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MDCR_EL3, Monitor Debug Configuration Register (EL3)

The MDCR_EL3 characteristics are:

Purpose

Provides EL3 configuration options for self-hosted debug and the Performance Monitors Extension.

Configuration

AArch64 System register MDCR_EL3 bits [31:0] can be mapped to AArch32 System register SDCR[31:0] , but this is not architecturally mandated.

This register is present only when HaveEL(EL3). Otherwise, direct accesses to MDCR_EL3 are UNDEFINED.

Some or all RW fields of this register have defined reset values. These apply only if the PE resets into an Exception level that is using AArch64. Otherwise, RW fields in this register reset to architecturally UNKNOWN values.

Attributes

MDCR_EL3 is a 64-bit register.

Field descriptions

The MDCR_EL3 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0
RES0MTPMETDCCRES0NSTBSCCDETADEPMADEDADTTRFSTESPMESDDSPD32NSPBRES0TDOSATDARES0TPMRES0
313029282726252423222120191817161514131211109876543210

Bits [63:29]

Reserved, RES0.

MTPME, bit [28]

When ARMv8.6-MTPMU is implemented:

Multi-threaded PMU Enable. Enables use of the PMEVTYPER<n>_EL0.MT bits.

MTPMEMeaning
0b0

ARMv8.6-MTPMU is disabled. The Effective value of PMEVTYPER<n>_EL0.MT is zero.

0b1

PMEVTYPER<n>_EL0.MT bits not affected by this bit.

If ARMv8.6-MTPMU is disabled for any other PE in the system that has the same level 1 Affinity as the PE, it is IMPLEMENTATION DEFINED whether the PE behaves as if this bit is 0.

On a Cold reset, this field resets to 1.


Otherwise:

Reserved, RES0.

TDCC, bit [27]

When ARMv8.6-FGT is implemented:

Trap DCC. Traps use of the Debug Comms Channel at EL2, EL1, and EL0 to EL3.

TDCCMeaning
0b0

This control does not cause any register accesses to be trapped.

0b1

Accesses to the DCC registers at EL2, EL1, and EL0 generate a Trap exception to EL3, unless the access also generates a higher priority exception.

Traps on the DCC data transfer registers are ignored when the PE is in Debug state.

The DCC registers trapped by this control are:

AArch64: OSDTRRX_EL1, OSDTRTX_EL1, MDCCSR_EL0, MDCCINT_EL1, and, when the PE is in Non-debug state, DBGDTR_EL0, DBGDTRRX_EL0, and DBGDTRTX_EL0.

AArch32: DBGDTRRXext, DBGDTRTXext, DBGDSCRint, DBGDCCINT, and, when the PE is in Non-debug state, DBGDTRRXint and DBGDTRTXint.

The traps are reported with EC syndrome value:

  • 0x05 for trapped AArch32 MRC and MCR accesses with coproc == 0b1110.

  • 0x06 for trapped AArch32 LDC to DBGDTRTXint and STC from DBGDTRRXint.

  • 0x18 for trapped AArch64 MRS and MSR accesses.

When the PE is in Debug state, MDCR_EL3.TDCC does not trap any accesses to:

AArch64: DBGDTR_EL0, DBGDTRRX_EL0, and DBGDTRTX_EL0.

AArch32: DBGDTRRXint and DBGDTRTXint.

On a Warm reset, this field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

Bit [26]

Reserved, RES0.

NSTB, bits [25:24]

When TRBE is implemented:

Non-secure Trace Buffer. Controls the owning translation regime and accesses to Trace Buffer control registers from EL2 and EL1.

NSTBMeaning
0b00

Trace Buffer owning security state is Secure state. If TraceBufferEnabled() == TRUE, tracing is prohibited in Non-secure state. Accesses to Trace Buffer control registers at EL2 and EL1 generate Trap exceptions to EL3.

0b01

Trace Buffer owning security state is Secure state. If TraceBufferEnabled() == TRUE, tracing is prohibited in Non-secure state. Accesses to Trace Buffer control registers at EL2 and EL1 in Non-secure state generate Trap exceptions to EL3.

0b10

Trace Buffer owning security state is Non-secure state. If TraceBufferEnabled() == TRUE, tracing is prohibited in Secure state. Accesses to Trace Buffer control registers at EL2 and EL1 generate Trap exceptions to EL3.

0b11

Trace Buffer owning security state is Non-secure state. If TraceBufferEnabled() == TRUE, tracing is prohibited in Secure state. Accesses to Trace Buffer control registers at EL2 and EL1 in Secure state generate Trap exceptions to EL3.

