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CHAPTER 2 V
R
4120A
Preliminary User’s Manual S14767EJ1V0UM00
167
2.6.3.5 Status register (12)
The Status register is a read/write register that contains the operating mode, interrupt enabling, and the diagnostic
states of the processor. Figure 2-61 shows the format of the Status register.
Figure 2-61. Status Register Format
29 28 27 26 25 24
16 15
8
7
6
5
4
3
2
1
0
31
0
CU0
0
RE
DS
IM
KX SX UX
KSU
ERL
1
2
1
3
9
EXL
IE
8
1
1
1
2
1
1
1
CU0
: Enables/disables the use of the coprocessor (1
→
Enabled, 0
→
Disabled).
CP0 can be used by the kernel at all times.
: Enables/disables reversing of the endian setting in User mode (0
→
Disabled, 1
→
Enabled).
RE
Caution
This bit must be set to 0 since the V
R
4120A CPU supports the little-endian order only.
DS
IM
: Diagnostic Status field (see Figure 2-62).
: Interrupt Mask field used to enable/disable external/internal and software interrupts (0
→
Disabled, 1
→
Enabled). This field consists of 8 bits that are used to control eight interrupts. The bits are assigned to
interrupts as follows:
IM7
: Masks a timer interrupt.
IM(6:2) :Mask ordinary interrupts (Int(4:0)
IM(1:0) : Software interrupts.
Note
). However, Int4
Note
never occur in the V
R
4120A CPU.
Note
Int(4:0) are internal signals of the CPU core. For details about connection to the on-chip
peripheral units.
KX
: Enables 64-bit addressing in Kernel mode (0
→
32-bit, 1
→
64-bit). If this bit is set, an XTLB Refill
exception occurs if a TLB miss occurs in the Kernel mode address space.
In addition, 64-bit operations are always valid in kernel mode.
: Enables 64-bit addressing and operation in Supervisor mode (0
→
32-bit, 1
→
64-bit). If this bit is set,
an XTLB Refill exception occurs if a TLB miss occurs in the Supervisor mode address space.
: Enables 64-bit addressing and operation in User mode (0
→
32-bit, 1
→
64-bit). If this bit is set, an
XTLB Refill exception occurs if a TLB miss occurs in the User mode address space.
: Sets and indicates the operating mode (10
→
User, 01
→
Supervisor, 00
→
Kernel).
: Sets and indicates the error level (0
→
Normal, 1
→
Error).
: Sets and indicates the exception level (0
→
Normal, 1
→
Exception).
: Sets and indicates interrupt enabling/disabling (0
→
Disabled, 1
→
Enabled).
: RFU. Write 0 in a write operation. When this bit is read, 0 is read.
SX
UX:
KSU
ERL
EXL
IE
0
Figure 2-62 shows the details of the Diagnostic Status (DS) field. All DS field bits other than the TS bit are writable.