Motorola MVME1603, Installation And Use Manual, Page: 150 / 222

Overview
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Because PPCBug is command-driven, it performs its various operations in
response to user commands entered at the keyboard. The flow of control in
PPCBug is described in the PPCBug Firmware Package User’s Manual.
When you enter a command, PPCBug executes the command and the
prompt reappears. However, if you enter a command that causes execution
of user target code (e.g., GO), then control may or may not return to
PPCBug, depending on the outcome of the user program.
The PPCBug is similar to previous Motorola firmware debugging
packages (e.g., MVME147Bug, MVME167Bug, MVME187Bug), with
differences due to microprocessor architectures. These are primarily
reflected in the instruction mnemonics, register displays, addressing
modes of the assembler/disassembler, and the passing of arguments to the
system calls.
Memory Requirements
PPCBug requires a total of 512KB of read/write memory (i.e., DRAM).
The debugger allocates this space from the top of memory. For example, a
system containing 64MB ($04000000) of read/write memory will place
the PPCBug memory page at locations $03F80000 to $03FFFFFF.
PPCBug Implementation
PPCBug is written largely in the C programming language, providing
benefits of portability and maintainability. Where necessary, assembly
language has been used in the form of separately compiled program
modules containing only assembler code. No mixed-language modules are
used.
Physically, PPCBug is contained in two socketed 32-pin PLCC/CLCC
FLASH devices that together provide 1MB of storage. The executable
code is checksummed at every power-on or reset firmware entry, and the
result (which includes a precalculated checksum contained in the FLASH
devices), is tested for an expected zero.