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3: Configuration
3.2
Internal coprocessor instructions
The instruction set for the ARM720T processor enables you to implement specialized
additional instructions using coprocessors. These are separate processing units that are
coupled to the ARM720T processor, although CP15 is built into the ARM720T processor.
The CP15 register map might change in future ARM processors. You are strongly
Note:
recommended to structure software so that any code accessing CP15 is contained in
a single module, enabling it to be easily updated.
You can only access CP15 registers with MRC and MCR instructions in a privileged mode. The
instruction bit pattern of the MRC and MCR instructions is shown in Figure 3-1.
31
CDP, LDC, and STC instructions, as well as unprivileged
MRC and MCR instructions to CP15 cause the Undefined Instruction trap to be taken.
The CRn field of MRC and MCR instructions specifies the coprocessor register to access. The
CRm field and opcode_2 fields specify a particular action when addressing some registers.
In all instructions accessing CP15:
•
the opcode_1 field Should Be Zero (SBZ)
•
the opcode_2 and CRm fields Should Be Zero except when accessing registers 7, 8,
and 13 when the specified values must be used to select the desired cache, TLB, or
process identifier operations.
3-2
UNP
Figure 3-1 MRC and MCR bit pattern
EPSON
14 13 12
10 09 08 07 06 05 04 03 02 01 00
V
UNP
R S B L D P W C A M
ARM720T CORE CPU MANUAL
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