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CHAPTER 2 V
R
4120A
156
Preliminary User’s Manual S14767EJ1V0UM00
2.5.5.8 Config register (16)
The Config register specifies various configuration options selected on V
R
4120A processors.
Some configuration options, as defined by the EC and BE fields, are set by the hardware during Cold Reset and
are included in the Config register as read-only status bits for the software to access. Other configuration options are
read/write (AD, EP, and K0 fields) and controlled by software; on Cold Reset these fields are undefined. Since only a
subset of the V
R
4000 Series options are available in the V
R
4120A, some bits are set to constants (e.g., bits 14:13)
that were variable in the V
R
4000 Series. The Config register should be initialized by software before caches are used.
Figure 2-52 shows the format of the Config register.
Figure 2-52. Config Register Format
1
1
2
2
1
23
1
1
2
19
20
21
22
17
18
15
16
14
1
3
4
28
30
24
27
31
0
EC
EP
0D
0 M16
AD
1
0
BE
13
10
1
12
CS
3
11
9
IC
3
8
6
DC
2
5
3
0
3
2
0
K0
0
IB
4
1
EC : Frequency ratio of system interface clock (VTCLK) (read only)
0 to 6
→
RFU
7
→
Pipeline clock (ACLK) frequency /1
EP : Transfer data pattern (cache write-back pattern) setting
0
→
DDDD
Others
→
RFU
AD : Accelerate data mode
0
→
V
R
4000 Series compatible mode
1
→
RFU
M16: MIPS16 ISA mode enable/disable indication (read only)
0
→
MIPS16 instruction cannot be executed
1
→
MIPS16 instruction can be executed.
BE : BigEndianMem. Endian mode of memory and a kernel.
0
→
Little endian
1
→
Big endian
CS : Cache size mode indication (fixed to 1 in the V
R
4120A)
0
→
IC = 2
1
→
IC = 2
IC : Instruction cache size indication. In the V
R
4120A, 2
4
→
16 Kbytes
Others
→
RFU
DC : Data cache size indication. In the V
R
4120A, 2
3
→
8 Kbytes
Others
→
RFU
IB : Select refill size
0
→
4 words (16 bytes)
1
→
8 words (32 bytes)
K0 : kseg0 cache coherency algorithm
010
→
Uncached
Others
→
Cached
1
: 1 is returned when read.
0
: 0 is returned when read.
(n+12)
Bytes, DC = 2
(n+12)
Bytes
(n+10)
Bytes, DC = 2
(n+10)
Bytes
(IC+10)
bytes.
(DC+10)
bytes.