Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Data Sheet

ARM DDI0198D

2-5

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

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.