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DBGDSCRext, Debug Status and Control Register, External View

The DBGDSCRext characteristics are:

Purpose

Main control register for the debug implementation.

Configuration

AArch32 System register DBGDSCRext bits [31:0] are architecturally mapped to AArch64 System register MDSCR_EL1[31:0] .

AArch32 System register DBGDSCRext bits [15:2] are architecturally mapped to AArch32 System register DBGDSCRint[15:2] .

This register is required in all implementations.

This register is in the Warm reset domain. Some or all RW fields of this register have defined reset values. On a Warm or Cold reset these apply only if the PE resets into an Exception level that is using AArch32. Otherwise, on a Warm or Cold reset RW fields in this register reset to architecturally UNKNOWN values.

Attributes

DBGDSCRext is a 32-bit register.

Field descriptions

The DBGDSCRext bit assignments are:

TFO, bit [31]

When ARMv8.4-Trace is implemented:

Trace Filter override. Used for save/restore of EDSCR.TFO.

When the OS Lock is unlocked, OSLSR_EL1.OSLK == 0, this bit ignores writes and software must treat it as UNK/SBZP.

When the OS Lock is locked, OSLSR_EL1.OSLK == 1, this bit is RW and holds the value of EDSCR.TFO.

Reads and writes of this bit are indirect accesses to EDSCR.TFO.


Otherwise:

Reserved, RES0.

RXfull, bit [30]

DTRRX full. Used for save/restore of EDSCR.RXfull.

When OSLSR_EL1.OSLK == 0, this bit is RO, and software must treat it as UNK/SBZP.

When OSLSR_EL1.OSLK == 1, this bit is RW and holds the value of EDSCR.RXfull.

Arm deprecates use of this bit other than for save/restore. Use DBGDSCRint to access the DTRRX full status.

Reads and writes of this bit are indirect accesses to EDSCR.RXfull.

The architected behavior of this field determines the value it returns after a reset.

TXfull, bit [29]

DTRTX full. Used for save/restore of EDSCR.TXfull.

When OSLSR_EL1.OSLK == 0, this bit is RO, and software must treat it as UNK/SBZP.

When DBGOSLSR.OSLK == 1, this bit is RW and holds the value of EDSCR.TXfull.

Arm deprecates use of this bit other than for save/restore. Use DBGDSCRint to access the DTRTX full status.

Reads and writes of this bit are indirect accesses to EDSCR.TXfull.

The architected behavior of this field determines the value it returns after a reset.

Bit [28]

Reserved, RES0.

RXO, bit [27]

Used for save/restore of EDSCR.RXO.

When OSLSR_EL1.OSLK == 0, this bit is RO, and software must treat it as UNK/SBZP.

When DBGOSLSR.OSLK == 1, this bit is RW and holds the value of EDSCR.RXO.

Reads and writes of this bit are indirect accesses to EDSCR.RXO.

The architected behavior of this field determines the value it returns after a reset.

TXU, bit [26]

Used for save/restore of EDSCR.TXU.

When OSLSR_EL1.OSLK == 0, this bit is RO, and software must treat it as UNK/SBZP.

When DBGOSLSR.OSLK == 1, this bit is RW and holds the value of EDSCR.TXU.

Reads and writes of this bit are indirect accesses to EDSCR.TXU.

The architected behavior of this field determines the value it returns after a reset.

Bits [25:24]

Reserved, RES0.

INTdis, bits [23:22]

Used for save/restore of EDSCR.INTdis.

When OSLSR_EL1.OSLK == 0, this field is RO, and software must treat it as UNK/SBZP.

When DBGOSLSR.OSLK == 1, this field is RW and holds the value of EDSCR.INTdis.

Reads and writes of this field are indirect accesses to EDSCR.INTdis.

The architected behavior of this field determines the value it returns after a reset.

TDA, bit [21]

Used for save/restore of EDSCR.TDA.

When OSLSR_EL1.OSLK == 0, this bit is RO, and software must treat it as UNK/SBZP.

When DBGOSLSR.OSLK == 1, this bit is RW and holds the value of EDSCR.TDA.

Reads and writes of this bit are indirect accesses to EDSCR.TDA.

The architected behavior of this field determines the value it returns after a reset.

Bit [20]

Reserved, RES0.

SC2, bit [19]

When ARMv8.0-PCSample is implemented, ARMv8.1-VHE is implemented and ARMv8.2-PCSample is not implemented:

Used for save/restore of EDSCR.SC2.

When DBGOSLSR.OSLK == 0, this bit is RO, and software must treat it as UNK/SBZP.

When DBGOSLSR.OSLK == 1, this bit is RW and holds the value of EDSCR.SC2.

Reads and writes of this bit are indirect accesses to EDSCR.SC2.


Otherwise:

Reserved, RES0.

NS, bit [18]

Non-secure status. Returns the inverse of IsSecure(). This bit is RO.

Arm deprecates use of this field.

SPNIDdis, bit [17]

Secure privileged profiling disabled status bit. This bit is RO. Permitted values are:

SPNIDdisMeaning
0b0

If EL3 is implemented, profiling allowed in Secure privileged modes.

