MPIDR, Multiprocessor Affinity Register

The MPIDR characteristics are:

Purpose

In a multiprocessor system, provides an additional PE identification mechanism for scheduling purposes.

Configuration

AArch32 System register MPIDR bits [31:0] are architecturally mapped to AArch64 System register MPIDR_EL1[31:0] .

In a uniprocessor system Arm recommends that each Aff<n> field of this register returns a value of 0.

Attributes

MPIDR is a 32-bit register.

Field descriptions

The MPIDR bit assignments are:

M, bit [31]

Indicates whether this implementation includes the functionality introduced by the ARMv7 Multiprocessing Extensions. The possible values of this bit are:

In Armv8, this bit is RAO.

U, bit [30]

Indicates a Uniprocessor system, as distinct from PE 0 in a multiprocessor system. The possible values of this bit are:

Bits [29:25]

Reserved, RES0.

MT, bit [24]

Indicates whether the lowest level of affinity consists of logical PEs that are implemented using a multithreading type approach. See the description of Aff0 for more information about affinity levels. The possible values of this bit are:

Aff2, bits [23:16]

Affinity level 2. See the description of Aff0 for more information.

Aff1, bits [15:8]

Affinity level 1. See the description of Aff0 for more information.

Aff0, bits [7:0]

Affinity level 0. This is the affinity level that is most significant for determining PE behavior. Higher affinity levels are increasingly less significant in determining PE behavior. The assigned value of the MPIDR.{Aff2, Aff1, Aff0} or MPIDR_EL1.{Aff3, Aff2, Aff1, Aff0} set of fields of each PE must be unique within the system as a whole.

if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HSTR_EL2.T0 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HSTR.T0 == '1' then
        AArch32.TakeHypTrapException(0x03);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) then
        return VMPIDR_EL2<31:0>;
    elsif EL2Enabled() && ELUsingAArch32(EL2) then
        return VMPIDR;
    else
        return MPIDR;
elsif PSTATE.EL == EL2 then
    return MPIDR;
elsif PSTATE.EL == EL3 then
    return MPIDR;