IAR PowerPac RTOS User Guide

Counting SemaphoresIntroductionCounting semaphores are counters that are managed by IAR PowerPac RTOS. They are not as widely used as resourcesemaphores, events or mailboxes, but they can be very useful sometimes. They are used in situations where a task needsto wait for something that can be signaled one or more times. The semaphores can be accessed from any point, anytask, or any interrupt in any way.Example of using counting semaphoresOS_STACKPTR int Stack0[96], Stack1[64]; /* Task stacks */OS_TASK TCB0, TCB1; /* Data-area for tasks (task-control-blocks) */OS_CSEMA SEMALCD;void Task0(void) {Loop:Disp("Task0 will wait for task 1 to signal");OS_WaitCSema(&SEMALCD);Disp("Task1 has signaled !!");OS_Delay(100);goto Loop;}void Task1(void) {Loop:OS_Delay(5000);OS_SignalCSema(&SEMALCD);goto Loop;}void InitTask(void) {OS_CREATECSEMA(&SEMALCD); /* Create Semaphore */OS_CREATETASK(&TCB0, NULL, Task0, 100, Stack0); /* Create Task0 */OS_CREATETASK(&TCB1, NULL, Task1, 50, Stack1); /* Create Task1 */}Counting semaphores API function overviewRoutineDescriptionOS_CREATECSEMA()Macro that creates a counting semaphore with an initial count value of zero.OS_CreateCSema()Creates a counting semaphore with a specified initial count value.OS_SignalCSema()Increments the counter of a semaphore.OS_SignalCSemaMaxIncrements the counter of a semaphore up to a specified maximum value.OS_WaitCSema()Decrements the counter of a semaphore.OS_CSemaRequest()Decrements the counter of a semaphore, if available.OS_WaitCSemaTimedDecrements a semaphore counter if the semaphore is available within a specified time.OS_GetCSemaValue() Returns the counter value of a specified semaphore.OS_SetCSemaValue() Sets the counter value of a specified semaphore.OS_DeleteCSema()Returns the counter value of a specified semaphore.Table 48: Counting semaphores API overviewOS_CREATECSEMA()DescriptionMacro that creates a counting semaphore with an initial count value of zero.PPRTOS-2 55