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From: dmurdoch@watstat.waterloo.edu (Duncan Murdoch)
Newsgroups: comp.lang.pascal,comp.os.msdos.programmer
Subject: Writing a device driver in TP
Message-ID: <1991May29.140429.11384@maytag.waterloo.edu>
Date: 29 May 91 14:04:29 GMT
Sender: news@maytag.waterloo.edu (News Owner)
Organization: University of Waterloo
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I've heard (and said!) repeatedly that it's impossible to write a DOS device
driver in Turbo Pascal.  Not true - I've written a simple one entirely in
TP 6, and uploaded it to garbo.uwasa.fi (TPDEV.ZIP).  It would be harder,
but probably possible, to do the same thing in earlier versions of TP.
I imagine it would require careful byte counting, external assembler code,
patching, or some other trick I can't think of.  TP 6 has the inline
assembler, assembler procedures, and allows constants to be initialized with
the address of code, so it was relatively easy there.

Take a look at it.   It makes prototyping a device driver much easier than
writing it from scratch in assembler.

One limitation:  it produces .EXE format drivers.  I asked the other day about
limitations on these, and got two responses:

 - They work in MSDOS, but not PCDOS, because the .EXE loader is part of
   COMMAND.COM in PCDOS.
 - They only work in version 3 or higher.

Thanks to those who responded!  I can confirm that the .EXE format is
fine in MSDOS 3.2, but haven't tested it anywhere else.

Duncan Murdoch
dmurdoch@watstat.waterloo.edu