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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:

Attributes

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

Field descriptions

313029282726252423222120191817161514131211109876543210
LBNXRES0RES0MASKMASKRES0RES0WTWTLBNLBNSSCSSCHMCHMCBASBASLSCLSCPACPACEE

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

LBNX,Bits bits [31:3029]
When FEAT_Debugv8p9 is implemented:

Linked Breakpoint Number.

For Linked data address watchpoints, with DBGWCR<n>_EL1.LBN, specifies the index of the breakpoint linked to.

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

This field extends DBGWCR<n>_EL1.LBN to support up to 64 implemented breakpoints.

The reset behavior of this field is:


Otherwise:

Reserved, RES0.

Bit [29]

Reserved, RES0.

MASK, bits [28:24]

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

MASKMeaning
0b00000

No mask.

0b00001

Reserved.

0b00010

Reserved.

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

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).

The reset behavior of this field is:

Bits [23:21]

Reserved, RES0.

WT, bit [20]

Watchpoint type. Possible values are:

WTMeaning
0b0

Unlinked data address match.

0b1

Linked data address match.

The reset behavior of this field is:

LBN, bits [19:16]

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

For Linked data address watchpoints, with DBGWCR<n>_EL1.LBNX when implemented, specifies the index of the breakpoint linked to.

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

The reset behavior of this field is:

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'.

The reset behavior of this field is:

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'.

The reset behavior of this field is:

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.

BASDescription
xxxxxxx1Match byte at DBGWVR<n>_EL1
xxxxxx1xMatch byte at DBGWVR<n>_EL1 + 1
xxxxx1xxMatch byte at DBGWVR<n>_EL1 + 2
xxxx1xxxMatch byte at DBGWVR<n>_EL1 + 3

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

BASDescription, if DBGWVR<n>_EL1[2] == 0
xxx1xxxxMatch byte at DBGWVR<n>_EL1 + 4
xx1xxxxxMatch byte at DBGWVR<n>_EL1 + 5
x1xxxxxxMatch byte at DBGWVR<n>_EL1 + 6
1xxxxxxxMatch byte at DBGWVR<n>_EL1 + 7

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'.

The reset behavior of this field is:

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:

LSCMeaning
0b01

Match instructions that load from a watchpointed address.

0b10

Match instructions that store to a watchpointed address.

0b11

Match instructions that load from or store to a watchpointed address.

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.

The reset behavior of this field is:

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'.

The reset behavior of this field is:

E, bit [0]

Enable watchpoint n. Possible values are:

EMeaning
0b0

Watchpoint n disabled.

0b1

Watchpoint n enabled.

This bit is ignored by the PE and treated as zero when all of the following are true:

The reset behavior of this field is:

Accessing DBGWCR<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.

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

ComponentOffsetInstance
Debug0x808 + (16 * n)DBGWCR<n>_EL1

This interface is accessible as follows:


3005/0907/2022 1517:5807; 21c5a6dd0fdaf10a712e2f2d6fffbdbd66d4d96fb0421fa9a8865165f9b91af9b4a566111f866305

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