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

The DBGWCR<n> characteristics are:

Purpose

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

This register is part of the Debug registers functional group.

Configuration

There is one instance of this register that is used in both Secure and Non-secure states.

AArch32 System register DBGWCR<n> is architecturally mapped to AArch64 System register DBGWCR<n>_EL1.

AArch32 System register DBGWCR<n> is architecturally mapped to External register DBGWCR<n>_EL1.

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

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

DBGWCR<n> is a 32-bit register.

Field descriptions

The DBGWCR<n> bit assignments are:

313029282726252423222120191817161514131211109876543210
000MASK000WTLBNSSCHMCBASLSCPACE

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

Bits [31:29]

Reserved, RES0.

MASK, bits [28:24]

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

MASKMeaning
00000

No mask.

00001

Reserved.

00010

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).

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

Bits [23:21]

Reserved, RES0.

WT, bit [20]

Watchpoint type. Possible values are:

WTMeaning
0

Unlinked data address match.

1

Linked data address match.

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

LBN, bits [19:16]

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

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

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' in the ARMv8 ARM, section G2 (AArch32 Self-hosted Debug).

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

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' in the ARMv8 ARM, section G2 (AArch32 Self-hosted Debug).

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

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> is being watched.

BAS Description
xxxxxxx1 Match byte at DBGWVR<n>
xxxxxx1x Match byte at DBGWVR<n>+1
xxxxx1xx Match byte at DBGWVR<n>+2
xxxx1xxx Match byte at DBGWVR<n>+3

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

BAS Description, if DBGWVR<n>[2] == 0
xxx1xxxx Match byte at DBGWVR<n>+4
xx1xxxxx Match byte at DBGWVR<n>+5
x1xxxxxx Match byte at DBGWVR<n>+6
1xxxxxxx Match byte at DBGWVR<n>+7

If DBGWVR<n>[2] == 1, only BAS[3:0] are used and BAS[7:4] are ignored. ARM deprecates setting DBGWVR<n>[2] == 1.

The valid values for BAS are non-zero binary numbers 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' in the ARMv8 ARM, section G2 (AArch32 Self-hosted Debug)

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

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
01

Match instructions that load from a watchpointed address.

10

Match instructions that store to a watchpointed address.

11

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.

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

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' in the ARMv8 ARM, section G2 (AArch32 Self-hosted Debug).

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

E, bit [0]

Enable watchpoint n. Possible values are:

EMeaning
0

Watchpoint disabled.

1

Watchpoint enabled.

When this register has an architecturally-defined reset value, this field resets to a value that is architecturally UNKNOWN.

Accessing the DBGWCR<n>

This register can be read using MRC with the following syntax:

MRC <syntax>

This register can be written using MCR with the following syntax:

MCR <syntax>

This syntax uses the following encoding in the System instruction encoding space:

<syntax> opc1opc2CRncoprocCRm
p14, 0, <Rt>, c0, <CRm>, 700011100001110n<3:0>

Accessibility

The register is accessible as follows:

Control Accessibility
E2HTGENSEL0EL1EL2EL3
xx0 - RW n/a RW
x01 - RWRWRW
x11 - n/a RWRW

This table applies to all instructions that can access this register.

Traps and enables

For a description of the prioritization of any generated exceptions, see section G1.11.2 (Exception priority order) in the ARM® Architecture Reference Manual, ARMv8, for ARMv8-A architecture profile for exceptions taken to AArch32 state, and section D1.13.2 (Synchronous exception prioritization) for exceptions taken to AArch64 state. Subject to the prioritization rules, the following traps and enables are applicable when accessing this register.

In both Security states, and not dependent on other configuration bits:

When EL2 is implemented and is using AArch64 and SCR_EL3.NS==1 :

When EL2 is implemented and is using AArch32 and SCR_EL3.NS==1 :

When EL3 is implemented and is using AArch64 :




18/04/2017 17:00

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