ID_DFR0 Debug Feature Register 0 when FEAT_AA32EL1 is implemented ID_DFR0_EL1 Architectural AArch64 31 0 31 0 31 0 31 0 Provides top-level information about the debug system in AArch32 state. Must be interpreted with the Main ID Register, MIDR. For general information about the interpretation of the ID registers see 'Principles of the ID scheme for fields in ID registers'. Identification Registers ID_DFR0 is a 32-bit register. TraceFilt 31 28 31:28 Armv8.4 Self-hosted Trace Extension version. All other values are reserved. FEAT_TRF implements the functionality identified by the value 0b0001. From Armv8.4, if FEAT_ETMv4 is implemented, the value 0b0000 is not permitted. If FEAT_ETE is implemented, the value 0b0000 is not permitted. 0b0000 Armv8.4 Self-hosted Trace Extension not implemented. 0b0001 Armv8.4 Self-hosted Trace Extension implemented. RO PerfMon 27 24 27:24 Performance Monitors Extension version. This field does not follow the standard ID scheme, but uses the alternative ID scheme described in 'Alternative ID scheme used for the Performance Monitors Extension version'. All other values are reserved. FEAT_PMUv3 implements the functionality identified by the value 0b0011. FEAT_PMUv3p1 implements the functionality identified by the value 0b0100. FEAT_PMUv3p4 implements the functionality identified by the value 0b0101. FEAT_PMUv3p5 implements the functionality identified by the value 0b0110. FEAT_PMUv3p7 implements the functionality identified by the value 0b0111. FEAT_PMUv3p8 implements the functionality identified by the value 0b1000. FEAT_PMUv3p9 implements the functionality identified by the value 0b1001. In any Armv8 implementation, the values 0b0001 and 0b0010 are not permitted. From Armv8.1, if FEAT_PMUv3 is implemented, the value 0b0011 is not permitted. From Armv8.4, if FEAT_PMUv3 is implemented, the value 0b0100 is not permitted. From Armv8.5, if FEAT_PMUv3 is implemented, the value 0b0101 is not permitted. From Armv8.7, if FEAT_PMUv3 is implemented, the value 0b0110 is not permitted. From Armv8.8, if FEAT_PMUv3 is implemented, the value 0b0111 is not permitted. From Armv8.9, if FEAT_PMUv3 is implemented, the value 0b1000 is not permitted. In Armv7, the value 0b0000 can mean that PMUv1 is implemented. PMUv1 and PMUv2 are not permitted in an Armv8 implementation. 0b0000 Performance Monitors Extension not implemented. 0b0001 Performance Monitors Extension, PMUv1 implemented. 0b0010 Performance Monitors Extension, PMUv2 implemented. 0b0011 Performance Monitors Extension, PMUv3 implemented. 0b0100 PMUv3 for Armv8.1. As 0b0011, and adds support for: Extended 16-bit PMEVTYPER<n>.evtCount field. If EL2 is implemented, the HDCR.HPMD control. 0b0101 PMUv3 for Armv8.4. As 0b0100, and adds support for the PMMIR register. 0b0110 PMUv3 for Armv8.5. As 0b0101, and adds support for: 64-bit event counters. If EL2 is implemented, the HDCR.HCCD control. If EL3 is implemented, the SDCR.SCCD control. 0b0111 PMUv3 for Armv8.7. As 0b0110, and adds support for: The PMCR.FZO and, if EL2 is implemented, HDCR.HPMFZO controls. If EL3 is implemented and using AArch64, the MDCR_EL3.{MPMX,MCCD} controls. 0b1000 PMUv3 for Armv8.8. As 0b0111, and: Extends the Common event number space to include 0x0040 to 0x00BF and 0x4040 to 0x40BF. Removes the CONSTRAINED UNPREDICTABLE behaviors if a reserved or unimplemented PMU event number is selected. 0b1001 PMUv3 for Armv8.9. As 0b1000, and: Updates the definitions of existing PMU events. Adds support for the EDECR.PME control. 0b1111 IMPLEMENTATION DEFINED form of performance monitors supported, PMUv3 not supported. Arm does not recommend this value for new implementations. RO MProfDbg 23 20 23:20 M-profile Debug. Support for memory-mapped debug model for M-profile processors. All other values are reserved. In Armv8, the only permitted value is 0b0000. 0b0000 Not supported. 