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System control processor (CP15) registers
52
NS9750 Hardware Reference
Accessing CP15 registers
Use only MRC and MCR instructions, only in privileged mode, to access CP15 registers.
Figure 11 shows the MRC and MCR instruction bit pattern.
Figure 11: 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
If you try to read from a write-only register or write to a read-only register, you will
have
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 operations you want. 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 behavior you want. Using other values
results in unpredictable behavior.
Terms and abbreviations
Table 17 lists the terms and abbreviations used in the CP15 registers and
explanations.
Cond
1110 1111 1L
Opcode
_1
Opcode
_2
CRn CRmRd
31 28 27 26 25 24 23 21 20 19 16 15 12 11 10 9 8 7 5 4 3 0
Term Abbreviation Description
UNPREDICTABLE UNP For reads:
The data returned when reading from this location is
unpredictable, and can have any value.
For writes:
Writing to this location causes unpredictable
behavior, or an unpredictable change in device
configuration.
Table 17: CP15 terms and abbreviations