Creating Code with Absolute Addresses

Your TechKit includes a program, TSLOCATE.EXE, that enables you to
specify exactly where the various segments of your program are to
be placed. This can be very useful for creating embedded programs,
for putting your programs in PROM's or for making a bootable disk for a
program that is to run without DOS.

TSLOCATE is used to locate an MSDOS EXE-file.  That is,
the segments are allocated absolute segment values in the 8086
1-Mbyte memory space.  The output is the binary image of the
program.

The memory layout for the target system is specified in the
.MEM file, together with the linker classes which are to be
put in the memory. For example:

ram   100  60000 DATA Dummy BSS M_DATA STACK HEAP
rom F8000  FFFF0 CODE F_CODE
rom FFFF0 100000 BOOTCODE
width 2

Each line of the .MEM file must start with rom, ram or
width.

For rom and ram lines, these words are followed by two
hexadecimal numbers, specifying the start and end absolute addresses
of some memory in the target system configuration. The second address is a
`stop' address, so that a warning can be produced if there is not
enough memory. The addresses are followed by a list of class
names, separated by spaces. The order of the names is not significant
(the ordering is determined by the order in the link).

The word width is followed by a number which should be 1, 2 or
4.  The default is 1.  This number specifies the target data bus
width, in bytes.  For example, width 2 indicates that the
target data bus is 2 bytes wide, and causes two binary files to be
produced --- one with the even bytes, one with the odd bytes. This is
necessary because PROMs are normally only 1 byte wide, so in a system
with a 16-bit data bus at least 2 PROMs will be required.

TSLOCATE is invoked with a single parameter --- the file name,
but not including the extension. For example

tslocate myprog

When invoked, TSLOCATE uses three input files:


MYPROG.EXE
the msdos excutable file

MYPROG.MAP
the map produced by the linker

MYPROG.MEM
the ASCII file specifying the memory layout


The output files from TSLOCATE are:



MYPROG.BN?
the binary image(s)

MYPROG.MP2
the .MAP file with edited addresses

Certain environments may have unusual code location requirements.
One hint to keep in mind when dealing with such cases is the following:
If the class names in the map file prove to be too "coarse," you can
always edit the map file to change the class name for certain segments.

Putting Things in (P)ROM
The following considerations are important if you need to put
code into ROM or into PROM

Special arrangements must be made for segments which are initialised
and subsequently modified. Probably the easiest method to start with
is to avoid this situation, possibly by using the data pragma to specify
that the initialised variables are placed in seperate segments, and not
attempting to modify them. Note that string and floating point
literals are equivalent to initialised data.

An alternative idea is to run tslocate twice, the first time
to create the code image, the second time to create the initialised
data image. Then when the rom program starts execution it should copy
the region of prom where the initialised data image is stored into
the ram location where it is required during execution.

Startup code for embedded systems
=================================

The INITESYS.A file is in the SRC directory.

Your project should include initesys,corertl and coremain. Functions may also be
imported from language standard libraries.

1) Do not use #link, as the point using INITESYS instead of INITEXE
   is to avoid bringing in all the standard library code. Instead, include
   a #compile for each part of the library that is required, then use
   #dolink.

2) In the module INITESYS.A the last line has 'end *', the * character
   being a command to the assembler to indicate the entry point.

For example, if you have an assembler file V25LIB.A which implements some
functions for your embedded system and has no initialization code, your
project would look like this:

         ----------- EMBEDDED.MOD ------------------
         MODULE Embedded;
         IMPORT V25Lib;

         BEGIN
         .
         END Embedded.

         ------------- V25LIB.DEF ------------------
         (*# module( init_code => off) *)
         DEFINITION MODULE V25Lib;
         .
         END V25Lib.

         ------------ V25LIB.A -------------------
         .
         .
         .

         ----------- EMBEDDED.PR -----------------
         #system dos exe
         #model small jpi

         #compile initesys.a
         #compile embedded.mod
         #compile v25lib.a
         #compile coremain.a
         #compile corertl.a  -- ditto for other required system independent
                             -- parts of modula library
         #dolink embedded
         #run "tslocate embedded"