twai_sem

Outline

Acquire semaphore resource (with timeout).

C format

 ER      twai_sem (ID semid, TMO tmout);

Parameter(s)

I/O	Parameter	Description
I	ID semid;	ID number of the semaphore from which resource is acquired.
I	TMO tmout;	Specified timeout (unit:millisecond). TMO_FEVR: Waiting forever. TMO_POL: Polling. Value: Specified timeout.

Explanation

This service call acquires a resource from the semaphore specified by parameter semid (subtracts 0x1 from the semaphore counter).

If no resources are acquired from the target semaphore when service call is issued this (no available resources exist), this service call does not acquire resources but queues the invoking task to the target semaphore wait queue and moves it from the RUNNING state to the WAITING state with timeout (resource acquisition wait state).

The WAITING state for a semaphore resource is cancelled in the following cases, and then moved to the READY state.

WAITING State for a Semaphore Resource Cancel Operation	Return Value
The resource was returned to the target semaphore as a result of issuing sig_sem.	E_OK
The resource was returned to the target semaphore as a result of issuing isig_sem.	E_OK
Forced release from waiting (accept rel_wai while waiting).	E_RLWAI
Forced release from waiting (accept irel_wai while waiting).	E_RLWAI
Polling failure or timeout.	E_TMOUT

Note 1 Invoking tasks are queued to the target semaphore wait queue in the order defined during configuration (FIFO order or priority order).

Note 2 TMO_FEVR is specified for wait time tmout, processing equivalent to wai_sem will be executed. When TMO_POL is specified, processing equivalent to pol_sem /ipol_sem will be executed.

Return value

Macro	Value	Description
E_OK	0	Normal completion.
E_PAR	-17	Parameter error. - tmout < TMO_FEVR
E_ID	-18	Invalid ID number. - semid < 0x0 - semid > Maximum ID number
E_CTX	-25	Context error. - This service call was issued from a non-task. - This service call was issued in the CPU locked state. - This service call was issued in the dispatching disabled state.
E_NOEXS	-42	Non-existent object. - Specified semaphore is not registered.
E_RLWAI	-49	Forced release from the WAITING state. - Accept rel_wai/irel_wai while waiting.
E_TMOUT	-50	Timeout. - Polling failure or timeout.