Motorola MC68030 User Manual page 401

Figure 10-8 shows the protocol for a conditional category coprocessor in-
struction. The main processor initiates execution of an instruction in this
category by writing a condition selector to the condition CIR. The coprocessor
decodes the condition selector to determine the condition to evaluate. The
coprocessor can use response primitives to request that the main processor
provide services required for the condition evaluation. After evaluating the
condition, the coprocessor returns a true/false indicator to the main processor
by placing a null primitive (refer to 10.4.4 Null Primitive) in the response CIR.
The main processor completes the coprocessor instruction execution when
it receives the condition indicator from the coprocessor.
MAIN PROCESSOR
Ml RECOGNIZE COPROCESSOR INSTRUCTION F·lINE
OPERATION WORD
M2 WRITE COPROCESSOR CONOITION SELECTOR TO
CONDITION CIR
M3 READ COPROCESSOR RESPONSE PRIMITIVE CODE
FRDM RESPONSE CIR
1) PERFORM SERVICE REQUESTED BY RESPONSE
PRIMITIVE
2) IF (COPROCESSOR RESPONSE PRIMITIVE
- .
Cl
C2
~
C3
COPRDCESSOR
DECODE CONDITION SELECTOR AND INITIATE
CDNDITION EVALUATION
WHILE (MAIN PROCESSOR SERVICE IS REQUIRED
DO STEPS 1) ANO 2) BELOW
1) REOUEST SERVICE BY PLACING APPROPRIATE
RESPONSE PRIMITIVE CODE IN RESPONSE CIR
2) RECEIVE SERVICE FROM MAIN PROCESSOR
COMPLETE CONDITION EVALUATION
INDICATES "COME AGAIN") GO TO M3
(SEE NOTE 1)
C4 REFLECT "NO COME AGAIN" STATUS WITH TRUE/FALSE
CONDITION INDICATOR IN RESPONSE CIR
M4
COMPLETE EXECUTION OF INSTRUCTION BASED ON
THE TRUE/FALSE CONDITION INDICATOR
RETURNED IN THE RESPONSE CIR
NOTES: 1. All coprocessor response primitives, except the Null primitive, that allow the "Come Again"
primitive attribute must indicate "Come Again" when used during the execution of a
conditional category instruction. If a "Come Again" attribute is not indicated in one of these
primitives, the main processor will initiate protocol violation exception processing (see 10.6.2.1
PROTOCOL VIOLATIONS)
Figure 10-8. Coprocessor Interface Protocol for Conditional
Category Instructions
10.2.2.1 BRANCH ON COPROCESSOR CONDITION INSTRUCTION. The condi-
tional instruction category includes two formats ofthe M68000 Family branch
instruction. These instructions branch on conditions related to the copro-
cessor operation. They execute similarly to the conditional branch instruc-
tions provided in the M68000 Family instruction set.
MOTOROLA MC68030 USER'S MANUAL
10-13
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