MC68030 Datasheet, PDF (420/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
10.4.20 Take Post-Instruction Exception Primitive
The take post-instruction exception primitive initiates exception processing using a
coprocessor-supplied exception vector number and the post-instruction exception stack
frame format. This primitive applies to general and conditional category instructions. Figure
10-44 shows the format of the take post-instruction exception primitive.
15
14 13 12 11 10
9
0
PC
0
1
1
1
1
8
7
0
0
VECTOR NUMBER
Figure 10-44. Take Post-Instruction Exception Primitive Format
This 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 performs 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 six-word stack frame format shown in
Figure 10-45.
The value in the main processor scanPC at the time this primitive is received is saved in the
scanPC field of the post-instruction exception stack frame. The value of the program counter
saved is the F-line operation word address of the coprocessor instruction during which the
primitive is received.
(UNABLE TO LOCATE ART)
Figure 10-45. MC68030 Post-Instruction Stack Frame
When the MC68030 receives the take post-instruction exception primitive, it assumes that
the coprocessor either completed or aborted the instruction with an exception. If the
exception handler does not modify the stack frame, the MC68030 returns from the exception
handler to begin execution at the location specified by the scanPC field of the stack frame.
This location should be the address of the next instruction to be executed.
The coprocessor uses this primitive to request exception processing when it completes or
aborts an instruction while the main processor is awaiting a normal response. For a general
category instruction, the response is a release; for a conditional category instruction, it is an
evaluated true/false condition indicator. Thus, the operation of the MC68030 in response to
this primitive is compatible with standard M68000 Family instruction related exception
processing (for example, the divide-by-zero exception).
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MC68030 USER’S MANUAL
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