The Trace Buffer control registers trapped by this control are: TRBBASER_EL1, TRBLIMITR_EL1, TRBMAR_EL1, TRBPTR_EL1, TRBSR_EL1, and TRBTRG_EL1.

If EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b1, the PE behaves as if this field is 0b11. If EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, the PE behaves as if this field is 0b01.

On a Warm reset, this field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

SCCD, bit [23]

When ARMv8.5-PMU is implemented:

Secure Cycle Counter Disable. Prohibits PMCCNTR_EL0 from counting in Secure state.

SCCDMeaning
0b0

Cycle counting by PMCCNTR_EL0 is not affected by this bit.

0b1

Cycle counting by PMCCNTR_EL0 is prohibited in Secure state.

This bit does not affect the CPU_CYCLES event or any other event that counts cycles.

On a Warm reset, this field resets to 0.


Otherwise:

Reserved, RES0.

ETAD, bit [22]

When TRBE is implemented:

External Trace Non-secure Access Disable. Controls Non-secure access to PE Trace Unit registers by an external debugger.

ETADMeaning
0b0

Non-secure accesses from an external debugger to PE Trace Unit are allowed.

0b1

Non-secure accesses from an external debugger to PE Trace Unit are prohibited.

If the Trace Extension does not support external debug interface accesses this bit is RES0.

Otherwise, if EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this field is 0b1.

On a Warm reset, this field resets to 0.


Otherwise:

Reserved, RES0.

EPMAD, bit [21]

When ARMv8.4-Debug is implemented and PMUv3 is implemented:

External Performance Monitors Non-secure Access Disable. Controls Non-secure access to Performance Monitor registers by an external debugger.

EPMADMeaning
0b0

Non-secure access to Performance Monitor registers from external debugger is permitted.

0b1

Non-secure access to Performance Monitor registers from external debugger is not permitted.

If the Performance Monitors Extension does not support external debug interface accesses this bit is RES0.

Otherwise, if EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this bit is 0b1.

On a Warm reset, this field resets to 0.


When PMUv3 is implemented:

External Performance Monitors Access Disable. Controls access to Performance Monitor registers by an external debugger.

EPMADMeaning
0b0

Access to Performance Monitor registers from external debugger is permitted.

0b1

Access to Performance Monitor registers from external debugger is not permitted, unless overridden by the IMPLEMENTATION DEFINED authentication interface.

If the Performance Monitors Extension does not support external debug interface accesses this bit is RES0.

Otherwise, if EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this bit is 0b1.

On a Warm reset, this field resets to 0.


Otherwise:

Reserved, RES0.

EDAD, bit [20]

When ARMv8.4-Debug is implemented:

External Debug Non-secure Access Disable. Controls Non-secure access to breakpoint, watchpoint, and OSLAR_EL1 registers by an external debugger.

EDADMeaning
0b0

Non-secure access to debug registers from external debugger is permitted.

0b1

Non-secure access to breakpoint and watchpoint registers, and OSLAR_EL1 from external debugger is not permitted.

If EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this field is 0b1.

On a Warm reset, this field resets to 0.


When ARMv8.2-Debug is implemented:

External Debug Access Disable. Controls access to breakpoint, watchpoint, and OSLAR_EL1 registers by an external debugger.

EDADMeaning
0b0

Access to debug registers, and to OSLAR_EL1 from external debugger is permitted.

0b1

Access to breakpoint and watchpoint registers, and to OSLAR_EL1 from external debugger is not permitted, unless overridden by the IMPLEMENTATION DEFINED authentication interface.

If EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this field is 0b1.

On a Warm reset, this field resets to 0.


Otherwise:

External Debug Access disable. Controls access to breakpoint, watchpoint, and optionally OSLAR_EL1 registers by an external debugger.

EDADMeaning
0b0

Access to debug registers from external debugger is permitted.

0b1

Access to breakpoint and watchpoint registers from an external debugger is not permitted, unless overridden by the IMPLEMENTATION DEFINED authentication interface.

It is IMPLEMENTATION DEFINED whether access to the OSLAR_EL1 register from an external debugger is permitted or not permitted.

If EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this field is 0b1.

On a Warm reset, this field resets to 0.

TTRF, bit [19]

When ARMv8.4-Trace is implemented:

Trap Trace Filter controls. Traps use of the Trace Filter control registers at EL2 and EL1 to EL3.

