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DBGBCR<n>, Debug Breakpoint Control Registers, n = 0 - 15

The DBGBCR<n> characteristics are:

Purpose

Holds control information for a breakpoint. Forms breakpoint n together with value register DBGBVR<n>. If EL2 is implemented and this breakpoint supports Context matching, DBGBVR<n> can be associated with a Breakpoint Extended Value Register DBGBXVR<n> for VMID matching.

Configuration

AArch32 System register DBGBCR<n> bits [31:0] are architecturally mapped to AArch64 System register DBGBCR<n>_EL1[31:0] .

AArch32 System register DBGBCR<n> bits [31:0] are architecturally mapped to External register DBGBCR<n>_EL1[31:0] .

If breakpoint n is not implemented then accesses to this register are UNDEFINED.

This register is in the Cold reset domain. On a Cold reset RW fields in this register reset to architecturally UNKNOWN values. The register is not affected by a Warm reset.

Attributes

DBGBCR<n> is a 32-bit register.

Field descriptions

The DBGBCR<n> bit assignments are:

313029282726252423222120191817161514131211109876543210
RES0BTLBNSSCHMCRES0BASRES0PMCE

When the E field is zero, all the other fields in the register are ignored.

Bits [31:24]

Reserved, RES0.

BT, bits [23:20]

Breakpoint Type. Possible values are:

BTMeaning
0b0000

Unlinked instruction address match. DBGBVR<n> is the address of an instruction.

0b0001

As 0b0000 with linking enabled.

0b0010

Unlinked Context ID match. When ARMv8.1-VHE is implemented, EL2 is using AArch64, and the Effective value of HCR_EL2.E2H is 1, if either the PE is executing at EL0 with HCR_EL2.TGE set to 0 or the PE is executing at EL2, then DBGBVR<n>.ContextID must match the CONTEXTIDR_EL2 value. Otherwise DBGBVR<n>.ContextID must match the CONTEXTIDR value.

0b0011

As 0b0010 with linking enabled.

0b0100

Unlinked instruction address mismatch. DBGBVR<n> is the address of an instruction to be stepped.

0b0101

As 0b0100 with linking enabled.

0b0110

Unlinked CONTEXTIDR_EL1 match. DBGBVR<n>.ContextID is a Context ID compared against CONTEXTIDR.

0b0111

As 0b0110 with linking enabled.

0b1000

Unlinked VMID match. DBGBXVR<n>.VMID is a VMID compared against VTTBR.VMID.

0b1001

As 0b1000 with linking enabled.

0b1010

Unlinked VMID and Context ID match. DBGBVR<n>.ContextID is a Context ID compared against CONTEXTIDR, and DBGBXVR<n>.VMID is a VMID compared against VTTBR.VMID.

0b1011

As 0b1010 with linking enabled.

0b1100

Unlinked CONTEXTIDR_EL2 match. DBGBXVR<n>.ContextID2 is a Context ID compared against CONTEXTIDR_EL2.

0b1101

As 0b1100 with linking enabled.

0b1110

Unlinked Full Context ID match. DBGBVR<n>.ContextID is compared against CONTEXTIDR, and DBGBXVR<n>.ContextID2 is compared against CONTEXTIDR_EL2.

0b1111

As 0b1110 with linking enabled.

For more information on Breakpoints and their constraints, see 'Breakpoint exceptions' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G2.9 and 'Reserved DBGBCR<n>.BT values' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G2 (AArch32 Self-hosted Debug).

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

LBN, bits [19:16]

Linked breakpoint number. For Linked address matching breakpoints, this specifies the index of the Context-matching breakpoint linked to.

For all other breakpoint types this field is ignored and reads of the register return an UNKNOWN value.

This field is ignored when the value of DBGBCR<n>.E is 0.

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

SSC, bits [15:14]

Security state control. Determines the Security states under which a Breakpoint debug event for breakpoint n is generated. This field must be interpreted along with the HMC and PMC fields, and there are constraints on the permitted values of the {HMC, SSC, PMC} fields.

For more information, see 'Execution conditions for which a breakpoint generates Breakpoint exceptions' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, and 'Reserved DBGBCR<n>.{SSC, HMC, PMC} values' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile.

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

HMC, bit [13]

Higher mode control. Determines the debug perspective for deciding when a Breakpoint debug event for breakpoint n is generated. This field must be interpreted along with the SSC and PMC fields, and there are constraints on the permitted values of the {HMC, SSC, PMC} fields. For more information see the SSC, bits [15:14] description.

For more information on the operation of the SSC, HMC, and PMC fields, see 'Execution conditions for which a breakpoint generates Breakpoint exceptions' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G2 (AArch32 Self-hosted Debug).

