Programmer’s Model
ARM DDI0198D Copyright © 2001-2003 ARM Limited. All rights reserved. 2-5
Figure 2-1 CP15 MRC and MCR bit pattern
The mnemonics for these instructions are:
MCR{cond} p15,<Opcode_1>,<Rd>,<CRn>,<CRm>,<Opcode_2>
MRC{cond} p15,<Opcode_1>,<Rd>,<CRn>,<CRm>,<Opcode_2>
Attempting to read from a write-only register, or writing to a read-only register causes
Unpredictable results. In all instructions that access CP15:
• The Opcode_1 field Should Be Zero except when the values specified are used to
select the desired operations. Using other values results in Unpredictable
behavior.
• The Opcode_2 and CRm fields Should Be Zero except when the values specified
are used to select the desired behavior. Using other values results in Unpredictable
behavior.
Table 2-3 shows the terms and abbreviations used in this chapter.
Cond
31 28 27 26 25 24 23 21 20 19 16 15 12 11 10 9 8 7 5 4 3 0
1 1 1 0
Opcode
_1
L CRn Rd 1 1 1 1
Opcode
_2
1 CRm
Table 2-3 CP15 abbreviations
Term Abbreviation Description
Unpredictable UNP For reads: The data returned when reading from
this location is unpredictable. It can have any
value.
For writes: Writing to this location causes
unpredictable behavior, or an unpredictable
change in device configuration.
Undefined UND An instruction that accesses CP15 in the manner
indicated takes the Undefined instruction
exception.
Should Be Zero SBZ When writing to this location, all bits of this field
Should Be Zero.
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