UM10462
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User manual
Rev. 5.5 — 21 December 2016
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NXP Semiconductors
UM10462
Chapter 24: LPC11U3x/2x/1x Appendix ARM Cortex-M0
Attempts by application software to read the EPSR directly using the
MRS
instruction
always return zero. Attempts to write the EPSR using the
MSR
instruction are ignored.
Fault handlers can examine the EPSR value in the stacked PSR to determine the cause
of the fault. See
. The following can clear the T bit to 0:
•
instructions
BLX
,
BX
and
POP{PC}
•
restoration from the stacked xPSR value on an exception return
•
bit[0] of the vector value on an exception entry.
Attempting to execute instructions when the T bit is 0 results in a HardFault or lockup. See
for more information.
Interruptible-restartable instructions:
The interruptible-restartable instructions are
LDM
and
STM
. When an interrupt occurs during the execution of one of these instructions, the
processor abandons execution of the instruction.
After servicing the interrupt, the processor restarts execution of the instruction from the
beginning.
24.3.1.3.6
Exception mask register
The exception mask register disables the handling of exceptions by the processor.
Disable exceptions where they might impact on timing critical tasks or code sequences
requiring atomicity.
To disable or re-enable exceptions, use the
MSR
and
MRS
instructions, or the
CPS
instruction, to change the value of PRIMASK. See
,
, and
for more information.
Priority Mask Register:
The PRIMASK register prevents activation of all exceptions with
configurable priority. See the register summary in
for its attributes. The bit
assignments are:
24.3.1.3.7
CONTROL register
The CONTROL register controls the stack used when the processor is in Thread mode.
See the register summary in
for its attributes. The bit assignments are:
Table 417. EPSR bit assignments
Bits
Name
Function
[31:25]
-
Reserved
[24]
T
Thumb state bit
[23:0]
-
Reserved
Table 418. PRIMASK register bit assignments
Bits
Name
Function
[31:1]
-
Reserved
[0]
PRIMASK
0 = no effect
1 = prevents the activation of all exceptions with
configurable priority.