User’s Manual
PPC440x5 CPU Core
Preliminary
Page 454 of 589
regsummIntro.fm.
September 12, 2002
Table 10-2 Special Purpose Registers Sorted by SPR Number on page 454, lists the Special Purpose Regis-
ters (SPRs) in order by SPR number (SPRN). The table provides mnemonics, names, SPRN, model (user or
supervisor), and access. All SPR numbers not listed are reserved, and should be neither read nor written.
Note that three registers, DBSR, MCSR, and TSR, are indicated as having the access type of read/clear.
These three registers are status registers, and as such behave differently than other SPRs when written. The
term “read/clear” does not mean that these registers are automatically cleared upon being read. Rather, the
“clear” refers to their behavior when being written. Instead of simply overwriting the SPR with the data in the
source GPR, the status SPR is updated by zeroing those bit positions corresponding to 1 values in the source
GPR, with those bit positions corresponding to 0 values in the source GPR being left unchanged. In this
fashion, it is possible for software to read one of these status SPRs, and then write to it using the same data
which was read. Any bits which were read as 1 will then be cleared, and any bits which were not yet set at the
time the SPR was read will be left unchanged. If any of these previously clear bits happen to be set between
the time the SPR is read and when it is written, then when the SPR is later read again, software will observe
any newly set bit[s]. If it were not for this behavior, then software could erroneously clear bits which it had not
yet observed as having been set, and overlook the occurrence of certain exceptions.
Table 10-2. Special Purpose Registers Sorted by SPR Number
Mnemonic
Register Name
SPRN
Model
Access
XER
Integer Exception Register
0x001
User
Read/Write
LR
Link Register
0x008
User
Read/Write
CTR
Count Register
0x009
User
Read/Write
DEC
Decrementer
0x016
Supervisor
Read/Write
SRR0
Save/Restore Register 0
0x01A
Supervisor
Read/Write
SRR1
Save/Restore Register 1
0x01B
Supervisor
Read/Write
PID
Process ID
0x030
Supervisor
Read/Write
DECAR
Decrementer Auto-Reload
0x036
Supervisor
Write-only
CSRR0
Critical Save/Restore Register 0
0x03A
Supervisor
Read/Write
CSRR1
Critical Save/Restore Register 1
0x03B
Supervisor
Read/Write
DEAR
Data Exception Address Register
0x03D
Supervisor
Read/Write
ESR
Exception Syndrome Register
0x03E
Supervisor
Read/Write
IVPR
Interrupt Vector Prefix Register
0x03F
Supervisor
Read/Write
USPRG0
User Special Purpose Register General 0
0x100
User
Read/Write
SPRG4
Special Purpose Register General 4
0x104
User
Read-only
SPRG5
Special Purpose Register General 5
0x105
User
Read-only
SPRG6
Special Purpose Register General 6
0x106
User
Read-only
SPRG7
Special Purpose Register General 7
0x107
User
Read-only
TBL
Time Base Lower
0x10C
User
Read-only
TBU
Time Base Upper
0x10D
User
Read-only
SPRG0
Special Purpose Register General 0
0x110
Supervisor
Read/Write
SPRG1
Special Purpose Register General 1
0x111
Supervisor
Read/Write
SPRG2
Special Purpose Register General 2
0x112
Supervisor
Read/Write
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