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EDDEVARCH, External Debug Device Architecture register

The EDDEVARCH characteristics are:


Identifies the programmers' model architecture of the external debug component.


Implementation of this register is OPTIONAL.

If FEAT_DoPD is implemented, this register is in the Core power domain.

If FEAT_DoPD is not implemented, this register is in the Debug power domain.


EDDEVARCH is a 32-bit register.

Field descriptions

The EDDEVARCH bit assignments are:


ARCHITECT, bits [31:21]

Defines the architecture of the component. For debug, this is Arm Limited.

Bits [31:28] are the JEP106 continuation code, 0x4.

Bits [27:21] are the JEP106 ID code, 0x3B.

PRESENT, bit [20]

When set to 1, indicates that the DEVARCH is present.

This field is 1 in Armv8.

REVISION, bits [19:16]

Defines the architecture revision. For architectures defined by Arm this is the minor revision.

For debug, the revision defined by Armv8-A is 0x0.

All other values are reserved.

ARCHVER, bits [15:12]

Defines the architecture version of the component. This is the same value as ID_AA64DFR0_EL1.DebugVer and DBGDIDR.Version. The defined values of this field are:


Armv8.0 Debug architecture.


Armv8.0 Debug architecture with Virtualization Host Extensions.


Armv8.2 Debug architecture.


Armv8.4 Debug architecture.

FEAT_Debugv8p4 adds the functionality indicated by the value 0b1001. FEAT_Debugv8p2 adds the functionality indicated by the value 0b1000. If FEAT_VHE is not implemented, the only permitted value is 0b0110.

The fields ARCHVER and ARCHPART together form the field ARCHID, so that ARCHVER is ARCHID[15:12].

ARCHPART, bits [11:0]


The part number of the Armv8-A debug component.

The fields ARCHVER and ARCHPART together form the field ARCHID, so that ARCHPART is ARCHID[11:0].

Accessing the EDDEVARCH

EDDEVARCH can be accessed through the external debug interface:


This interface is accessible as follows:

  • When FEAT_DoPD is not implemented or IsCorePowered() accesses to this register are RO.
  • Otherwise accesses to this register generate an error response.