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From: desmond@smaug.dec.com
Newsgroups: comp.sys.ibm.pc
Subject: MSC medium model TSR questions
Message-ID: <8711130253.AA04513@decwrl.dec.com>
Date: Thu, 12-Nov-87 21:53:00 EST
Article-I.D.: decwrl.8711130253.AA04513
Posted: Thu Nov 12 21:53:00 1987
Date-Received: Sun, 15-Nov-87 03:09:16 EST
Organization: Digital Equipment Corporation
Lines: 30

I am working on a program that I want to terminate and stay resident and
I have several questions that I would like answers to.  First some background.
The program will be written in a combination of Microsoft C v4.0 and 8086
assembly.  It will be compiled under medium model in C and the .EXE will
be approximately 200K.  Now the questions:

1)  How does one figure out where to mark the end of resident memory?  I
    believe all data is loaded above the code so in small model I would
    probably be safe to take the address in DS plus 64K as the end of the
    image but what about the stack?  Also since this is a medium model
    program, where are the far data elements loaded and how can I find out
    the highest address needed by my program after termination?

2)  Once the program is resident, can it be terminated a second time with
    a normal exit thereby releasing all of its memory back to the system?
    Or is the only way to get back all available memory a reboot?  I know
    there are some PD utilities that supposedly remove TSRs but I don't
    want to use something like that.  I want a way for my program to remove
    itself if possible.

3)  If after termination, the resident C code does some calls to malloc(),
    how is that allocation handled?  If I confine my malloc calls to only
    near data, will all the data which is dynamically allocated come from
    my data segment?  The problem is that once I terminate and give back
    all the memory I'm not using, some other application may take it.  I
    don't want my malloc calls to fail because of insufficient memory.

I would appreciate any information about these questions and anything else
I should know about writing a TSR.  Thanks.

						John