Supervisor Check Primitive; Transfer Operation Word Primitive - Motorola MC68020 User Manual

7.4.5 Supervisor Check Primitive

The supervisor check primitive verifies that the main processor is operating in the
supervisor privilege level while executing a coprocessor instruction. This primitive applies
to instructions in the general and conditional coprocessor instruction categories. Figure
7-25 shows the format of the supervisor check primitive.
15 14 13
1 PC
The supervisor check primitive uses the PC bit as described in 7.4.2 Coprocessor
Response Primitive General Format. Bit 15 is shown as one, but during execution of a
general category instruction, this primitive performs the same operations, regardless of the
value of bit 15. However, if this primitive is issued with bit 15 = 0 during a conditional
category instruction, the main processor initiates protocol violation exception processing.
When the MC68020/EC020 reads the supervisor check primitive from the response CIR, it
checks the value of the S-bit in the SR. If S = 0 (main processor operating at user privilege
level), the main processor aborts the coprocessor instruction by writing an abort mask to
the control CIR (refer to 7.3.2 Control CIR). The main processor then initiates privilege
violation exception processing (refer to 7.5.2.3 Privilege Violations). If the main
processor is at the supervisor privilege level when it receives this primitive, it reads the
response CIR again.
The supervisor check primitive allows privileged instructions to be defined in the
coprocessor general and conditional instruction categories. This primitive should be the
first one issued by the coprocessor during the dialog for an instruction that is implemented
as privileged.

7.4.6 Transfer Operation Word Primitive

The transfer operation word primitive requests a copy of the coprocessor instruction
operation word for the coprocessor. This primitive applies to general and conditional
category instructions. Figure 7-26 shows the format of the transfer operation word
primitive.
15 14 13
CA PC
Figure 7-26. Transfer Operation Word Primitive Format
7-34
12 11 10 9
0 0 0 1 0
Figure 7-25. Supervisor Check Primitive Format
12 11 10 9
0 0 0 1 1
M68020 USER'S MANUAL
8 7 6 5 4
0 0 0 0 0
8 7 6 5 4
1 0 0 0 0
3 2 1 0
0 0 0 0
3 2 1 0
0 0 0 0
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