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Instruction Cache
MCF5253 Reference Manual, Rev. 1
5-8
Freescale Semiconductor
5.5.2.2
Access Control Registers
The access control registers ACR0 and ACR1, provide a definition of memory reference attributes for two
memory regions (one per ACR). This set of effective attributes is defined for every memory reference
using the ACRs or the set of default attributes contained in the CACR. The ACRs are examined for every
memory reference that is NOT mapped to the SRAM module.
The ACRs are 32-bit write-only supervisor control registers. They are accessed in the CPU address space
using the MOVEC instruction with an Rc encoding of $004 and $005. The ACRs can be read when in
background debug mode (BDM). At system reset, the registers are cleared.
Address MOVEC with $004
MOVEC with $005
Access: User read/write
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
R
BA31 BA30 BA29 BA28 BA27 BA26 BA25 BA24 BAM31 BAM30 BAM29 BAM28 BAM27 BAM26 BAM25 BAM24
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
R
EN
SM1 SM0
CM
BWE
WP
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Figure 5-3. Access Control Registers (ACR0, ACR1)
Table 5-6. Access Control Registers Field Descriptions
Bit Name
Description
31–24
BA
The Base Address. An 8-bit field compared to the 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.
23–16
BAM
The Base 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.
15
EN
The Enable bit defines the ACR enable. Hardware reset clears this bit, disabling the ACR.
0 ACR disabled
1 ACR enabled
14–13
SM1, SM0
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
12–7
Reserved, should be cleared.
6
CM
The Cache Mode bit defines the cache mode: 0 is cacheable, 1 is noncacheable.
0 Caching enabled
1 Caching disabled
Содержание MCF5253
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Страница 26: ...MCF5253 Reference Manual Rev 1 xxvi Freescale Semiconductor...
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