Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!dimacs.rutgers.edu!mips!daver!vsi1!octopus!stever
From: stever@Octopus.COM (Steve Resnick )
Newsgroups: comp.os.msdos.programmer
Subject: Re: Is BIOS Reentrant?
Message-ID: <1990Nov14.210348.27367@Octopus.COM>
Date: 14 Nov 90 21:03:48 GMT
References: <4844@trantor.harris-atd.com> <11569@hubcap.clemson.edu> <2893@gmuvax2.gmu.edu>
Reply-To: stever@octopus.UUCP (Steve Resnick )
Distribution: na
Organization: Octopus Enterprises, Cupertino CA
Lines: 33

In article <2893@gmuvax2.gmu.edu> 2113av@gmuvax2.UUCP (John Porter) writes:
>In article <11569@hubcap.clemson.edu> lsalomo@hubcap.clemson.edu (lsalomo) writes:
>>but I do believe that you can use up to int 9 with no problems (someone else
>>better verify this).
>
>YAHHH! What do you mean by "use" up to int 9? Those are interrupts are 
>hardware-generated; you might program a handler for them, but you should
>never call them.  The question is, what interrupts can you call while
>handling an interrupt.  Many BIOS interrupts don't care how deeply you
>nest calls to them.  Results may be unpredictable, but at least you won't
>snocker the system, unlike with many DOS calls.
>--jp

With the exception of INT 05, all interrupts < 10H are hardware generated. 
Int 05 is generated by the int 9 ISR upon make/break of the print screen key.
Calling hardware interrupts via software is generally not a good idea, since
the ISR is expecting to diddle the 8259 PIC and maybe other hardware as well.
Think, also, about what might happen if you call int 0EH (floppy interrupt)
via software and a hardware floppy interrupt occurs? If the ISR didn't 
disable interrupts, and the 8259 puts a int 0eH on the bus, you may really
mung your floppy... 

BTW - You can call int 5 (print screen) via software with no ill effects.


-- Steve


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