Path: utzoo!utgpu!water!watmath!looking!brad
From: brad@looking.UUCP (Brad Templeton)
Newsgroups: comp.sys.ibm.pc
Subject: Re: What's the deal on the 80387 and real mode interrupts?
Message-ID: <1282@looking.UUCP>
Date: 5 Jan 88 16:17:37 GMT
References: <1269@looking.UUCP> <8349@steinmetz.steinmetz.UUCP>
Reply-To: brad@looking.UUCP (Brad Templeton)
Organization: Looking Glass Software Ltd.
Lines: 24

In article <8349@steinmetz.steinmetz.UUCP> davidsen@crdos1.UUCP (bill davidsen) writes:
>In article <1269@looking.UUCP> brad@looking.UUCP (Brad Templeton) writes:
>| My documentation on the 387 states that an exception triggers trap 16 (decimal)
>| in the 386.   If this maps into the 16th vector in real mode, as it seems to,
>| this is the same as IBM's VIDEO Bios call!
>
>Looking at the original 8086 product manual, it clearly states that
>interrupts 0-31 are reserved to Intel for expansion, and int 224 is
>reserved to Digital Research for CP/M-86. There is a conflict, and it's
>because Microsoft/IBM messed up. Yes, you can get problems here.
>-- 

Ok, so what do we do if we want to write a general exception handler for
all these machines?

What do the clones do?  Do most of them map this exception in real mode to
the old IRQ 13 on the 286?  I know that a 287 in my 386 seems to do this.
What do the Compaq Deskpro 386 and PS/2 model 80 do about this?

My clone seems to call *both* IRQ 13 and Int 16.  Do others do this?
Is the only solution to write an interceptor for the BIOS call that checks
the trap flag in the 387?  Yuck.
-- 
Brad Templeton, Looking Glass Software Ltd. - Waterloo, Ontario 519/884-7473