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ID_DFR1, Debug Feature Register 1

The ID_DFR1 characteristics are:

Purpose

Provides top level information about the debug system in AArch32.

For general information about the interpretation of the ID registers, see 'Principles of the ID scheme for fields in ID registers'.

Configuration

AArch32 System register ID_DFR1 bits [31:0] are architecturally mapped to AArch64 System register ID_DFR1_EL1[31:0] .

This register is present only when AArch32 is supported at any Exception level. Otherwise, direct accesses to ID_DFR1 are UNDEFINED.

Note

Prior to the introduction of the features described by this register, this register was unnamed and reserved, RES0 from EL1, EL2, and EL3.

Attributes

ID_DFR1 is a 32-bit register.

Field descriptions

The ID_DFR1 bit assignments are:

313029282726252423222120191817161514131211109876543210
RES0MTPMU

Bits [31:4]

Reserved, RES0.

MTPMU, bits [3:0]

Multi-threaded PMU extension. Defined values are:

MTPMUMeaning
0b0000

FEAT_MTPMU not implemented. If FEAT_PMUv3 is implemented, it is IMPLEMENTATION DEFINED whether PMEVTYPER<n>.MT are read/write or RES0.

0b0001

FEAT_MTPMU and FEAT_PMUv3 implemented. PMEVTYPER<n>.MT are read/write. When FEAT_MTPMU is disabled, the Effective values of PMEVTYPER<n>.MT are 0.

0b1111

FEAT_MTPMU not implemented. If FEAT_PMUv3 is implemented, PMEVTYPER<n>.MT are RES0.

All other values are reserved.

FEAT_MTPMU implements the functionality identified by the value 0b0001.

From Armv8.6, in an implementation that includes FEAT_PMUv3, the value 0b0000 is not permitted.

In an implementation that does not include FEAT_PMUv3, the value 0b0001 is not permitted.

Accessing the ID_DFR1

Accesses to this register use the following encodings:

MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>}

coprocopc1CRnCRmopc2
0b11110b0000b00000b00110b101
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) && (!IsZero(ID_DFR1) || boolean IMPLEMENTATION_DEFINED "ID_DFR1 trapped by HCR_EL2.TID3") && HCR_EL2.TID3 == '1' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x03);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && (!IsZero(ID_DFR1) || boolean IMPLEMENTATION_DEFINED "ID_DFR1 trapped by HCR.TID3") && HCR.TID3 == '1' then
        AArch32.TakeHypTrapException(0x03);
    else
        return ID_DFR1;
elsif PSTATE.EL == EL2 then
    return ID_DFR1;
elsif PSTATE.EL == EL3 then
    return ID_DFR1;