LM3S6110 Datasheet, PDF (55/610 Pages) Texas Instruments – Stellaris® LM3S6110 Microcontroller

Stellaris^® LM3S6110 Microcontroller
Register 17: Program Status Register (PSR)
Note: This register is also referred to as xPSR.
The Program Status Register (PSR) has three functions, and the register bits are assigned to the
different functions:
■ Application Program Status Register (APSR), bits 31:27,
■ Execution Program Status Register (EPSR), bits 26:24, 15:10
■ Interrupt Program Status Register (IPSR), bits 5:0
The PSR, IPSR, and EPSR registers can only be accessed in privileged mode; the APSR register
can be accessed in either privileged or unprivileged mode.
APSR contains the current state of the condition flags from previous instruction executions.
EPSR contains the Thumb state bit and the execution state bits for the If-Then (IT) instruction or
the Interruptible-Continuable Instruction (ICI) field for an interrupted load multiple or store multiple
instruction. Attempts to read the EPSR directly through application software using the MSR instruction
always return zero. Attempts to write the EPSR using the MSR instruction in application software
are always ignored. Fault handlers can examine the EPSR value in the stacked PSR to determine
the operation that faulted (see “Exception Entry and Return” on page 76).
IPSR contains the exception type number of the current Interrupt Service Routine (ISR).
These registers can be accessed individually or as a combination of any two or all three registers,
using the register name as an argument to the MSR or MRS instructions. For example, all of the
registers can be read using PSR with the MRS instruction, or APSR only can be written to using
APSR with the MSR instruction. page 55 shows the possible register combinations for the PSR. See
the MRS and MSR instruction descriptions in the Cortex™-M3/M4 Instruction Set Technical User's
Manual for more information about how to access the program status registers.
Table 2-3. PSR Register Combinations
Register
PSR
Type
R/W^{a, b}
Combination
APSR, EPSR, and IPSR
IEPSR
IAPSR
EAPSR
RO
R/W^a
R/W^b
EPSR and IPSR
APSR and IPSR
APSR and EPSR
a. The processor ignores writes to the IPSR bits.
b. Reads of the EPSR bits return zero, and the processor ignores writes to these bits.
Program Status Register (PSR)
Type R/W, reset 0x0100.0000
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
N
Z
C
V
Q
ICI / IT
THUMB
reserved
Type R/W
R/W
R/W
R/W
R/W
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
Reset
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
ICI / IT
reserved
ISRNUM
Type RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
RO
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
June 18, 2012
55
Texas Instruments-Production Data