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The PowerPC Core
6-20
MPC801 USER’S MANUAL
MOTOROLA
6
6.3.1.2 BIT ASSIGNMENT OF THE CONTROL REGISTERS
6.3.1.2.1 Machine State Register.
The 32-bit machine state register (MSR) defines the
state of the processor. It can be read by the
mfmsr
instruction.
Bits 0–12—Reserved
These bits are reserved and should be set to 0. Bits 0, 5, and 9 are loaded from the
corresponding bit in the MSR when an interrupt is taken. The appropriate bit in the MSR is
loaded from this bit when an
rfi
is executed. Reserved bits in the MSR are set from the
source value on write and return the value last set for it on read.
POW—Power Management Enable
Power management may not exist on all implementations. If it is not implemented, this bit is
reserved.
0 = Power management is disabled (normal operation mode).
1 = Power management is enabled (reduced power mode).
Bit 14—Reserved
This bit is reserved and should be set to 0.
ILE—Interrupt Little-Endian Mode
When an interrupt occurs, this bit is copied to MSR
LE
to select the endian mode for the
context established by the interrupt.
EE—External Interrupt Enable
0 = The processor is disabled against external and decrementer interrupts.
1 = The processor is enabled to take an external or decrementer interrupt.
PR—Problem State
0 = The processor is privileged to execute any instruction.
1 = The processor can only execute the nonprevileged instructions.
FP—Floating-Point Available
0 = The processor cannot execute any floating-point instructions, including
floating-point loads, stores, or moves.
1 = The processor can execute floating-point instructions.
MSR
BIT
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
FIELD
RESERVED
POW
RES
ILE
BIT
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
FIELD
EE
PR
FP
ME
FE0
SE
BE
FE1
RES
IP
IR
DR
RESERVED
RI
LE