What Happens When A Hardware Interrupt Is Generated?

[jayron 0]

The operations that take place when a hardware interrupt occurs are as follows:1.A special chip called Interrupt Controller chip receives the interrupt signal.2.The Interrupt Controller chip notifies the microprocessor that an interrupt has occurred.3.To keep track of what microprocessor was doing before it was interrupted, it saves the contents of registers CS, IP and Flags in stack.4.The microprocessor retrieves the number of the interrupt from the Interrupt Controller chip.5.Having found out the interrupt number, it multiplies this number by four (since each address in IVT is 4 bytes long), then goes to the Interrupt Vector Table (IVT) and finds out the address of the corresponding ISR.6.Once the ISR has completed it execution it issues an IRET instruction. As a result, the microprocessor pops the values that were earlier pushed onto the stack, back into CS, IP and Flags registers. From the values in CS:IP microprocessor comes to know which activity it was performing before the interrupt occurred.7.Microprocessor now resumes its interrupted activity.

[kdr_98 0]

Nice text.But only with the old ISA cards you have to setup the IRQ manualy by a dipswitch.These days everything is mananged by PnP.Only in a case of confict , you can setup the IRQ in Windows Manualy.Some IRQ are standard like IRQ 3,4 For serial ports and IRQ 7 for LPT ports.But even those are getting old dated.So in a 'modern' computer there is no need of setup an IRQ , You just plug in the 'new' card and hope it gets right detected by 'Plug and Play'. If not you can fix somethings manually, but a basic knowledge of your BIOS is required for that.