DBGWCR<n>_EL1, Debug Watchpoint Control Registers, n = 0 - 15

The DBGWCR<n>_EL1 characteristics are:

Purpose

Holds control information for a watchpoint. Forms watchpoint n together with value register DBGWVR<n>_EL1.

Configuration

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

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

DBGWCR<n>_EL1 is in the Core power domain.

If watchpoint n is not implemented then accesses to this register are:

• When IsCorePowered() && !DoubleLockStatus() && !OSLockStatus() && AllowExternalDebugAccess(), RES0.
• Otherwise, a CONSTRAINED UNPREDICTABLE choice of RES0 or ERROR.

Attributes

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

Field descriptions

The DBGWCR<n>_EL1 bit assignments are:

Bits [31:29]

Reserved, RES0.

MASK, bits [28:24]

Address mask. Only objects up to 2GB can be watched using a single mask.

If programmed with a reserved value, a watchpoint must behave as if either:

• MASK has been programmed with a defined value, which might be 0 (no mask), other than for a direct read of DBGWCRn_EL1.
• The watchpoint is disabled.

Software must not rely on this property because the behavior of reserved values might change in a future revision of the architecture.

Other values mask the corresponding number of address bits, from 0b00011 masking 3 address bits (0x00000007 mask for address) to 0b11111 masking 31 address bits (0x7FFFFFFF mask for address).

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

Bits [23:21]

Reserved, RES0.

WT, bit [20]

Watchpoint type. Possible values are:

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

LBN, bits [19:16]

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

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 Watchpoint debug event for watchpoint n is generated. This field must be interpreted along with the HMC and PAC fields.

For more information on the operation of the SSC, HMC, and PAC fields, see 'Execution conditions for which a watchpoint generates Watchpoint exceptions'.

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 Watchpoint debug event for watchpoint n is generated. This field must be interpreted along with the SSC and PAC fields.

For more information on the operation of the SSC, HMC, and PAC fields, see 'Execution conditions for which a watchpoint generates Watchpoint exceptions'.

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

BAS, bits [12:5]

Byte address select. Each bit of this field selects whether a byte from within the word or double-word addressed by DBGWVR<n>_EL1 is being watched.

In cases where DBGWVR<n>_EL1 addresses a double-word:

If DBGWVR<n>_EL1[2] == 1, only BAS[3:0] is used. Arm deprecates setting DBGWVR<n>_EL1[2] == 1.

The valid values for BAS are non-zero binary number all of whose set bits are contiguous. All other values are reserved and must not be used by software. See 'Reserved DBGWCR<n>.BAS values'.

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

LSC, bits [4:3]

Load/store control. This field enables watchpoint matching on the type of access being made. Possible values of this field are:

All other values are reserved, but must behave as if the watchpoint is disabled. Software must not rely on this property as the behavior of reserved values might change in a future revision of the architecture.

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

PAC, bits [2:1]

Privilege of access control. Determines the Exception level or levels at which a Watchpoint debug event for watchpoint n is generated. This field must be interpreted along with the SSC and HMC fields.

For more information on the operation of the SSC, HMC, and PAC fields, see 'Execution conditions for which a watchpoint generates Watchpoint exceptions'.

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

E, bit [0]

Enable watchpoint n. Possible values are:

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

Accessing the DBGWCR<n>_EL1

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

This interface is accessible as follows:

• When IsCorePowered(), !DoubleLockStatus(), !OSLockStatus(), AllowExternalDebugAccess() and SoftwareLockStatus() accesses to this register are RO.
• When IsCorePowered(), !DoubleLockStatus(), !OSLockStatus(), AllowExternalDebugAccess() and !SoftwareLockStatus() accesses to this register are RW.
• Otherwise accesses to this register generate an error response.