4.2.5. Multiprocessor Affinity Register

The MPIDR characteristics are:


To identify:

  • whether the processor is part of a Cortex-A9 MPCore implementation.

  • Cortex-A9 processor accesses within a Cortex-A9 MPCore processor

  • the target Cortex-A9 processor in a multi-processor cluster system.

Usage constraints

The MPIDR is:

  • only accessible in privileged mode.

  • common to the Secure and Non-secure states.


Available in all configurations. The value of the U bit, bit [30], indicates if the configuration is a multiprocessor configuration or a uniprocessor configuration.


See the register summary in Table 4.1.

Figure 4.2 shows the MPIDR bit assignments.

Figure 4.2. MPIDR bit assignments

Table 4.3 shows the MPIDR bit assignments.

Table 4.3. MPIDR bit assignments

[31]-Indicates the register uses the new multiprocessor format. This is always 1.
[30]U bit

0 = Processor is part of a multiprocessor system.

1 = Processor is part of a uniprocessor system.

[11:8]Cluster ID

Value read in CLUSTERID configuration pins. It identifies a Cortex-A9 MPCore processor in a system with more than one Cortex-A9 MPCore processor present. SBZ in a uniprocessor configuration.

[1:0]CPU ID

The value depends on the number of configured processors.

  • One Cortex-A9 processor, the CPU ID is 0x0.

  • Two Cortex-A9 processors, the CPU IDs are 0x0 and 0x1.

  • Three Cortex-A9 processors, the CPU IDs are 0x0, 0x1, and 0x2.

  • Four Cortex-A9 processors, the CPU IDs are 0x0, 0x1, 0x2,and 0x3.

To access the MPIDR, use:

MRC p15,0,<Rd>,c0,c0,5; read Multiprocessor ID register
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