Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!umd5!rutgers!clyde!watmath!looking!brad
From: brad@looking.UUCP (Brad Templeton)
Newsgroups: comp.sys.ibm.pc
Subject: What's the deal on the 80387 and real mode interrupts?
Message-ID: <1269@looking.UUCP>
Date: 2 Jan 88 02:51:52 GMT
Organization: Looking Glass Software, Waterloo Ont.
Lines: 20

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!

I wonder because some 387 software I am testing seems to clear the screen
sometimes on a numeric exception!

The 287 (which can also be used with a 386) triggers what they call an IRQ 13,
which somehow becomes an INT 75 on an AT style machine.  The code for INT 75
just resets the 287 and calls INT 2, the NMI vector.  (On the PC, IBM wired
the 8087 exception line to NMI.)

Anyway, all this makes writing a good general exception handler for all three
Intel 80x87 chips a tad complicated.  Could the screen clear be the result
of a hardware bug in the 386 board?  Is it even possible to stop the 80387
exception from triggering an INT 16?

Any info would be appreciated.
-- 
Brad Templeton, Looking Glass Software Ltd. - Waterloo, Ontario 519/884-7473