Motorola MC68030 User Manual page 399

An instruction in the coprocessor general instruction category optionally
includes a number of extension words following the coprocessor command
word. These words can provide additional information required for the co-
processor instruction. For example, if the coprocessor requests that the
MC68030 calculate an effective address during coprocessor instruction ex-
ecution, information required for the calculation must be included in the
instruction format as effective address extension words.
10.2.1.2 PROTOCOL. The execution of a cpGEN instruction follows the protocol
shown in Figure 10-7. The main processor initiates communication with the
coprocessor by writing the instruction command word to the command CIA.
The coprocessor decodes the command word to begin processing the cpGEN
instruction. Coprocessor design determines the interpretation of the copro-
cessor command word; the MC68030 does not attempt to decode it.
MOTOROLA
MAIN PROCESSOR
Ml RECOGNIZE COPROCESSOR INSTRUCTION F-UNE
OPERATION WORD
M2 WRITE COPROCESSOR COMMAND WORD TO
COMMAND CIR
M3 READ COPROCESSOR RESPONSE PRIMITIVE
CODE FROM RESPONSE CIR
1) PERFORM SERVICE REQUESTED BY RESPONSE
PRIMITIVE
2) IF (COPROCESSOR RESPONSE PRIMITIVE
INDICATES "COME AGAIN") GO TO M3
(SEE NOTE 1)
M4 PROCEED WITH EXECUTION OF NEXT INSTRUCTION
(SEE NOTE 2)
COPROCESSOR
---.. Cl DECODE COMMAND WORD AND INITIATE
COMMAND EXECUTION
C2
WHILE (MAIN PROCESSOR SERVICE IS REQUIRED)
DO STEPS 1) AND 2) BELOW
~
1) REQUEST SERVICE BY PLACING APPROPRIATE
RESPONSE PRIMITIVE CODE IN RESPONSE CIR
2) RECEIVE SERVICE FROM MAIN PROCESSOR
C3
REFLECT "NO COME AGAIN" IN RESPONSE CIR
C4 COMPLETE COMMAND EXECUTION
C5 REFLECT "PROCESSING FINISHED" STATUS IN
RESPONSE CIR
NOTES: 1. "Come Again" indicates that further service of the main processor is being requested
by the coprocessor
2. The next instruction should be the operation word pointed to by the ScanPC at this point.
The operation of the MC68030 ScanPC is discussed in 10.4.1 ScanPC
Figure 10-7. Coprocessor Interface Protocol for
General Category Instructions
MC68030 USER'S MANUAL
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