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EDDEVARCH, External Debug Device Architecture register

The EDDEVARCH characteristics are:


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


It is IMPLEMENTATION DEFINED whether EDDEVARCH is implemented in the Core power domain or in the Debug power domain.

Implementation of this register is OPTIONAL.

If ARMv8.3-DoPD is implemented, this register is in the Core power domain. If ARMv8.3-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.

ARMv8.4-Debug adds the functionality indicated by the value 0b1001. ARMv8.2-Debug adds the functionality indicated by the value 0b1000. If ARMv8.1-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 ARMv8.3-DoPD is not implemented or IsCorePowered() accesses to this register are RO.
  • Otherwise accesses to this register generate an error response.