0b0001 Support for M-profile Debug architecture, with memory-mapped access. RO MMapTrc 19 16 19:16 Memory-mapped Trace. Support for memory-mapped trace model. All other values are reserved. In Armv8, the permitted values are 0b0000 and 0b0001. For more information, see the Arm® Embedded Trace Macrocell Architecture Specification, ETMv4 (ARM IHI 0064). 0b0000 Not supported. 0b0001 Support for Arm trace architecture, with memory-mapped access. RO CopTrc 15 12 15:12 Support for System registers-based trace model, using registers in the coproc == 0b1110 encoding space. All other values are reserved. In Armv8, the permitted values are 0b0000 and 0b0001. For more information, see the Arm® Embedded Trace Macrocell Architecture Specification, ETMv4 (ARM IHI 0064). 0b0000 Not supported. 0b0001 Support for Arm trace architecture, with System registers access. RO MMapDbg 11 8 11:8 Memory-mapped Debug. Support for Armv7 memory-mapped debug model for A and R-profile processors. All other values are reserved. In Armv8, the only permitted value is 0b0000. The optional memory map defined by Armv8 is not compatible with Armv7. 0b0000 Not supported. 0b0100 Support for Armv7, v7 Debug architecture, with memory-mapped access. 0b0101 Support for Armv7, v7.1 Debug architecture, with memory-mapped access. RO CopSDbg 7 4 7:4 Support for a System registers-based Secure debug model, using registers in the coproc = 0b1110 encoding space, for an A-profile processor that includes EL3. If EL3 is not implemented and the implemented Security state is Non-secure state, this field is RES0. Otherwise, this field reads the same as bits [3:0]. This field has an IMPLEMENTATION DEFINED value. RO CopDbg 3 0 3:0 Debug architecture version. Indicates presence of Armv8 debug architecture. All other values are reserved. The values 0b0000, 0b0010, 0b0011, 0b0100, and 0b0101 are not permitted in Armv8. FEAT_Debugv8p1 implements the functionality identified by the value 0b0111. FEAT_Debugv8p2 implements the functionality identified by the value 0b1000. FEAT_Debugv8p4 implements the functionality identified by the value 0b1001. FEAT_Debugv8p8 implements the functionality identified by the value 0b1010. FEAT_Debugv8p9 implements the functionality identified by the value 0b1011. From Armv8.1, when FEAT_Debugv8p1 is implemented the value 0b0110 is not permitted. From Armv8.2, the values 0b0110 and 0b0111 are not permitted. From Armv8.4, the value 0b1000 is not permitted. From Armv8.8, the value 0b1001 is not permitted. From Armv8.9, the value 0b1010 is not permitted. 0b0000 Not supported. 0b0010 Armv6, v6 Debug architecture, with System registers access. 0b0011 Armv6, v6.1 Debug architecture, with System registers access. 0b0100 Armv7, v7 Debug architecture, with System registers access. 0b0101 Armv7, v7.1 Debug architecture, with System registers access. 0b0110 Armv8 debug architecture. 0b0111 Armv8.1 debug architecture, FEAT_Debugv8p1. 0b1000 Armv8.2 debug architecture, FEAT_Debugv8p2. 0b1001 Armv8.4 debug architecture, FEAT_Debugv8p4. 0b1010 Armv8.8 debug architecture, FEAT_Debugv8p8. 0b1011 Armv8.9 debug architecture, FEAT_Debugv8p9. RO MRC{<c>}{<q>} <coproc>, {#}<opc1>, <Rt>, <CRn>, <CRm>{, {#}<opc2>} if !IsFeatureImplemented(FEAT_AA32EL1) then Undefined(); elsif PSTATE.EL == EL0 then Undefined(); elsif PSTATE.EL == EL1 then if EL2Enabled() && IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2) && HSTR_EL2().T0 == '1' then AArch64_AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && IsFeatureImplemented(FEAT_AA32EL2) && ELUsingAArch32(EL2) && HSTR().T0 == '1' then AArch32_TakeHypTrapException(0x03); elsif EL2Enabled() && IsFeatureImplemented(FEAT_AA64EL2) && !ELUsingAArch32(EL2) && HCR_EL2().TID3 == '1' then AArch64_AArch32SystemAccessTrap(EL2, 0x03); elsif EL2Enabled() && IsFeatureImplemented(FEAT_AA32EL2) && ELUsingAArch32(EL2) && HCR().TID3 == '1' then AArch32_TakeHypTrapException(0x03); else R(t) = ID_DFR0(); end; elsif PSTATE.EL == EL2 then R(t) = ID_DFR0(); elsif PSTATE.EL == EL3 then R(t) = ID_DFR0(); end; 2026-03-26 20:27:25 2026-03_rel