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

Protected Memory System Architecture (PMSA)
B4.6.34 c13, Context ID Register (CONTEXTIDR)
The Context ID Register, CONTEXTIDR, identifies the current context by means of a Context Identifier
(Context ID).
Note
Previously, on PMSA implementations, this Context ID has been described as a Process Identifier
(PROCID), and this CP15 c13 register has been called the Process ID Register. The new naming makes the
register naming consistent for PMSA and VMSA implementations.
The whole of this register is used by:
the debug logic, for Linked and Unlinked Context ID matching, see Breakpoint debug events on
page C3-5 and Watchpoint debug events on page C3-15.
the trace logic, to identify the current process.
The CONTEXTIDR is:
a 32-bit read/write register
accessible only in privileged modes.
The format of the CONTEXTIDR is:
31 0
ContextID
ContextID, bits [31:0]
Context Identifier. This field must be programmed with a unique context identifier value that
identifies the current process. It is used by the trace logic and the debug logic to identify the
process that is running currently.
Accessing the CONTEXTIDR
To access the CONTEXTIDR you read or write the CP15 registers with set to 0, set to c13,
set to c0, and set to 1. For example:
MRC p15,0,,c13,c0,1 ; Read CP15 Context ID Register
MCR p15,0,,c13,c0,1 ; Write CP15 Context ID Register
B4-76 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B