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From: everett@hpcvlo.HP.COM (Everett Kaser)
Newsgroups: comp.sys.ibm.pc
Subject: Re: DOS Critical-error handler
Message-ID: <1610024@hpcvlo.HP.COM>
Date: Fri, 31-Jul-87 17:42:32 EDT
Article-I.D.: hpcvlo.1610024
Posted: Fri Jul 31 17:42:32 1987
Date-Received: Sun, 2-Aug-87 09:48:05 EDT
References: <1871@isis.UUCP>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 19

>Here is my Idea of a Critical Error Handler. It sets carry for the
>int 21 caller and sets the return in AX to 100..10C for the caller to know
>that a hard error occured.
>
>INTERRUPT_24	PROC	FAR
>		ADD	SP,6			; Dump Dos Return
>		MOV	BP,SP

Something you should be aware of is that if you bail out of the critical
error interrupt this way, (i.e. you're not returning back through DOS) you're
leaving DOS in an unstable state.  When this happens, the next call to DOS
must be a call below (I think) about 0ch. (i.e. one of the simple console I/O
routines, such as check for key.)  If not, if you try doing disk I/O or
something immediately after this bail-out, DOS will be confused as to what
state it's in, and you may get very unwanted behaviour.

Everett Kaser
Hewlett-Packard Co.
Corvallis, OR