Datasheet

SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
106
MOV R1, #0x1 ; Initialize the ‘lock taken’ value try
LDREX R0, [LockAddr] ; Load the lock value
CMP R0, #0 ; Is the lock free?
ITT EQ ; IT instruction for STREXEQ and CMPEQ
STREXEQ R0, R1, [LockAddr] ; Try and claim the lock
CMPEQ R0, #0 ; Did this succeed?
BNE try ; No – try again
.... ; Yes – we have the lock
12.6.4.9 CLREX
Clear Exclusive.
Syntax
CLREX{cond}
where:
cond is an optional condition code, see “Conditional Execution” .
Operation
Use CLREX to make the next STREX, STREXB, or STREXH instruction write a 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 “Synchronization Primitives” for more information.
Condition Flags
These instructions do not change the flags.
Examples
CLREX