MC68030 Datasheet, PDF (280/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Exception Processing
ENTRY
TEMP (SP) +
READ FORMAT WORD
SR TEMP
SP SP + 6
INVALID FORMAT WORD
TAKE FORMAT
ERROR EXCEPTION
OTHERWISE
FORMAT CODE = $1
(THROWAWAY FRAME)
OTHERWISE
FORMAT CODE = $0 (4-WORD FRAME)
OTHER FORMATS
PC (SP) +
SP SP + 6
SR TEMP
EXIT
Figure 8-8. RTE Instruction for Throwaway Four-Word Frame
If a format error or bus error exception occurs during the frame validation sequence of the
RTE instruction, either due to any of the errors previously described or due to an illegal
format code, the processor creates a normal four-word or a bus fault stack frame below the
frame that it was attempting to use. In this way, the faulty stack frame remains intact. The
exception handler can examine or repair the faulty frame. In a multiprocessor system, the
faulty frame can be left to be used by another processor of a different type (e.g., an
MC68010, MC68020, or a future M68000 processor) when appropriate.
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MC68030 USER’S MANUAL
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