MC68030 Datasheet, PDF (265/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Exception Processing
Exception processing for illegal and unimplemented instructions is similar to that for
instruction traps. When the processor has identified an illegal or unimplemented instruction,
it initiates exception processing instead of attempting to execute the instruction. The
processor copies the status register, enters the supervisor privilege level, and clears the
trace bits, disabling further tracing. The processor generates the vector number, either 4,
10, or 11, according to the exception type. The illegal or unimplemented instruction vector
offset, current program counter, and copy of the status register are saved on the supervisor
stack, with the saved value of the program counter being the address of the illegal or
unimplemented instruction. Instruction execution resumes at the address contained in the
exception vector. It is the responsibility of the handling routine to adjust the stacked program
counter if the instruction is emulated in software or is to be skipped on return from the
handler.
8.1.6 Privilege Violation Exception
To provide system security, the following instructions are privileged:
ANDI TO SR
EOR to SR
cpRESTORE
cpSAVE
MOVE from SR
MOVE to SR
MOVE USP
MOVEC
MOVES
ORI to SR
PFLUSH
PLOAD
PMOVE
PTEST
RESET
RTE
STOP
An attempt to execute one of the privileged instructions while at the user privilege level
causes a privilege violation exception. Also, a privilege violation exception occurs if a
coprocessor requests a privilege check and the processor is at the user level.
MOTOROLA
MC68030 USER’S MANUAL
8-11