How to create an interrupt table

Question

I have a homework assignment for my Operating Systems class where I need to write an interrupt table for a simulated OS. I already have, from a previous assignment, the appropriate drivers all set up:

My understanding is that I should have an array of interrupt types, along the lines of interrupt_table[x], where x = 0 for a trap, x = 1 for a clock interrupt, etc. The interrupt_table should contain pointers to the appropriate handlers for each type of interrupt, which should then call the appropriate driver? Am I understanding this correctly? Could anyone point me in the right direction for creating those handlers?

Thanks for the help.

Jerry Coffin · Accepted Answer · 2011-02-28 04:36:25Z

2

Most details about interrupt handlers vary with the OS. The only thing that's close to universal is that you typically want to do as little as you can reasonably get away with in the interrupt handler itself. Typically, you just acknowledge the interrupt, record enough about the input to be able to deal with it when you're ready, and return. Everything else is done separately.

answered Feb 28, 2011 at 4:36

Jerry Coffin

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sarnold · Accepted Answer · 2011-02-28 04:37:01Z

1

Your understanding sounds pretty good.

Just how simulated is this simulated OS? If it runs entirely on a 'machine' of your professor's own design, then doubtless she's given some specifications about what interrupts are provided, how to probe for interrupts that may be there, and what sorts of tasks interrupt handlers should do.

If it is for a full-blown x86 computer or something similar, perhaps the Linux arch/x86/pci/irq.c can provide you with tips.

answered Feb 28, 2011 at 4:37

sarnold

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user637290 · Accepted Answer · 2011-02-28 07:30:05Z

What you do upon receiving interrupt depends on the particular interrupt. The thumb rule is to find out what is critical that needs to be attended to for the particular interrupt, then do "just" that (nothing more nothing less) and come out of the handler as soon as possible. Also, the interrupt handlers are just a small part of your driver (that is how you should design). For example, if you receive an interrupt for an incoming byte on some serial port, then you just read the byte off the in-register and put it on some "volatile" variable, wind up things and get out of the handler. The rest (like, what you will do with the incoming byte on the serial port) can be handled in the driver code.

The thumb rule remains: "nothing more, nothing less"

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