
W O R K I N G W I T H T H E C P U
R1: Control register
88
Hardware Reference NS9215
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R 1 : C o n t r o l r e g i s t e r
Register R1 is the control register for the ARM926EJ-S processor. This register
specifies the configuration used to enable and disable the caches and MMU (memory
management unit). It is recommended that you access this register using a read-
modify-write sequence.
For both reading and writing, the
CRm
and
opcode_2
fields
SHOULD BE ZERO
. Use these
instructions to read and write this register:
MRC p15, 0, Rd, c1, c0, 0; read control register
MCR p15, Rd, c1, c0, 0; write control register
All defined control bits are set to zero on reset except the V bit and B bit.
The V bit is set to zero at reset if the
VINITHI
signal is low.
The B bit is set to zero at reset if the
BIGENDINIT
signal is low, and set to one if
the
BIGENDINIT
signal is high.
Field
Description
Size
Determines the cache size in conjunction with the M bit.
The M bit is 0 for DCache and ICache.
The size field is bits [21:18] for the DCache and bits [9:6] for the ICache.
The minimum size of each cache is 4 KB; the maximum size is 128 KB.
Cache size encoding with M=0:
Size field
Cache size
0b0011
4 KB
0b0100
8 KB
Note:
The processor always reports 4KB for DCache and 8KB for ICache.
Assoc
Determines the cache associativity in conjunction with the M bit.
The M bit is 0 for both DCache and ICache.
The assoc field is bits [17:15 for the DCache and bits [5:3] for the ICache.
Cache associativity with encoding:
Assoc field
Associativity
0b010
4-way
Other values
Reserved
M bit
Multiplier bit. Determines the cache size and cache associativity values in conjunction with
the size and assoc fields.
Note:
This field must be set to 0 for the ARM926EJ-S processor.
Len
Determines the line length of the cache.
The len field is bits [13:12] for the DCache and bits [1:0] for the ICache.
Line length encoding:
Len field
Cache line length
10
8 words (32 bytes)
Other values
Reserved
Содержание NS9215
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