MC68030 Datasheet, PDF (416/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
The MC68030 discards any instruction words that have been prefetched beyond the current
scanPC location when this primitive is issued with DR=1 (transfer to main processor). The
MC68030 then refills the instruction pipe from the scanPC address in the address space
indicated by the status register S bit.
If the MC68030 is operating in the trace on change of flow mode (T1:T0 in the status register
contains 01) when the coprocessor instruction begins to execute and if this primitive is
issued with DR=1 (from coprocessor to main processor), the MC68030 prepares to take a
trace exception. The trace exception occurs when the coprocessor signals that it has
completed all processing associated with the instruction. Changes in the trace modes due
to the transfer of the status register to main processor take effect on execution of the next
instruction.
10.4.18 Take Pre-Instruction Exception Primitive
The take pre-instruction exception primitive initiates exception processing using a
coprocessor-supplied exception vector number and the pre-instruction exception stack
frame format. This primitive applies to general and conditional category instructions. Figure
10-40 shows the format of the take pre-instruction exception primitive.
15
14 13 12 11 10
9
0
PC
0
1
1
1
0
8
7
0
0
VECTOR NUMBER
Figure 10-40. Take Pre-Instruction Exception Primitive Format
The primitive uses the PC bit as previously described. Bits [0-7] contain the exception vector
number used by the main processor to initiate exception processing.
When the main processor receives this primitive, it acknowledges the coprocessor
exception request by writing an exception acknowledge mask (refer to 10.3.2 Control CIR)
to the control CIR. The MC68030 then proceeds with exception processing as described in
8.1 Exception Processing Sequence. The vector number for the exception is taken from
bits [0-7] of the primitive, and the MC68030 uses the four-word stack frame format shown in
Figure 10-41.
10-56
MC68030 USER’S MANUAL
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