CPU32BUG

Table of Contents

This section will give you a high level overview of the use of the CPU32BUG debugging monitor on the MRM board. For a complete description refer to the Motorola M68CPU32BUG DEBUG MONITOR USER'S MANUAL (M68CPU32BUG/D); maybe available here.

To make the MRM more readily usable, it comes preloaded with the a debugging monitor program in ROM, referred to as CPU32BUG. This program, once connected to the terminal emulator and power applied boots a modified version of Motorola's CPU32BUG in the debugging mode (CPU32BUG> prompt). Here, it has been set so you can erase flash memory (EF), load program (LO), and lots of others things which are beyond this documents scope. Obviously, in terms of memory, the program isn't free--it cost on-board address space; in short, about 64K in ROM and 12K in RAM (Ref. MRM Addressing). It is the makefile in combination with the linker script which links in the cpu32bug.o (cpu32bug.S supplied with MRM CD-ROM) module which sets up a symbolic link to the CPU32BUG TRAP #15 and the _exit external program symbol as follows:

SYM (_exit):
	link	fp, IMM(0)
        trap	IMM(15)
        .word	RETURN

TRAP #15 transfers control back to CPU32Bug at the end of a user program (refer to the .RETURN function, paragraph 5.2.16 CPU32DEBUG User's manual).

Mark's modified commands:

• LO: Load S-Record - Loads S-Record files normally. However, when loading files to the internal Flash, LO handles all Flash write setup and in addition, will not allow writes to sector 0 containing the CPU32BUG.

• EF: Erase Flash - Erases sectors 1-7 (Memory locations 0x90000-0xFFFFF). Sector 0 which contains the modified CPU32BUG is not erased.