
Instruction Cache Programming Model
MOTOROLA
Instruction Cache
5-9
Table 5-8 Access Control Bit Descriptions
BIT NAME
DESCRIPTION
AB[31:24]
The Address Base [31:24] 8-bit field is compared to address bits [31:24] from the
processor's local bus under control of the ACR address mask. If the address
matches, the attributes for the memory reference are sourced from the given ACR.
AM[31:24]
The Address Mask [31:24] 8-bit field can mask any bit of the AB field comparison. If
a bit in the AM field is set, then the corresponding bit of the address field
comparison is ignored.
EN
The Enable bit defines the ACR enable. Hardware reset clears this bit, disabling the
ACR.
0 = ACR disabled
1 = ACR enabled
SM[1:0]
The Supervisor mode two-bit field allows the given ACR to be applied to references
based on operating privilege mode of the ColdFire processor. The field uses the
ACR for user references only, supervisor references only, or all accesses.
00 = Match if user mode
01 = Match if supervisor mode
1x = Match always - ignore user/supervisor mode
CM
The Cache Mode bit defines the cache mode: 0 is cacheable, 1 is noncacheable.
0 = Caching enabled
1 = Caching disabled
BWE
The Buffered Write Enable bit defines the value for enabling buffered writes. If BWE
= 0, the termination of an operand write cycle on the processor's local bus is
delayed until the external bus cycle is completed. If BWE = 1, the write cycle on the
local bus is terminated immediately and the operation is then buffered in the bus
controller. In this mode, operand write cycles are effectively decoupled between the
processor's local bus and the external bus.
Generally, the enabling of buffered writes provides higher system performance but
recovery from access errors may be more difficult. For the ColdFire CPU, the
reporting of access errors on operand writes is always imprecise, and enabling
buffered writes simply decouples the write instruction from the signaling of the fault
even more.
0 = Don’t buffer writes
1 = Buffer writes
WP
The Write Protect bit defines the write-protection attribute. If the effective memory
attributes for a given access select the WP bit, an access error terminates any
attempted write with this bit set.
0 = Read and write accesses permitted
1 = Only read accesses permitted
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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