The Trace Filter registers trapped by this control are:

TTRFMeaning
0b0

Accesses to Trace Filter registers at EL2 and EL1 are not affected by this bit.

0b1

Accesses to Trace Filter registers at EL2 and EL1 generate a Trap exception to EL3, unless the access generates a higher priority exception.


Otherwise:

Reserved, RES0.

STE, bit [18]

When ARMv8.4-Trace is implemented:

Secure Trace enable. Enables tracing in Secure state.

STEMeaning
0b0

Trace prohibited in Secure state unless overridden by the IMPLEMENTATION DEFINED authentication interface.

0b1

Trace in Secure state is not affected by this bit.

This bit also controls the level of authentication required by an external debugger to enable external tracing. See 'Register controls to enable self-hosted trace' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile.

If EL3 is not implemented the Effective value of SCR_EL3.NS is 0b0, the Effective value of this bit is 0b1.

On a Warm reset, this field resets to 0.


Otherwise:

Reserved, RES0.

SPME, bit [17]

When ARMv8.2-Debug is implemented and PMUv3 is implemented:

Secure Performance Monitors enable. This allows event counting in Secure state.

SPMEMeaning
0b0

Event counting prohibited in Secure state.

0b1

Event counting in Secure state not affected by this bit.

If EL3 is not implemented the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this bit is 0b1.

On a Warm reset, this field resets to 0.


When PMUv3 is implemented:

Secure Performance Monitors enable. This allows event counting in Secure state.

SPMEMeaning
0b0

Event counting prohibited in Secure state, unless ExternalSecureNoninvasiveDebugEnabled() is TRUE.

0b1

Event counting in Secure state not affected by this bit.

If EL3 is not implemented the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this bit is 0b1.

On a Warm reset, this field resets to 0.


Otherwise:

Reserved, RES0.

SDD, bit [16]

AArch64 Secure Self-hosted invasive debug disable. Disables Software debug exceptions in Secure state, other than Breakpoint Instruction exceptions.

SDDMeaning
0b0

Debug exceptions in Secure state are not affected by this bit.

0b1

Debug exceptions, other than Breakpoint Instruction exceptions, are disabled from all Exception levels in Secure state.

The SDD bit is ignored unless both of the following are true:

  • The PE is in Secure state.
  • The Effective value of SCR_EL3.RW is 0b1.

On a Warm reset, this field resets to an architecturally UNKNOWN value.

SPD32, bits [15:14]

AArch32 Secure self-hosted privileged debug. Enables or disables debug exceptions from Secure EL1 using AArch32, other than Breakpoint Instruction exceptions.

SPD32Meaning
0b00

Legacy mode. Debug exceptions from Secure EL1 are enabled by the IMPLEMENTATION DEFINED authentication interface.

0b10

Secure privileged debug disabled. Debug exceptions from Secure EL1 are disabled.

0b11

Secure privileged debug enabled. Debug exceptions from Secure EL1 are enabled.

Other values are reserved, and have the CONSTRAINED UNPREDICTABLE behavior that they must have the same behavior as 0b00. Software must not rely on this property as the behavior of reserved values might change in a future revision of the architecture.

This field has no effect on Breakpoint Instruction exceptions. These are always enabled.

This field is:

  • Ignored if the PE is either:
    • In Non-secure state.
    • In Secure state and Secure EL1 is using AArch64.
  • RES0 if the implementation does not support EL1 using AArch32.

If Secure EL1 is using AArch32 then:

  • If debug exceptions from Secure EL1 are enabled, then debug exceptions from Secure EL0 are also enabled.
  • Otherwise, debug exceptions from Secure EL0 are enabled only if the value of SDER32_EL3.SUIDEN is 0b1.

If EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, then the Effective value of this field is 0b11.

On a Warm reset, this field resets to an architecturally UNKNOWN value.

NSPB, bits [13:12]

When SPE is implemented:

Non-secure Profiling Buffer. This field controls the owning translation regime and accesses to Statistical Profiling and Profiling Buffer control registers.

NSPBMeaning
0b00

Profiling Buffer uses Secure Virtual Addresses. Statistical Profiling enabled in Secure state and disabled in Non-secure state. Accesses to Statistical Profiling and Profiling Buffer control registers at EL2 and EL1 in both security states generate Trap exceptions to EL3.

0b01

Profiling Buffer uses Secure Virtual Addresses. Statistical Profiling enabled in Secure state and disabled in Non-secure state. Accesses to Statistical Profiling and Profiling Buffer control registers at EL2 and EL1 in Non-secure state generate Trap exceptions to EL3.

