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)

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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.

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Function Documentation

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

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

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

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