used for
> getting a vector from an interrupting device. Your CPCI boards will
> not be generating vectors. See the EPIC section of the 8240 users manual
> for the details on 8240 interrupt handling..
> If the CPCI interrupt lines will be routed to the 8240 with the 8240
> in direct IRQ mode then, if two interrupt sources kick the same line
> at the same time the 8240 will vector to just one interrupt service routine.
> In that interrupt service routine you will need to check both devices that
> are connected on that line for an interrupt condition. In general
> interrupt handling logic looks like the following.
> struct handler_info *handlers;
> for (handlers = interrupt_handlers[INTERRUPT_IRQ0]; handlers;
> handlers = handlers->next)
> Then in your interrupt handler you might do something like the following.
> device_interrupt_handler(struct device_info *dev)
> while (1)
> int interrupts = dev->regs[DEV_INTERRUPT_STATUS];
> if (!interrupts)
> if (interrupts & DEV_INTERRUPT_CONDITION1_BIT)
> /* handle interrupt condition 1 here */
> else if (interrupts & DEV_INTERRUPT_CONDITION2_BIT)
> /* handle interrupt condition 2 here */
> Thomas J. Merritt
> Software Consultant
> CodeGen, Inc.