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Semaphores API Changes

Semaphores API Changes

Mar 23, 2021

The table below shows the difference in API for semaphore management.

Semaphore API

µC/OS-II (os_sem.c)

µC/OS-III (os_sem.c)

Note

INT16U OSSemAccept( OS_EVENT *pevent);

(1)

OS_EVENT * OSSemCreate( INT16U cnt);

void OSSemCreate( OS_SEM *p_sem, CPU_CHAR *p_name, OS_SEM_CTR cnt, OS_ERR *p_err);

(2)

OS_EVENT * OSSemDel( OS_EVENT *pevent, INT8U opt, INT8U *perr);

OS_OBJ_QTY, OSSemDel( OS_SEM *p_sem, OS_OPT opt, OS_ERR *p_err);

void OSSemPend( OS_EVENT *pevent, INT32U timeout, INT8U *perr);

OS_SEM_CTR OSSemPend( OS_SEM *p_sem, OS_TICK timeout, OS_OPT opt, CPU_TS *p_ts, OS_ERR *p_err);

(3)

INT8U OSSemPendAbort( OS_EVENT *pevent, INT8U opt, INT8U *perr);

OS_OBJ_QTY OSSemPendAbort( OS_SEM *p_sem, OS_OPT opt, OS_ERR *p_err);

void OSSemPost( OS_EVENT *pevent);

void OSSemPost( OS_SEM *p_sem, OS_OPT opt, OS_ERR *p_err);

INT8U OSSemQuery( OS_EVENT *pevent, OS_SEM_DATA *p_sem_data);

(4)

void OSSemSet( OS_EVENT *pevent, INT16U cnt, INT8U *perr);

void OSSemSet( OS_SEM *p_sem, OS_SEM_CTR cnt, OS_ERR *p_err);

 

(1) In µC/OS-III, there is no “accept” API since this feature is built into the OSSemPend() by specifying the OS_OPT_PEND_NON_BLOCKING option.

(2) In µC/OS-II, OSSemCreate() returns the address of an OS_EVENT, which is used as the “handle” to the semaphore. In µC/OS-III, the application must allocate storage for an OS_SEM object, which serves the same purpose as the OS_EVENT. The benefit in µC/OS-III is that it is not necessary to predetermine the number of semaphores at compile time.

(3) µC/OS-III returns additional information when a semaphore is signaled. The ISR or task that signals the semaphore takes a snapshot of the current timestamp and stores this in the OS_SEM object signaled. The receiver of the signal therefore knows when the signal was sent.

(4) µC/OS-III does not provide query services, as they were rarely used.