Editing OS-9 Assembly Code Development (section)

=== Program Modules ===
The format of a program module varies depending on whether you have a single source file for your program or multiple source files.  

Note: multiple source files format cannot use direct page addressing due to the way they are compiled.

==== Single Source File Format ====
The following is a skeleton for a single source file memory module (program).
 <code>********************************************************************</code>
 <code>* [Program Name]</code>
 <code>* [Description]</code>
 <code>*</code>
 <code>* by [Author Name]</code>
 <code>*</code>
 <code>* Edt/Rev  YYYY/MM/DD  Modified by</code>
 <code>* Comment</code>
 <code>* ------------------------------------------------------------------</code>
 <code>               nam       [executablename]</code>
 <code>               ttl       [Full Program Name]</code>
 
 <code>               ifp1</code>
 <code>               use       defsfile</code>
 <code>               endc</code>
 
 <code>tylg           set       Prgrm+Objct</code>
 <code>atrv           set       ReEnt+rev</code>
 <code>rev            set       $00</code>
 <code>edition        set       1</code>
 
 <code>               '''mod       eom,name,tylg,atrv,start,size'''</code>
 
 <code>        [Data Section - Variables and Data Structures Here]</code>
 
 <code>size           equ       .</code>
 <code>name           fcs       /[executablename]/</code>
 <code>               fcb       edition</code>
 
 <code>start</code>
 
 <code>        [Program Section - Program Code Here]</code>
 <code>        </code>
 <code>               os9       F$Exit</code>
 
 <code>               '''emod'''</code>
 <code>eom            equ *</code>
 <code>               end</code>
OS9 can load programs (modules) only if they are in module header format.  A module (program) is defined between the '''mod''' and '''emod''' pseudo instructions.

* '''mod:''' Creates the module header and starts CRC check. '''mod''' has 6 attributes:

# Module size (computed from the ''<u>eom</u>'' label at the end of the code - 2 bytes)
# Module name offset (offset where the string of the name is contained, here that is defined at the ''<u>name</u>'' label with the ''fcs'' pseudo instruction - 2 bytes
# Module type & language (in this case a Program in 6809 object code - 1 byte)
# Module attribute-revision (1 byte).  Attributes are reentrant (ReEnt) or not reentrant  (0).  Revision is a number 0-15.  If two or more modules with the same name are in the module directory, then OS-9 only keeps the highest revision number module.
# Module execution offset (here that is defined with the ''<u>start</u>'' label - 2 bytes)
# Module variable storage size (defined by the ''<u>size</u>'' label immediately after the variable area, includes stack space - 2 bytes)

* '''emod''': Outputs the correct 3 byte CRC.  This is generated by the assembler over the entire module.


For more information about memory modules, see OS-9 Fundamentals:

[https://www.youtube.com/watch?v=YpoqTyrty8k OS-9 Fundamentals on YouTube by Boisy Pitre]

==== Multiple Source File Format ====