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. In addition, NitrOS9 keeps an separate MMU table 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.

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