ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Debug Register Interfaces
C6.1 About the debug register interfaces
The Debug architecture defines a set of debug registers. The debug register interfaces provide access to these
registers. This chapter describes the different ways of implementing the debug register interfaces.
The debug register interfaces provide access to the debug registers from:
software running on the processor, see Processor interface to the debug registers
an external debugger, see External interface to the debug registers.
The debug register interfaces always include the Debug Communications Channel, see The Debug
Communications Channel (DCC) on page C6-3.
C6.1.1 Processor interface to the debug registers
Table C6-4 on page C6-32 lists the set of CP14 debug instructions for accessing the debug registers that
must be implemented.
The possible interfaces between the software running on the processor and the debug registers are:
The Baseline CP14 interface. This provides access to a small set of the debug registers through a set
of coprocessor instructions. It must be implemented by all processors.
The Extended CP14 interface. This provides access to the remaining debug registers through a
coprocessor interface. It is required in v6 Debug and v6.1 Debug, and is optional in v7 Debug.
The memory-mapped interface. This provides memory-mapped access to the debug registers. It is
introduced in v7 Debug, and is an optional interface. When it is implemented:
— some of the registers that are accessed through the Baseline CP14 interface are not available
through the memory-mapped interface
— it is IMPLEMENTATION DEFINED whether the memory-mapped interface is visible only to the
processor in which the debug registers are implemented, or is also visible to other processors
in the system.
An ARMv7 implementation must include the Baseline CP14 interface and at least one of:
the Extended CP14 interface
the memory-mapped interface.
C6.1.2 External interface to the debug registers
Every ARMv6 and ARMv7 implementation must include an external debug interface. This interface
provides access to the debug registers from an external debugger through a Debug Access Port (DAP). This
interface is IMPLEMENTATION DEFINED. For details of the interface recommended by ARM:
for an ARMv7 implementation, see the ARM Debug Interface v5 Architecture Specification
for an ARMv6 implementation, contact ARM.
C6-2 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B