Path: utzoo!utgpu!water!watmath!clyde!rutgers!rochester!PT.CS.CMU.EDU!B.GP.CS.CMU.EDU!Ralf.Brown@B.GP.CS.CMU.EDU
From: Ralf.Brown@B.GP.CS.CMU.EDU
Newsgroups: comp.sys.ibm.pc
Subject: Re: What's the deal on the 80387 and real mode interrupts?
Message-ID: <21e646ac@ralf.home>
Date: 9 Jan 88 15:11:40 GMT
Sender: netnews@PT.CS.CMU.EDU
Lines: 16
In-Reply-To: <2730@killer.UUCP>

In article  <2730@killer.UUCP>,  richardh@killer.UUCP (Richard Hargrove) writes:
}This actually caused some problems for the early AT BIOS implemenatations
}because the 80286 claimed some of the reserved interrupts (the BOUND 
}instruction traps to interrupt 5 if the tested value is out of the specified
}bounds, and we all know what's at INT 5 - the print-screen driver!) and the
}BIOS code wasn't written to handle them! The BOUND instruction could call
}the INT 5 routine with random parameters!

What's worse, the BOUND exception is restartable--the handler is supposed to
correct the condition (if possible), and then the BOUND instruction is re-
executed on return.  Since the print-screen handler doesn't take any
parameters or modify any registers, the INT 5 is called again, and again, and...

}richard hargrove
}...!killer!richardh
}-------------------