Instruction Cache Programming Model
MOTOROLA
Instruction Cache
5-5
5.4
INSTRUCTION CACHE PROGRAMMING MODEL
Three supervisor registers define the operation of the instruction cache and local bus controller: the Cache
Control Register (CACR) and two Access Control Registers (ACR0, ACR1).
5.4.1
INSTRUCTION CACHE REGISTERS MEMORY MAP
Table 5-3 shows the memory map of the Instruction cache and access control registers.
The following list describes several key issues regarding the programming model table:
The Cache Control Register and Access Control Registers can only be accessed in supervisor mode
using the MOVEC instruction with an Rc value of $002, $004 and $005, respectively.
Addresses not assigned to the registers and undefined register bits are reserved for future
expansion. Write accesses to these reserved address spaces and reserved register bits have no
effect; read accesses will return zeros.
The reset value column indicates the initial value of the register at reset. Certain registers may be
uninitialized upon reset, i.e., they may contain random values after reset.
The access column indicates if the corresponding register allows both read/write functionality (R/W),
read-only functionality (R), or write-only functionality (W). If a read access to a write-only register is
attempted, zeros will be returned. If a write access to a read-only register is attempted the access will be
ignored and no write will occur.
Table 5-2 Instruction Cache Operation as Defined by CACR[31,10]
CACR[31]
CACR[10]
TYPE OF
INSTR. FETCH
DESCRIPTION
0
N/A
Instruction cache is completely disabled; all fetches are
word, longword in size.
0
1
N/A
All fetches are word, longword in size
1
X
Cacheable
Fetch size is defined by Table 4-1 and contents of the
line-fill buffer can be written into the memory array
1
0
Noncacheable
All fetches are longword in size, and not loaded into the
line-fill buffer
1
Noncacheable
Fetch size is defined by Table 4-1 and loaded into the
line-fill buffer, but are never written into the memory
array.
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