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User manual Rev. 3 — 20 December 2013  677 of 841
NXP Semiconductors
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Chapter 34: Appendix: Cortex-M3 user guide
34.2.4.9 CLREX
Clear Exclusive. 
34.2.4.9.1 Syntax
CLREX{cond}
where:
cond is an optional condition code, see Section 34.2.3.7 “
Conditional execution”.
34.2.4.9.2 Operation
Use 
CLREX
 to make the next 
STREX
, 
STREXB
, or 
STREXH
 instruction write 1 to its destination 
register and fail to perform the store. It is useful in exception handler code to force the 
failure of the store exclusive if the exception occurs between a load exclusive instruction 
and the matching store exclusive instruction in a synchronization operation.
See Section 34.3.2.7 “
Synchronization primitives” for more information.
34.2.4.9.3 Condition flags
These instructions do not change the flags.
34.2.4.9.4 Examples
CLREX