ARM Processor Instruction Set

ARM Processor Instruction Set
5.12 Coprocessor data operations (CDP)
Use of the CDP instruction on the ARM processor will cause an undefined instruction
trap to be taken, which may be used to emulate the coprocessor instruction.
The instruction is only executed if the condition is true. The various conditions are
defined at the beginning of this chapter. The instruction encoding is shown in ➲Figure
5-23: Coprocessor data operation instruction.
This class of instruction is used to tell a coprocessor to perform some internal
operation. No result is communicated back to the processor, 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 the processor to perform independent tasks in parallel.
31 28 27 24 23
20
19
16
15
12
11
8
7
5 4 3
0
Cond
1110 CP Opc CRn CRd CP# CP 0 CRm
Preliminary - Unrestricted
5.12.1 The coprocessor fields
Coprocessor operand register
Coprocessor information
Coprocessor number
Coprocessor destination register
Coprocessor operand register
Coprocessor operation code
Condition field
Figure 5-23: Coprocessor data operation instruction
Only bit 4 and bits 24 to 31 are significant to the processor; 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.
5.12.2 Instruction cycle times
All CDP instructions are emulated in software: the number of cycles taken will depend
on the coprocessor support software.
5-42
ARM7500 Data Sheet
ARM DDI 0050C