Motorola MVME187 manual Comparison with M68000-Based Firmware, 187Bug Implementation

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Debugger General Information

Comparison with M68000-Based Firmware

If you have used one or more of Motorola's other debugging packages, you will find the RISC 187Bug very similar, after making due allowances for the architectural differences between the M68000 and M88000 CPU architectures. These differences are primarily reflected as follows:

❏Instruction mnemonics and addressing modes of the assembler/disassembler differ somewhat in 187Bug.

❏187Bug uses registers instead of the stack for the passing of arguments to or from the TRAP #496 handler.

❏The interactive commands in 187Bug are more consistent. For example, delimiters between commands and arguments may now be commas or spaces interchangeably.

187Bug Implementation

MVME187Bug is written largely in the ÒCÓ programming language, providing benefits of portability and maintainability. Where necessary, assembler has been used in the form of separately compiled modules containing only assembler code; no mixed language modules are used.

Physically, 187Bug is contained in two of the four 44-pin PLCC/CLCC EPROMs, providing 512KB (128K words) of storage. Both EPROMs are necessary regardless of how much space is actually occupied by the firmware, because of the 32-bit word- oriented M88000 memory bus architecture.

The executable code is checksummed at every power-on or reset firmware entry, and the result (which includes a pre-calculated checksum contained in the EPROMs), is tested for an expected zero. Thus, users are cautioned against modification of the EPROMs unless re-checksum precautions are taken.

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