Atomic Variables
[User API: Pico Layer]


Functions

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

POSEXTERN INT_t 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 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 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 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

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