Coprocessor Data Operations (CDP)

The instruction is only executed if the condition is true. The various conditions are defined in Table 6. The instruction encoding is shown in Figure 34.

This class of instruction is used to tell a coprocessor to perform some internal operation. No result is communicated

Figure 34. Coprocessor Data Operation Instruction

back to ARM7TDMI, and it will not wait for the operation to complete. The coprocessor could contain a queue of such instructions awaiting execution, and their execution can overlap other activity, allowing the coprocessor and ARM7TDMI to perform independent tasks in parallel.

The coprocessor fields

Only bit 4 and bits 24 to 31 are significant to ARM7TDMI. The remaining bits are used by coprocessors. The above field names are used by convention, and particular coprocessors may redefine the use of all fields except CP# as appropriate. The CP# field is used to contain an identifying number (in the range 0 to 15) for each coprocessor, and a coprocessor will ignore any instruction which does not contain its number in the CP# field.

The conventional interpretation of the instruction is that the coprocessor should perform an operation specified in the CP Opc field (and possibly in the CP field) on the contents of CRn and CRm, and place the result in CRd.

Instruction cycle times

Coprocessor data operations take 1S + bI incremental cycles to execute, where b is the number of cycles spent in the coprocessor busy-wait loop.

Coprocessor operand register

Coprocessor information

Coprocessor number

Coprocessor destination register

Coprocessor operand register

Coprocessor operation code

Condition field

S and I are as defined in Cycle Types.

Assembler syntax

CDP{cond}

p#,<expression1>,cd,cn,cm{,<expression2>}

{cond} two character condition mnemonic. See Table 6.

p# the unique number of the required coprocessor

<expression1> evaluated to a constant and placed in the CP Opc field

cd, cn and cm evaluate to the valid coprocessor register numbers CRd, CRn and CRm respectively

<expression2> where present is evaluated to a constant and placed in the CP field

Examples

Instruction Set

67