AT91SAM9261 datasheet(53/688 Pages) ATMEL

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6062F–ATARM–05-Dec-06

AT91SAM9261 Preliminary

11.4.1

CP15 Registers Access

CP15 registers can only be accessed in privileged mode by:

• MCR (Move to Coprocessor from ARM Register) instruction is used to write an ARM

• MRC (Move to ARM Register from Coprocessor) instruction is used to read the value of

CP15 to an ARM register.

Other instructions like CDP, LDC, STC can cause an undefined instruction exception.

The assembler code for these instructions is:

MCR/MRC{cond} p15, opcode_1, Rd, CRn, CRm, opcode_2.

The MCR, MRC instructions bit pattern is shown below:

• CRm[3:0]: Specified Coprocessor Action

Determines specific coprocessor action. Its value is dependent on the CP15 register used. For details, refer to CP15 spe-

cific register behavior.

• opcode_2[7:5]

Determines specific coprocessor operation code. By default, set to 0.

• Rd[15:12]: ARM Register

Defines the ARM register whose value is transferred to the coprocessor. If R15 is chosen, the result is unpredictable.

• CRn[19:16]: Coprocessor Register

Determines the destination coprocessor register.

• L: Instruction Bit

0 = MCR instruction

1 = MRC instruction

• opcode_1[23:20]: Coprocessor Code

Defines the coprocessor specific code. Value is c15 for CP15.

• cond [31:28]: Condition

For more details, see Chapter 2 in ARM926EJ-S TRM, ref. DDI0198B.

cond

1110

opcode_1

CRn

1111

543210

opcode_2

CRm

AT91SAM9261 Datasheet(PDF) 53 Page - ATMEL Corporation