0b1

If EL3 is implemented, profiling prohibited in Secure privileged modes.

This field is RES0 if EL3 is not implemented.

  • Otherwise, the field reads as zero if any of the following applies, and reads as one otherwise:
    • ARMv8.2-Debug is not implemented and ExternalSecureNoninvasiveDebugEnabled() returns TRUE.
    • EL3 is using AArch32 and the value of SDCR.SPME is 1.
    • EL3 is using AArch64 and the value of MDCR_EL3.SPME is 1.

Arm deprecates use of this field.

SPIDdis, bit [16]

Secure privileged AArch32 invasive self-hosted debug disabled status bit. This bit is RO and depends on the value of SDCR.SPD and the pseudocode function AArch32.SelfHostedSecurePrivilegedInvasiveDebugEnabled(). Permitted values are:

SPIDdisMeaning
0b0

Self-hosted debug enabled in Secure privileged AArch32 modes.

0b1

Self-hosted debug disabled in Secure privileged AArch32 modes.

This bit reads as 1 if any of the following is true and reads as 0 otherwise:

  • SDCR.SPD has the value 0b10.
  • SDCR.SPD has the value 0b00 and SelfHostedSecurePrivilegedInvasiveDebugEnabled() returns FALSE.

Arm deprecates use of this field.

MDBGen, bit [15]

Monitor debug events enable. Enable Breakpoint, Watchpoint, and Vector Catch exceptions.

MDBGenMeaning
0b0

Breakpoint, Watchpoint, and Vector Catch exceptions disabled.

0b1

Breakpoint, Watchpoint, and Vector Catch exceptions enabled.

On a Warm reset, this field resets to 0.

HDE, bit [14]

Used for save/restore of EDSCR.HDE.

When OSLSR_EL1.OSLK == 0, this bit is RO, and software must treat it as UNK/SBZP.

When DBGOSLSR.OSLK == 1, this bit is RW and holds the value of EDSCR.HDE.

Reads and writes of this bit are indirect accesses to EDSCR.HDE.

The architected behavior of this field determines the value it returns after a reset.

Bit [13]

Reserved, RES0.

UDCCdis, bit [12]

Traps EL0 accesses to the DCC registers to Undefined mode.

UDCCdisMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL0 accesses to the DBGDSCRint, DBGDTRRXint, DBGDTRTXint, DBGDIDR, DBGDSAR, and DBGDRAR are trapped to Undefined mode.

Note

All accesses to these registers are trapped, including LDC and STC accesses to DBGDTRTXint and DBGDTRRXint, and MRRC accesses to DBGDSAR and DBGDRAR.

Traps of EL0 accesses to the DBGDTRRXint and DBGDTRTXint are ignored in Debug state.

On a Warm reset, this field resets to 0.

Bits [11:7]

Reserved, RES0.

ERR, bit [6]

Used for save/restore of EDSCR.ERR.

When OSLSR_EL1.OSLK == 0, this bit is RO, and software must treat it as UNK/SBZP.

When DBGOSLSR.OSLK == 1, this bit is RW and holds the value of EDSCR.ERR.

Reads and writes of this bit are indirect accesses to EDSCR.ERR.

The architected behavior of this field determines the value it returns after a reset.

MOE, bits [5:2]

Method of Entry for debug exception. When a debug exception is taken to an Exception level using AArch32, this field is set to indicate the event that caused the exception:

MOEMeaning
0b0001

Breakpoint.

0b0011

Software breakpoint (BKPT) instruction.

0b0101

Vector catch.

0b1010

Watchpoint.

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

Bits [1:0]

Reserved, RES0.

Accessing the DBGDSCRext

Individual fields within this register might have restricted accessibility when the OS lock is unlocked, DBGOSLSR.OSLK == 0. See the field descriptions for more detail.

Accesses to this register use the following encodings:

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

coprocopc1CRnCRmopc2
0b11100b0000b00000b00100b010
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && MDCR_EL2.<TDE,TDA> != '00' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x05);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HDCR.<TDE,TDA> != '00' then
        AArch32.TakeHypTrapException(0x05);
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && MDCR_EL3.TDA == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x05);
    else
        return DBGDSCRext;
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && !ELUsingAArch32(EL3) && MDCR_EL3.TDA == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x05);
    else
        return DBGDSCRext;
elsif PSTATE.EL == EL3 then
    return DBGDSCRext;
              

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

coprocopc1CRnCRmopc2
0b11100b0000b00000b00100b010
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && MDCR_EL2.<TDE,TDA> != '00' then
        AArch64.AArch32SystemAccessTrap(EL2, 0x05);
    elsif EL2Enabled() && ELUsingAArch32(EL2) && HDCR.<TDE,TDA> != '00' then
        AArch32.TakeHypTrapException(0x05);
    elsif HaveEL(EL3) && !ELUsingAArch32(EL3) && MDCR_EL3.TDA == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x05);
    else
        DBGDSCRext = R[t];
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && !ELUsingAArch32(EL3) && MDCR_EL3.TDA == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x05);
    else
        DBGDSCRext = R[t];
elsif PSTATE.EL == EL3 then
    DBGDSCRext = R[t];
              


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