Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!elroy.jpl.nasa.gov!jato!mars!schmidt
From: schmidt@mars.jpl.nasa.gov (Kevin Schmidt)
Newsgroups: comp.os.msdos.programmer
Subject: Re: stealing an interrupt
Message-ID: <1990Dec18.163810.21268@jato.jpl.nasa.gov>
Date: 18 Dec 90 16:38:10 GMT
References: <90351.150210TOMIII@MTUS5.BITNET>
Sender: news@jato.jpl.nasa.gov
Reply-To: schmidt@mars.UUCP (Kevin Schmidt)
Organization: Jet Propulsion Laboratory, Pasadena, CA.
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In article <90351.150210TOMIII@MTUS5.BITNET> TOMIII@MTUS5.BITNET (Thomas Dwyer III) writes:
>Hi there.  Would some kind soul please tell me why my machine hangs when
>I run this TSR?  What am I doing wrong?
>
>------ Code Deleted ------
>
Code that was here got INT 9 vector and put it in old_int.  It then set
the INT 9 vector to point to new_int.
>
>new_int proc    far
>        jmp     short go
>
>old_int dd      ?
>
>go:
>        jmp     [old_int]                       ; Jump to old int routine
>new_int endp
>
>----- Code Ends ------
>
Everything looks fine except that the last jump (jmp [old_int]) has two
problems.  First the jump must include a segment override so that the
data segment (ds) is not used in calculating the address of old_int.
Second you must insure that it is a far jump.  Thus the line should read:

   jmp far cs:[old_int]

If you still can't get it to work, email me and I will send you a sample
of how to attach to INT 9.
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       / / / _  \  / /  | Kevin T. Schmidt          | schmidt@mars.jpl.nasa.gov
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