MC68030 Datasheet, PDF (383/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
10.2.3.2.2 Not Ready Format Word. When the main processor initiates a cpSAVE
instruction by reading the save CIR the coprocessor can delay the save operation by
returning a not ready format word. The main processor then services any pending interrupts
and reads the save CIR again. The not ready format word delays the save operation until
the coprocessor is ready to save its internal state. The cpSAVE instruction can suspend
execution of a general or conditional coprocessor instruction; the coprocessor can resume
execution of the suspended instruction when the appropriate state is restored with a
cpRESTORE. If no further main processor services are required to complete coprocessor
instruction execution, it may be more efficient to complete the instruction and thus reduce
the size of the saved state. The coprocessor designer should consider the efficiency of
completing the instruction or of suspending and later resuming the instruction when the main
processor executes a cpSAVE instruction.
When the main processor initiates a cpRESTORE instruction by writing a format word to the
restore CIR, the coprocessor should usually terminate any current operations and restore
the state frame supplied by the main processor. Thus, the not ready format word should
usually not be returned by the coprocessor during the execution of a cpRESTORE
instruction. If the coprocessor must delay the cpRESTORE operation for any reason, it can
return the not ready format word when the main processor reads the restore CIR. If the main
processor reads the not ready format word from the restore CIR during the cpRESTORE
instruction, it reads the restore CIR again without servicing any pending interrupts.
10.2.3.2.3 Invalid Format Word. When the format word placed in the restore CIR to initiate
a cpRESTORE instruction does not describe a valid coprocessor state frame, the
coprocessor returns the invalid format word in the restore CIR. When the main processor
reads this format word during the cpRESTORE instruction, it writes the abort mask to the
control CIR and initiates format error exception processing. The two least significant bits of
the abort mask are 01; the fourteen most significant bits are undefined.
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MC68030 USER’S MANUAL
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