Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!agate!pasteur!ames!hc!lanl!opus!dante!pgaughan
From: pgaughan@dante.nmsu.edu (Patrick Gaughan)
Newsgroups: comp.sys.ibm.pc
Subject: Re: More assembly questions about TSR development.
Keywords: TSR, .EXE
Message-ID: <210@opus.NMSU.EDU>
Date: 27 Apr 89 16:08:34 GMT
References: <4550@tekigm2.MEN.TEK.COM>
Sender: news@nmsu.edu
Reply-To: pgaughan@dante.UUCP (Patrick Gaughan)
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Organization: New Mexico State University
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Q: Can a TSR be an .EXE?

Yes.

Q: Why is there no stack segment defined in the TSR source listings I've seen?

The TSR listings you have been looking through have been .COM TSR's.  In a 
.COM file there can only be one segment and CS, DS, ES, and SS all point to
that segment on program startup.  EXE2BIN will not work if more than one
segment is defined.  But, if you want your TSR to be a .EXE, don't bother 
to use EXE2BIN.  

Also, a few more differences between .COM's and .EXE's:
  .COM's have a ORG 100h at the beginning of the code segment to make room
         for the PSP (Program Segment Prefix).  .EXE's do not need this 
         since DOS allocates a PSP for them on startup.
  .EXE's can have an entry point anywhere within the code segment while .COM's
         must start at 100h (right after the ORG).
  Since .COM files are limited to 1 segment, this generally implies 64k is the
         limit on the size of the final code (although I'm sure there is a way
         around this...)

Also, when developing TSR's, using DOS function calls (INT 21h) on interrupt 
is a very tricky business and many articles should be read before doing it
yourself...

Suggested references:
PC magazine - whenever they have a TSR utility, read the article
DOS Technical Reference Manual
The Waite Group's MS-DOS Developer's Guide
MS-DOS Advanced Programming

Disclaimer:"I know NOTHING! NOTHING!" (German accent implied...)

Brought to you by the developer of TSR NCSA Telnet,
(Please don't flood me with mail, a 256k TSR is not that useful yet...)

Patrick Gaughan		Programmer of Gor
pgaughan@nmsu.edu	New Mexico State University