ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Instruction Synchronization Barrier operation
Protected Memory System Architecture (PMSA)
In ARMv7, the ISB instruction is used to perform an Instruction Synchronization Barrier, see ISB on
page A8-102.
The deprecated CP15 c7 encoding for an Instruction Synchronization Barrier is set to 0, set to
c7, set to c5, and set to 4.
Data Synchronization Barrier operation
In ARMv7, the DSB instruction is used to perform a Data Synchronization Barrier, see DSB on page A8-92.
The deprecated CP15 c7 encoding for a Data Synchronization Barrier is set to 0, set to c7,
set to c10, and set to 4. This operation performs the full system barrier performed by the DSB
instruction.
Data Memory Barrier operation
In ARMv7, the DMB instruction is used to perform a Data Memory Barrier, see DMB on page A8-90.
The deprecated CP15 c7 encoding for a Data Memory Barrier is set to 0, set to c7, set to
c10, and set to 5. This operation performs the full system barrier performed by the DMB instruction.
CP15 c7, No Operation (NOP)
ARMv6 includes two CP15 c7 operations that are not supported in ARMv7, with encodings that become
No Operation (NOP) in ARMv7. These are:
The Wait For Interrupt (CP15WFI) operation. In ARMv7 this operation is performed by the WFI
instruction, that is available in the ARM and Thumb instruction sets. For more information, see WFI
on page A8-810.
The prefetch instruction by MVA operation. In ARMv7 this operation is replaced by the PLI
instruction, that is available in the ARM and Thumb instruction sets. For more information, see PLI
(immediate, literal) on page A8-242, and PLI (register) on page A8-244.
In ARMv7, the CP15 c7 encodings that were used for these operations must be valid write-only operations
that perform a NOP. These encodings are:
for the ARMv6 CP15WFI operation:
— set to 0, set to c7, set to c0, and set to 4
for the ARMv6 prefetch instruction by MVA operation:
— set to 0, set to c7, set to c13, and set to 1.
B4.6.28 CP15 c8, Not used on a PMSA implementation
CP15 c8 is not used on an ARMv7-R implementation, see Unallocated CP15 encodings on page B4-27.
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