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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
702 of 808
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 User Guide
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 ignored. Fault handlers can examine EPSR value in the stacked PSR to
indicate the operation that is at fault. See
Interruptible-continuable instructions:
When an interrupt occurs during the execution
of an
LDM
or
STM
instruction, the processor:
After servicing the interrupt, the processor:
•
stops the load multiple or store multiple instruction operation temporarily.
•
stores the next register operand in the multiple operation to EPSR bits[15:12].
•
returns to the register pointed to by bits[15:12].
•
resumes execution of the multiple load or store instruction.
When the EPSR holds ICI execution state, bits[26:25,11:10] are zero.
If-Then block:
The If-Then block contains up to four instructions following a 16-bit
IT
instruction. Each instruction in the block is conditional. The conditions for the instructions
are either all the same, or some can be the inverse of others. See
for more information.
3.1.3.6
Exception mask registers
The exception mask registers disable the handling of exceptions by the processor.
Disable exceptions where they might impact on timing critical tasks.
To access the exception mask registers use the
MSR
and
MRS
instructions, or the
CPS
instruction to change the value of PRIMASK or FAULTMASK. See
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 shown in
Fault Mask Register:
The FAULTMASK register prevents activation of all exceptions
except for
Non-Maskable Interrupt
(NMI). See the register summary in
its attributes. The bit assignments are shown in
The processor clears the FAULTMASK bit to 0 on exit from any exception handler except
the NMI handler.
Table 603.
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.
Table 604.
FAULTMASK register bit assignments
Bits
Name
Function
[31:1]
-
Reserved
[0]
FAULTMASK
0 = no effect
1 = prevents the activation of all exceptions except for NMI.