From:	Psilon AT concentric DOT net (Avery Lee)
Newsgroups:	alt.msdos.programmer,comp.os.msdos.djgpp,comp.os.msdos.programmer
Subject:	Re: IRQ trap with stack change, very intersting!
Date:	Sat, 05 Jul 1997 00:36:38 GMT
Organization:	Concentric Internet Services
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To:	djgpp AT delorie DOT com
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Roberto Garza <robgarza AT infosel DOT net DOT mx> wrote:

>> I want to write a dual-task program. Each time the interrupt come, i want
>> to do a stack switch (íve provided 2 separated stacks, allocated at
>> start-time), save the registers, change the return CS:IP in the stack to
>> point to the next task and, then, do an IRET.

It is not possible to do task switching in this manner with DPMI.  DPMI
servers may give you a completely separate stack when the interrupt
strikes, and you cannot look up the stack to find out where your program
was interrupted, especially since the interrupt may not have struck when
your program was running.  The DPMI specification says, I believe, that it
is not intended to allow client programs to multitask themselves.


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