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Compiling Programs for the Debugger
Writing programs for simulation
Several microprocessor features work differently in the simulator:
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68020 Module Support — CALLM and RTM
CALLM and RTM are used in conjunction with external hardware to
maintain a finer resolution of access control than that afforded by the
supervisor and master bits.
On the actual 68020 microprocessor, if the module descriptor used by a
CALLM or RTM instruction has type $01, the 68020 will perform a CPU
space read from address $10004 to determine the legality of an access level
change. The resulting status value must be between 1 and 7 inclusive or a
format exception will occur.
The simulated CALLM and RTM instructions do not perform a CPU space
read. They interrogate the simulator access level status variable @as, which is
initially 1 (valid status). You can change @as via the Memory Register
command, for example:
Memory Register @as = 4
72
Some instructions and exception conditions cause the microprocessor to
read or write data to CPU space. CPU space references are intended for
communication with external hardware (such as a floating point
coprocessor or security-checking device). For this reason, the memory
simulator ignores CPU space writes and returns $FF for CPU space reads.
Thus, there is no mechanism for simulating coprocessor communication.
Since the debugger provides complete step and breakpoint control, the
trace bits in the Status Register are ignored; they do not cause a trace
exception to occur after each instruction.
The TRAP instruction causes an illegal instruction exception. Use normal
debugger commands to set breakpoints.
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