Motorola MC68030 User Manual page 414

-
10-26
MAIN PROCESSOR
Ml RECOGNIZE COPROCESSOR INSTRUCTION F-liNE
OPERATION WORD
M2 READ SAVE CIR TO INITIATE THE cpSAVE INSTRUCTION
M3 IF (FORMAT
=
NOT READYI DO STEPS 11 AND 21 BELOW . . . -
11 SERVICE PENDING INTERRUPTS
21 GO TO M2
M3 EVALUATE EFFECTIVE AODRESS SPECIFIED IN F-liNE
OPWORD AND STORE FORMAT WORD AT
EFFECTIVE ADDRESS
M4 IF (FORMAT
=
EMPTYI GO TO M5
ELSE. TRANSFER NUMBER OF BYTES INDICATED
IN FORMAT WORD FROM OPERAND CIR TO
EFFECTIVE ADDRESS
M5 PROCEED WITH EXECUTION OF NEXT INSTRUCTION
COPROCESSOR
Cl IF (NOT READY TO BEGIN CONTEXT SAVE OPERATIDNI
DO STEPS 11 AND 21 BELOW
11
PLACE NOT READY FORMAT CODE IN SAVE CIR
21 SUSPEND DR COMPLETE CURRENT OPERATIONS
C2 PLACE APPROPRIATE FORMAT WORD IN SAVE CIR
C3 TRANSFER NUMBER OF BYTES INDICATED IN
FORMAT WORD THROUGH OPERAND CIR
Figure 10-16. Coprocessor Context Save
In~truction
Protocol
to be transferred from the coprocessor to the effective address specified. If
the state information is not a multiple of four bytes in size, the MC68030
initiates format error exception processing (refer to 10.5.1.5 FORMAT ER-
RORS). The coprocessor and main processor coordinate the transfer of the
internal state of the coprocessor using the operand CIR. The MC68030 com-
pletes the coprocessor context save by repeatedly reading the operand CIR
and writing the information obtained into memory until all the bytes specified
in the coprocessor format word have been transferred. Following a cpSAVE
instruction, the coprocessor should be in an idle state -that is, not executing
any coprocessor instructions.
The cpSAVE instruction is a privileged instruction. When the main processor
identifies a cpSAVE instruction, it checks the supervisor bit in the status
register to determine whether it is operating at the supervisor privilege level.
If the MC68030 attempts to execute a cpSAVE instruction while at the user
privilege level (status register bit [13]
=
0), it initiates privilege violation ex-
ception processing without accessing any of the coprocessor interface reg-
isters (refer to 10.5.2.3 PRIVILEGE VIOLATIONS).
The MC68030 initiates format error exception processing if it reads an invalid
format word (or a valid format word whose length field is not a multiple of
four bytes) from the save CIR during the execution of a cpSAVE instruction
(refer to 10.2.3.2.3 Invalid Format Word). The MC68030 writes an abort mask
(refer to 10.2.3.2.3 Invalid Format Word) to the control CIR to abort the co-
processor instruction prior to beginning exception processing. Figure 10-16
MC68030 USER'S MANUAL
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