User`s manual

Using the Debugger
2-9
2
The System Call handler is accessible through the SC (system call)
instruction, with exception vector $00C00 (System Call Exception).
Refer to Chapter 5 for details on the routines available and how to
invoke them from within a user program.
Preserving the Operating Environment
This section explains how to avoid contaminating the operating
environment of the debugger. PPCBug uses some of the PowerPC
board onboard resources to contain temporary variables and
exception vectors. If the resources that PPCBug relies upon are
disturbed, PPCBug may not function reliably.
If your application enables translation through the Memory
Management Unit (MMU), and utilizes resources of the debugger
(e.g., system calls), your application must create the necessary
translation tables for the debugger to have access to its various
resources. The debugger honors the enabling of the MMU; it does
not alter or disable translation.
Memory Requirements
The debugger requires approximately 768KB (maybe less) of
read/write memory. The debugger will allocate this memory from
the top of memory. For example, on a system which contains 64
megabytes ($04000000) of read/write memory (i.e., DRAM), the
debugger's memory page will be located at $03F80000 to
$03FFFFFF.
This memory space is used by the debugger for program stack, I/O
buffers, variables, and register files. If an user program is loaded
(e.g., booted, S-Records) into memory, and if this program is
utilizing the debugger's programmatic interface (i.e., system calls),
the program must not modify this allocated memory.