Semaphores API Changes

Owned by Former user (Deleted)
Last updated: Mar 23, 2021 by WES Admin
3 min read

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.