Atomic Variables

Functions
POSEXTERN void POSCALL	posAtomicSet (POSATOMIC_t *var, INT_t value)
POSEXTERN INT_t POSCALL	posAtomicGet (POSATOMIC_t *var)
POSEXTERN INT_t POSCALL	posAtomicAdd (POSATOMIC_t *var, INT_t value)
POSEXTERN INT_t POSCALL	posAtomicSub (POSATOMIC_t *var, INT_t value)

Detailed Description

Atomic variables are variables that can be accessed in an atomic manner, that means a read-modify-write instruction is done in virtually one single cycle. For example, the atomic access to a variable is necessary when two tasks will do read-modify-write operations on a common variable. Under usual circumstances you can ran into trouble when a task that is just modifying the variable (that means it has read and modified the variable but has not yet written the result back) is interrupted by a second task that also modifies the variable. Thus the modification the first task has done would be lost. Atomic variables prevent this possible race condition.

pico]OS supports four functions to operate on atomic variables: posAtomicSet, posAtomicGet, posAtomicAdd and posAtomicSub.

Function Documentation

posAtomicAdd()

POSEXTERN INT_t POSCALL posAtomicAdd	(	POSATOMIC_t *	var,
		INT_t	value
	)

Atomic Variable Function. Adds a value onto the current value of the atomic variable.

Parameters

var	pointer to the atomic variable.
value	value that shall be added to the atomic variable.

Returns

the content of the atomic variable before it was incremented.

Note

POSCFG_FEATURE_ATOMICVAR must be defined to 1 to have atomic variable support compiled in.

See also

posAtomicSet, posAtomicGet, posAtomicSub

posAtomicGet()

POSEXTERN INT_t POSCALL posAtomicGet

(

POSATOMIC_t *

var

)

Atomic Variable Function. Returns the current value of an atomic variable.

Parameters

var	pointer to the atomic variable which value shall be read and returned.

Returns

the value of the atomic variable.

Note

POSCFG_FEATURE_ATOMICVAR must be defined to 1 to have atomic variable support compiled in.

See also

posAtomicSet, posAtomicAdd, posAtomicSub

posAtomicSet()

POSEXTERN void POSCALL posAtomicSet	(	POSATOMIC_t *	var,
		INT_t	value
	)

Atomic Variable Function. Sets an atomic variable to the specified value.

Parameters

var	pointer to the atomic variable that shall be set.
value	the value the atomic variable shall be set to.

Note

POSCFG_FEATURE_ATOMICVAR must be defined to 1 to have atomic variable support compiled in.

See also

posAtomicGet, posAtomicAdd, posAtomicSub

posAtomicSub()

POSEXTERN INT_t POSCALL posAtomicSub	(	POSATOMIC_t *	var,
		INT_t	value
	)

Atomic Variable Function. Substracts a value from the current value of the atomic variable.

Parameters

var	pointer to the atomic variable.
value	value that shall be substracted from the atomic variable.

Returns

the content of the atomic variable before it was decremented.

Note

POSCFG_FEATURE_ATOMICVAR must be defined to 1 to have atomic variable support compiled in.

See also

posAtomicSet, posAtomicGet, posAtomicAdd