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March 2002 Release
Virtex-II Pro™ Platform FPGA Documentation
1-800-255-7778
Privileged Registers
R
Special-Purpose Registers
All privileged PPC405 registers except for the machine-state register are
special-purpose
registers
, or SPRs. See
for a complete list
of all SPRs (user and privileged) supported by the PPC405.
SPRs are read and written using the
move from special-purpose register
(
mfspr
) and
move to
special-purpose register
(
mtspr
) instructions. See
Special-Purpose Register Instructions
, for more information on these instructions. Simplified instruction mnemonics
are available for the
mtspr
and
mfspr
instructions when accessing certain SPRs. See
, for more information.
Machine-State Register
The machine-state register (MSR) is a 32-bit register that defines the processor state.
shows the format of the MSR. The bits in the MSR are defined as shown in
. All system software can read and write the MSR using the
move from machine-
state register
(
mfmsr
) and
move to machine-state register
(
mtmsr
) instructions. The external-
interrupt enable (MSR[EE]) bit can also be updated using the
write external enable
instructions (
wrtee
and
wrteei
Machine-State Register Instructions
, for
more information on these instructions.
The MSR is also modified during execution of the
system-call
instruction (
sc
),
return-from-
interrupt
instructions (
rfi
and
rfci
), and by the exception mechanism during a control
transfer to an interrupt handler.
0
6
12
13
14
16
17
18
19
20
21
22
23
26
27
31
AP
APE
WE
CE
EE
PR
FP
ME
FE0 DWE
DE
FE1
IR
DR
Figure 4-2:
Machine-State Register (MSR)
Table 4-1:
Machine-State Register (MSR) Bit Definitions
Bit
Name
Function
Description
0:5
Reserved
6
AP
Auxiliary Processor Available
(Unsupported)
This bit is unsupported and ignored by the PPC405D5. Software
should clear this bit to 0.
7:11
Reserved
12
APE
APU Exception Enable
(Unsupported)
This bit is unsupported and ignored by the PPC405D5. Software
should clear this bit to 0.
13
WE
Wait State Enable
0—Disabled.
1—Enabled.
When in the wait state, the processor stops fetching and executing
instructions, and no longer performs memory accesses. The
processor remains in the wait state until an interrupt or a reset
occurs, or an external debug tool clears WE. See
, for more information.
14
CE
Critical Interrupt Enable
0—Disabled.
1—Enabled.
Controls the critical-input interrupt and the watchdog-timer
interrupt. See
, for more information
on these interrupts.
15
Reserved
16
EE
External Interrupt Enable
0—Disabled.
1—Enabled.
Controls the external interrupts, the programmable-interval timer
interrupt, and the fixed-interval timer interrupt. See
, for more information on each interrupt.
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