Semaphores in µC/OS-III

Table C-13 shows the difference in API for semaphore management.

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);

Table C-13 Semaphore Management API

TC-13(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.

TC-13(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.

TC-13(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.

TC-13(4) µC/OS-III does not provide query services, as they were rarely used.