D8.21 TRCDEVAFF0, Device Affinity Register 0

The TRCDEVAFF0 provides an additional core identification mechanism for scheduling purposes in a cluster. TRCDEVAFF0 is a read-only copy of MPIDR accessible from the external debug interface.

Bit field descriptions

The TRCDEVAFF0 is a 32-bit register.

Figure D8-20 TRCDEVAFF0 bit assignments
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RES1, [31]
U, [30]

Indicates a single core system, as distinct from core 0 in a cluster. This value is:

0Core is part of a multiprocessor system. This is the value for implementations with more than one core, and for implementations with an ACE or CHI master interface.
1Core is part of a uniprocessor system. This is the value for single core implementations with an AXI master interface.
RES0, [29:25]
MT, [24]

Indicates whether the lowest level of affinity consists of logical cores that are implemented using a multithreading type approach. This value is:

0Performance of cores at the lowest affinity level is largely independent.
Aff2, [23:16]

Affinity level 2. Second highest level affinity field.

Indicates the value read in the CLUSTERIDAFF2 configuration signal.

Aff1, [15:8]

Affinity level 1. Third highest level affinity field.

Indicates the value read in the CLUSTERIDAFF1 configuration signal.

Aff0, [7:0]

Affinity level 0. Lowest level affinity field.

Indicates the core number in the Cortex®-A55 core. The possible values are:

0x0A cluster with one core only.
0x0, 0x1A cluster with two cores.
0x0, 0x1, 0x2A cluster with three cores.
0x0, 0x1, 0x2, 0x3A cluster with four cores.

Bit fields and details not provided in this description are architecturally defined. See the Arm® Architecture Reference Manual Armv8, for Armv8-A architecture profile.

The TRCDEVAFF0 can be accessed through the external debug interface, offset 0xFA8.

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