Cpu

sujanne · May 25, 2010

How can the CPU obtain the starting address of the appropriate interrupt service routine in each case? Since different devices are likely to require different interrupt service routines, how can the CPU obtain the starting address of the appropriate routine in each case ?

Burrell · May 25, 2010

I found two answers on the net, as i know nothing on the subject, i cannot comment on their reliability.

The addresses of service routines are stored in low memory addresses. Get a hardware manual that describe the interrupt routine.

If my memory is accurate, I believe 8088 and 80186 chips store interrupts as 4-byte vectors beginning at address 0x0000. 32-bit and 64-bit chips will use larger vectors.
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There are two common methods which effectively work out the same:

1) The CPU looks up the appropriate starting address in a table that is kept at a fixed location in memory.

2) The CPU always starts at a fixed address, usually spaced just a few bytes apart. Typically, all you put at that address is a jump instruction to the address of the appropriate handler. (But you can put a 'return' instruction to ignore the interrupt.)
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Cpu

sujanne Private E-2

Burrell MajorGeek