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

Bits [12:9]

Reserved, RES0.

BAS, bits [8:5]

Byte address select. Defines which half-words an address-matching breakpoint matches, regardless of the instruction set and Execution state.

The permitted values depend on the breakpoint type.

For Address match breakpoints, the permitted values are:

BASMatch instruction atConstraint for debuggers
0b0011DBGBVR<n>Use for T32 instructions
0b1100DBGBVR<n>+2Use for T32 instructions
0b1111DBGBVR<n>Use for A32 instructions

All other values are reserved. For more information, see 'Reserved DBGBCR<n>.BAS values' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G2 (AArch32 Self-hosted Debug).

For more information on using the BAS field in Address Match breakpoints, see 'Using the BAS field in Address Match breakpoints' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G2 (AArch32 Self-hosted Debug).

For Address mismatch breakpoints in an AArch32 stage 1 translation regime, the permitted values are:

BASStep instruction atConstraint for debuggers
0b0000-Use for a match anywhere breakpoint
0b0011DBGBVR<n>Use for T32 instructions
0b1100DBGBVR<n>+2Use for T32 instructions
0b1111DBGBVR<n>Use for A32 instructions

All other values are reserved. For more information, see 'Reserved DBGBCR<n>.BAS values' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G2 (AArch32 Self-hosted Debug).

For more information on using the BAS field in address mismatch breakpoints, see 'Using the BAS field in Address Match breakpoints' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G2 (AArch32 Self-hosted Debug).

For Context matching breakpoints, this field is RES1 and ignored.

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

Bits [4:3]

Reserved, RES0.

PMC, bits [2:1]

Privilege mode control. Determines the Exception level or levels at which a Breakpoint debug event for breakpoint n is generated. This field must be interpreted along with the SSC and HMC fields, and there are constraints on the permitted values of the {HMC, SSC, PMC} fields. For more information see the DBGBCR<n>.SSC description.

For more information on the operation of the SSC, HMC, and PMC fields, see 'Execution conditions for which a breakpoint generates Breakpoint exceptions' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section G2 (AArch32 Self-hosted Debug).

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

E, bit [0]

Enable breakpoint DBGBVR<n>. Possible values are:

EMeaning
0b0

Breakpoint disabled.

0b1

Breakpoint enabled.

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

Accessing the DBGBCR<n>

Accesses to this register use the following encodings:

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

coprocopc1CRnCRmopc2
0b11100b0000b0000n[3:0]0b101
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);
    elsif ELUsingAArch32(EL1) && DBGOSLSR.OSLK == '0' && HaltingAllowed() && EDSCR.TDA == '1' then
        Halt(DebugHalt_SoftwareAccess);
    else
        return DBGBCR[UInt(CRm<3:0>)];
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && !ELUsingAArch32(EL3) && MDCR_EL3.TDA == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x05);
    elsif ELUsingAArch32(EL1) && DBGOSLSR.OSLK == '0' && HaltingAllowed() && EDSCR.TDA == '1' then
        Halt(DebugHalt_SoftwareAccess);
    else
        return DBGBCR[UInt(CRm<3:0>)];
elsif PSTATE.EL == EL3 then
    if ELUsingAArch32(EL1) && DBGOSLSR.OSLK == '0' && HaltingAllowed() && EDSCR.TDA == '1' then
        Halt(DebugHalt_SoftwareAccess);
    else
        return DBGBCR[UInt(CRm<3:0>)];
              

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

coprocopc1CRnCRmopc2
0b11100b0000b0000n[3:0]0b101
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);
    elsif ELUsingAArch32(EL1) && DBGOSLSR.OSLK == '0' && HaltingAllowed() && EDSCR.TDA == '1' then
        Halt(DebugHalt_SoftwareAccess);
    else
        DBGBCR[UInt(CRm<3:0>)] = R[t];
elsif PSTATE.EL == EL2 then
    if HaveEL(EL3) && !ELUsingAArch32(EL3) && MDCR_EL3.TDA == '1' then
        AArch64.AArch32SystemAccessTrap(EL3, 0x05);
    elsif ELUsingAArch32(EL1) && DBGOSLSR.OSLK == '0' && HaltingAllowed() && EDSCR.TDA == '1' then
        Halt(DebugHalt_SoftwareAccess);
    else
        DBGBCR[UInt(CRm<3:0>)] = R[t];
elsif PSTATE.EL == EL3 then
    if ELUsingAArch32(EL1) && DBGOSLSR.OSLK == '0' && HaltingAllowed() && EDSCR.TDA == '1' then
        Halt(DebugHalt_SoftwareAccess);
    else
        DBGBCR[UInt(CRm<3:0>)] = R[t];
              


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