OS-9 Assembly Code Development

Overview

Each process in NitrOS9 is allocated its own 64K address space. When run, the program object code is loaded into one memory space, and the variables and data structures are loaded into the other. This includes separate execution and data directories and std in, std out and std err for each process. In addition, NitrOS9 keeps an separate MMU table (DAT Image) for each process. So it is important to use the OS9 calls F$MapBlk and F$ClrBlk calls to map in memory blocks with the MMU.

When a new process is created, registers U, Y, DP and SP are set with U = start of data area, Y = end of data area, DP = page # of beginning page, SP = end of data area + 1.

Process Module Structure

There are 9 different types of modules in 4 possible languages:

Module Types				Language
Code	Module Type	Name		Code	Language
$1x	Program Module	Prgm		$x0	Data (non-executable)
$2x	Subroutine Module	Sbrtn		$x1	6809 Object Code
$3x	Multi-module	Multi		$x2	BASIC09 I-Code
$4x	Data Module	Data		$x3	PASCAL I-Code
$5x-$Bx	User-definable module			$x4-$xF	Reserved for Future Use
$Cx	OS9 System Module	Systm
$Dx	OS9 File Manager Module	FlMgr
$Ex	OS9 Device Driver Module	Drivr
$Fx	OS9 Device Descriptor Module	Devic

The two most used will be Program Modules and Data Modules.