interruptable machine instructions

[AliMH]

do you know what are interruptable machine instructions?
PLS help me :(

[Phil]

Wow, that sounds like a really good question! Are you speaking of instructions that can start execution but then be interrupted before completion? I'd guess any of the REP MOVSB and things of that nature ... maybe even DIV and other long instructions could be interrupted before completion then safely restarted when the interrupt is dismised. I'm not sure that I understood the nature of your question?

[hutch--]

Ali,

I am very rusty here as I have not worked in REAL mode for a very long time but from memory at least some instructions would fail if an interrupt occurred while they were running. You would tend to have to look at very old DOS code to see this stuff and as this is a 32 bit Windows forum, its not really the place to do it.

I have moved this posting to the 16 bit forum so you have more chance of an answer.

[MichaelW]

AFAIK only repeat string instructions can be interrupted -- all other instructions are executed to completion before the interrupt is serviced. From the IA-32 Intel Architecture Software Developer's Manual, Volume 2B: Instruction Set Reference, N-Z:

A repeating string operation can be suspended by an exception or interrupt. When this happens, the state of the registers is preserved to allow the string operation to be resumed upon a return from the exception or interrupt handler. The source and destination registers point to the next string elements to be operated on, the EIP register points to the string instruction, and the ECX register has the value it held following the last successful iteration of the instruction. This mechanism allows long string operations to proceed without affecting the interrupt response time of the system.