Turbo-3 Overlay Files 
Author Message
 Turbo-3 Overlay Files

Hi all.

I am using overlayed procedures in a Turbo-3 (for CP/M) application
on a handheld computer such that various modes of operation load
their corresponding code from the overlay.  Now as it happens, most
of these modes are mutually exclusive so, to save disk space (which
is at a premium on the handheld being used), what I'd like to do is
somehow compile different versions of the overlay file with only the
relevant code for that mode but with EXACTLY the same main file.

Not really explained too well - Let me try a picture...
(Hope you are using a monospaced font)

      MAIN.COM       MAIN.000        MAIN.001       MAIN.002
                   +----------+    +----------+   +----------+
    +----------+  /|  MODE 1  |    |  MODE 1  |   |  MODE 2  |
    |   MAIN   | / +----------+    |          |   +----------+
    +----------+/  |  MODE 2  |    +----------+   |  COMMON  |
    |  OVERLAY |   +----------+    |  COMMON  |   +----------+
    +----------+\  |  MODE 3  |    +----------+
    |   MAIN   | \ +----------+
    +----------+  \|  COMMON  |

I want to be able to somehow split MAIN.000 into MAIN.001, MAIN.002
and MAIN.003 (one file for each mode procedure overlay).  A slight
spanner in the works is that there are also a couple of overlay
procedures which should be COMMON to all three files.

What I've tried so far:
I compiled three versions of the application, each with only the
required mode.  I then recompiled using the mode which created the
LARGEST overlay file, hoping that this would reserve enough space
for the code in MAIN so that I could use any version of the overlay
file (renamed to MAIN.000 of course) and it could be accommodated.
Unfortunately, forward references to the end code get confused when
smaller overlay files are loaded.  (I'm not sure what these refs are
but suffice to say - it didn't work).

Does anyone have any ideas (assuming my explanation was ok - I'm
battling to understand what I wrote myself!) or know any details
of the internal format of the overlay file that I may be able to
use to my advantage?

Many thanx
Lester Hanger
Johannesburg, South Africa

Wed, 18 Jun 1902 08:00:00 GMT  
 [ 1 post ] 

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