MC68030 Datasheet, PDF (431/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
10.5.2.6 INTERRUPTS. Interrupt processing, discussed in 8.1.9 Interrupt Exceptions, can
occur at any instruction boundary. Interrupts are also serviced during the execution of a
general or conditional category instruction under either of two conditions. If the main
processor reads a null primitive with CA=1 and IA=1, it services any pending interrupts prior
to reading the response CIR. Similarly, if a trace exception is pending during cpGEN
instruction execution and the main processor reads a null primitive with CA=0, IA=1, and
PF=0 (refer to 10.5.2.5 Trace Exceptions), the main processor services pending interrupts
prior to reading the response CIR again.
The MC68030 uses the ten-word mid-instruction stack frame when it services interrupts
during the execution of a general or conditional category coprocessor instruction. Since it
uses this stack frame, the main processor can perform all necessary processing and then
return to read the response CIR. Thus, it can continue the coprocessor instruction during
which the interrupt exception was taken.
The MC68030 also services interrupts if it reads the not ready format word from the save
CIR during a cpSAVE instruction. The MC68030 uses the normal four word pre-instruction
stack frame when it services interrupts after reading the not ready format word. Thus, the
processor can service any pending interrupts and execute an RTE to return and re-initiate
the cpSAVE instruction by reading the save CIR.
10.5.2.7 FORMAT ERRORS . The MC68030 can detect a format error while executing a
cpSAVE or cpRESTORE instruction if the length field of a valid format word is not a multiple
of four bytes in length. If the MC68030 reads a format word with an invalid length field from
the save CIR during the cpSAVE instruction, it aborts the coprocessor instruction by writing
an abort mask (refer to 10.3.2 Control CIR) to the control CIR and initiates format error
exception processing. If the MC68030 reads a format word with an invalid length field from
the effective address specified in the cpRESTORE instruction, the MC68030 writes that
format word to the restore CIR and then reads the coprocessor response from the restore
CIR. The MC68030 then aborts the cpRESTORE instruction by writing an abort mask (refer
to 10.3.2 Control CIR) to the control CIR and initiates format error exception processing.
The MC68030 uses the four-word pre-instruction stack frame and the format error vector
number 14 when it initiates format error exception processing. Thus, if the exception handler
does not modify the stack frame, the main processor attempts to restart the instruction
during which the exception occurred after it executes an RTE to return from the handler.
MOTOROLA
MC68030 USER’S MANUAL
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