Hi Thomas, On 12/30/05, Thomas Petazzoni <thomas.petazzoni@xxxxxxxx> wrote: > Hi > > [ Top-posting is a bad idea. Please don't. See > http://en.wikipedia.org/wiki/Top-post ] I forgot about it. anyway will do it from now on. > Bhanu Kalyan Chetlapalli wrote: > > > The Processor gets interrupts through the PIC 8259A. Hence > > during bootup we reprogram the 8259A to remap the IRQs from 0-31 range > > to a more reasonable range. > > I'm not sure of the state of the 8259A at bootup (not sure it maps IRQs > to interrupts 0-31), but anyway, you need to program it to redirect IRQs > to a range of processor interrupts that are available. > > > For Example if we have an interrupt for an NIC, it will be shown as, > > lets say, 17 in the PCI config space. But the 8259A (when we reprogram > > it manually in the kernel) will remap it to some value like 49 or so. > > So while registering the IRQ we use the same number 17 only to > > register it. which is why ifconfig & /proc/interrupts show the number > > - 17. The actual interrupt handler descriptor is placed at Index of 49 > > in the IDT. > > You got it. There is just one more doubt. When we recieve an interrupt and the interrupt handler function (which we give in request_irq) is called, We are passed a number of the IRQ. i.e. in the prototype for the handler, the - int irq. irqreturn_t tulip_interrupt(int irq, void *dev_instance, struct pt_regs *regs) This number corresponds to the number - 17 (from the prev analogy). So does the kernel convert the number 49, when an interrupt occurs, back into 17 and give it to the handler? Does the kernel maintain a mapping somewhere? can you give me a pointer to the kernel code which does this? > > Sincerly, > > Thomas > -- > Thomas Petazzoni > thomas.petazzoni@xxxxxxxx > > -- > Kernelnewbies: Help each other learn about the Linux kernel. > Archive: http://mail.nl.linux.org/kernelnewbies/ > FAQ: http://kernelnewbies.org/faq/ > > Thanks & Regards, Bhanu. -- The difference between Theory and Practice is more so in Practice than in Theory. -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
