System Control Coprocessor
ARM DDI 0301H Copyright © 2004-2009 ARM Limited. All rights reserved. 3-128
ID012310 Non-Confidential, Unrestricted Access
3.2.47 c13, Context ID Register
The purpose of the Context ID Register is to provide information on the current ASID and
process ID, for example for the ETM and debug logic.
Table 3-129 lists the purposes of the individual bits of the Context ID Register.
Debug logic uses the ASID information to enable process-dependent breakpoints and
watchpoints.
The Context ID Register is:
• in CP15 c13
• a 32-bit read/write register banked for Secure and Non-secure worlds
• accessible in privileged modes only.
Writing to this register globally flushes the BTAC.
Figure 3-70 shows the arrangement of bits in the Context ID Register.
Figure 3-70 Context ID Register format
Table 3-129 lists how the bit values correspond with the Context ID Register functions.
Table 3-130 lists the results of attempted access for each mode.
The current ASID value in the ID Context Register is exported to the MMU.
To use the Context ID Register read or write CP15 with:
• Opcode_1 set to 0
• CRn set to c13
• CRm set to c0
• Opcode_2 set to 1.
For example:
MRC p15, 0, <Rd>, c13, c0, 1 ;Read Context ID Register
PROCID
31 8 7 0
ASID
Table 3-129 Context ID Register bit functions
Bits Field name Function
[31:8] PROCID Extends the ASID to form the process ID and identify the current process.
The value is the Process ID. The reset value is 0.
[8:0] ASID Holds the ASID of the current process to identify the current ASID.
The value is the ASID. The reset value is 0.
Table 3-130 Results of access to the Context ID Register
Secure Privileged Non-secure Privileged
User
Read Write Read Write
Secure data Secure data Non-secure data Non-secure data Undefined exception
To Next Page
Loading...
Need help?
General
