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From: ralf@B.GP.CS.CMU.EDU (Ralf Brown)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Undocumented 34h Call
Message-ID: <366@PT.CS.CMU.EDU>
Date: Tue, 17-Nov-87 20:07:46 EST
Article-I.D.: PT.366
Posted: Tue Nov 17 20:07:46 1987
Date-Received: Fri, 20-Nov-87 03:32:23 EST
References: <558@wolf.UUCP>
Sender: netnews@PT.CS.CMU.EDU
Organization: Carnegie-Mellon University, CS/RI
Lines: 25
Keywords: TSR,Critical Section Flag

In article <558@wolf.UUCP> markd@wolf.UUCP (Mark Divecchio) writes:
}[...] "Depending on the DOS version, you should
}check the byte after (DOS 2.1), before (DOS 3.0 and 3.1, if not
}Compaq-DOS), or 01AAH bytes before (Compaq-DOS 3.0). You should
}check to make sure that you're not in the middle of a BIOS interrupt
}13h (Disk I/O) or 16h (Keyboard Service Request)."
}---------------------------------
}Mark C. DiVecchio 10435 Mountain Glen Terrace, San Diego, CA 92131
}sdcsvax!man!wolf!markd                   Bulletin Board 619-549-3927

The first sentence quoted above refers to a second byte that you should
check *in addition* to the byte pointed to by the address returned by the
INT 21/AH=34h function call.

The only way to check whether you're in the middle of an INT 13h or INT 16h is
to hook yourself into these interrupts.  Your routine needs to set a flag, 
call the original interrupt handler, reset the flag, and return.



-- 
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