0b10

Profiling Buffer uses Non-secure Virtual Addresses. Statistical Profiling enabled in Non-secure state and disabled in Secure state. Accesses to Statistical Profiling and Profiling Buffer control registers at EL2 and EL1 in both security states generate Trap exceptions to EL3.

0b11

Profiling Buffer uses Non-secure Virtual Addresses. Statistical Profiling enabled in Non-secure state and disabled in Secure state. Accesses to Statistical Profiling and Profiling Buffer control registers at EL2 and EL1 in Secure state generate Trap exceptions to EL3.

The Statistical Profiling and Profiling Buffer control registers trapped by this control are: PMBLIMITR_EL1, PMBPTR_EL1, PMBSR_EL1, PMSCR_EL1, PMSCR_EL2, PMSEVFR_EL1, PMSFCR_EL1, PMSICR_EL1, PMSIDR_EL1, PMSIRR_EL1, and PMSLATFR_EL1.

If EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b1, the Effective value of this field is 0b11. If EL3 is not implemented and the Effective value of SCR_EL3.NS is 0b0, the Effective value of this field is 0b01.

On a Warm reset, this field resets to an UNKNOWN value.


Otherwise:

Reserved, RES0.

Bit [11]

Reserved, RES0.

TDOSA, bit [10]

When ARMv8.0-DoubleLock is implemented:

Trap debug OS-related register access. Traps EL2 and EL1 System register accesses to the powerdown debug registers to EL3.

Accesses to the registers are trapped as follows:

  • Accesses from AArch64 state, OSLAR_EL1, OSLSR_EL1, OSDLR_EL1, DBGPRCR_EL1 and any IMPLEMENTATION DEFINED register with similar functionality that the implementation specifies as trapped by this bit, are trapped to EL3 and reported using EC syndrome value 0x18.
  • Accesses using MCR or MRC to DBGOSLAR, DBGOSLSR, DBGOSDLR, and DBGPRCR, are trapped to EL3 and reported using EC syndrome value 0x05.
  • Accesses to any IMPLEMENTATION DEFINED register with similar functionality that the implementation specifies as trapped by this bit.
TDOSAMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL2 and EL1 System register accesses to the powerdown debug registers are trapped to EL3, unless it is trapped by HDCR.TDOSA or MDCR_EL2.TDOSA.

Note

The powerdown debug registers are not accessible at EL0.

On a Warm reset, this field resets to an architecturally UNKNOWN value.


Otherwise:

Trap debug OS-related register access. Traps EL2 and EL1 System register accesses to the powerdown debug registers to EL3.

The following registers are affected by this trap:

TDOSAMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL2 and EL1 System register accesses to the powerdown debug registers are trapped to EL3, unless it is trapped by HDCR.TDOSA or MDCR_EL2.TDOSA.

Note

The powerdown debug registers are not accessible at EL0.

On a Warm reset, this field resets to an architecturally UNKNOWN value.

TDA, bit [9]

Trap Debug Access. Traps EL2, EL1, and EL0 System register accesses to those debug System registers that cannot be trapped using the MDCR_EL3.TDOSA field.

Accesses to the debug registers are trapped as follows:

TDAMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL0, EL1, and EL2 accesses to the debug registers, other than the registers that can be trapped by MDCR_EL3.TDOSA, are trapped to EL3, from both Security states and both Execution states, unless it is trapped by DBGDSCRext.UDCCdis, MDSCR_EL1.TDCC, HDCR.TDA or MDCR_EL2.TDA.

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Bits [8:7]

Reserved, RES0.

TPM, bit [6]

When PMUv3 is implemented:

Trap Performance Monitor register accesses. Accesses to all Performance Monitor registers from EL0, EL1 and EL2 to EL3, from both Security states and both Execution states are trapped as follows:

TPMMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL2, EL1, and EL0 System register accesses to all Performance Monitor registers are trapped to EL3, unless it is trapped by HDCR.TPM or MDCR_EL2.TPM.

On a Warm reset, this field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

Bits [5:0]

Reserved, RES0.

Accessing the MDCR_EL3

Accesses to this register use the following encodings:

MRS <Xt>, MDCR_EL3

op0op1CRnCRmop2
0b110b1100b00010b00110b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    return MDCR_EL3;
              

MSR MDCR_EL3, <Xt>

op0op1CRnCRmop2
0b110b1100b00010b00110b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    MDCR_EL3 = X[t];
              


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