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DBGBCR<n>_EL1, Debug Breakpoint Control Registers, n = 0 - 15

The DBGBCR<n>_EL1 characteristics are:

Purpose

Holds control information for a breakpoint. Forms breakpoint n together with value register DBGBVR<n>_EL1.

Configuration

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

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

DBGBCR<n>_EL1 is in the Core power domain. RW fields in this register reset to architecturally UNKNOWN values. These apply only on a Cold reset. The register is not affected by a Warm reset and is not affected by an External debug reset.

If breakpoint n is not implemented then this register is unallocated.

Attributes

DBGBCR<n>_EL1 is a 32-bit register.

Field descriptions

The DBGBCR<n>_EL1 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>_EL1 is the address of an instruction.

0b0001

As 0b0000 but linked to a Context matching breakpoint.

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 1 or the PE is executing at EL2, then DBGBVR<n>_EL1.ContextID must match the CONTEXTIDR_EL2 value. Otherwise, DBGBVR<n>_EL1.ContextID must match the CONTEXTIDR_EL1 value.

0b0011

As 0b0010, with linking enabled.

0b0100

Unlinked instruction address mismatch. DBGBVR<n>_EL1 is the address of an instruction to be stepped.

0b0101

As 0b0100, with linking enabled.

0b0110

Unlinked CONTEXTIDR_EL1 match. DBGBVR<n>_EL1.ContextID is a Context ID compared against CONTEXTIDR_EL1.

0b0111

As 0b0110, with linking enabled.

0b1000

Unlinked VMID match. DBGBVR<n>_EL1.VMID is a VMID compared against VTTBR_EL2.VMID.

0b1001

As 0b1000, with linking enabled.

0b1010

Unlinked VMID and Context ID match. DBGBVR<n>_EL1.ContextID is a Context ID compared against CONTEXTIDR_EL1, and DBGBVR<n>_EL1.VMID is a VMID compared against VTTBR_EL2.VMID.

0b1011

As 0b1010, with linking enabled.

0b1100

Unlinked CONTEXTIDR_EL2 match. DBGBVR<n>_EL1.ContextID2 is a Context ID compared against CONTEXTIDR_EL2.

0b1101

As 0b1100, with linking enabled.

0b1110

Unlinked Full Context ID match. DBGBVR<n>_EL1.ContextID is compared against CONTEXTIDR_EL1, and DBGBVR<n>_EL1.ContextID2 is compared against CONTEXTIDR_EL2.

0b1111

As 0b1110, with linking enabled.

Constraints on breakpoint programming mean some values are reserved under certain conditions.

For more information on the operation of the SSC, HMC, and PMC fields, and on the effect of programming this field to a reserved value, see 'Execution conditions for which a breakpoint generates Breakpoint exceptions' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section D2 (AArch64 Self-hosted Debug) and 'Reserved DBGBCR<n>_EL1.BT values' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section D2 (AArch64 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>_EL1.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, including the effect of programming the fields to a reserved set of values, see 'Reserved DBGBCR<n>_EL1.{SSC, HMC, PMC} values' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section D2 (AArch64 Self-hosted Debug).

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 D2 (AArch64 Self-hosted Debug).

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 DBGBCR<n>_EL1.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 D2 (AArch64 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. In an AArch64 only implementation, this field is reserved, RES1.

The permitted values depend on the breakpoint type.

For Address match breakpoints in either AArch32 or AArch64 state, the permitted values are:

BASMatch instruction atConstraint for debuggers
0b0011DBGBVR<n>_EL1Use for T32 instructions
0b1100DBGBVR<n>_EL1 + 2Use for T32 instructions
0b1111DBGBVR<n>_EL1Use for A64 and A32 instructions

All other values are reserved.

For more information, 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:

BASMatch instruction atConstraint for debuggers
0b0000-Use for a match anywhere breakpoint
0b0011DBGBVR<n>_EL1Use for stepping T32 instructions
0b1100DBGBVR<n>_EL1 + 2Use for stepping T32 instructions
0b1111DBGBVR<n>_EL1Use for stepping A64 and A32 instructions

For more information, 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>_EL1.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 D2 (AArch64 Self-hosted Debug).

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

E, bit [0]

Enable breakpoint DBGBVR<n>_EL1. 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>_EL1

Note

SoftwareLockStatus() depends on the type of access attempted and AllowExternalDebugAccess() has a new definition from Armv8.4. Refer to the Pseudocode definitions for more information.

DBGBCR<n>_EL1 can be accessed through the external debug interface:

ComponentOffsetInstance
Debug0x408 + 16nDBGBCR<n>_EL1

This interface is accessible as follows:

  • When IsCorePowered(), !DoubleLockStatus(), !OSLockStatus(), AllowExternalDebugAccess() and SoftwareLockStatus() access to this register is RO.
  • When IsCorePowered(), !DoubleLockStatus(), !OSLockStatus(), AllowExternalDebugAccess() and !SoftwareLockStatus() access to this register is RW.
  • Otherwise access to this register returns an Error.


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