Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

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SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

The processor removes its exclusive access tag if:



It executes a CLREX instruction



It executes a Store-Exclusive instruction, regardless of whether the write succeeds.



An exception occurs. This means that the processor can resolve semaphore conflicts between different threads.

In a multiprocessor implementation:



Executing a CLREX instruction removes only the local exclusive access tag for the processor



Executing a Store-Exclusive instruction, or an exception, removes the local exclusive access tags, and all global 
exclusive access tags for the processor.

 and 

.

ISO/IEC C cannot directly generate the exclusive access instructions. CMSIS provides intrinsic functions for generation
of these instructions:

The actual exclusive access instruction generated depends on the data type of the pointer passed to the intrinsic
function. For example, the following C code generates the required LDREXB operation:

__ldrex((volatile char *) 0xFF);

LDREX

uint32_t __LDREXW (uint32_t *addr)

LDREXH 

uint16_t __LDREXH (uint16_t *addr)

LDREXB

uint8_t __LDREXB (uint8_t *addr)

STREX

uint32_t __STREXW (uint32_t value, uint32_t *addr)

STREXH

uint32_t __STREXH (uint16_t value, uint16_t *addr)

STREXB

uint32_t __STREXB (uint8_t value, uint8_t *addr)

CLREX

void __CLREX (void)