Outline

Acquire semaphore resource (with timeout).

C format

ER twai_sem ( ID semid, TMO tmout );

Assembly format

MOVW BC, #tmout_lo MOVW DE, #tmout_hi MOV A, #semid CALL !!_twai_sem

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: ticks). 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 a resource could not be acquired from the target semaphore (semaphore counter is set to 0x0) when this service call is issued, the counter manipulation processing is not performed but the invoking task is queued to the target semaphore wait queue in the order of resource acquisition request (FIFO order).

As a result, the invoking task is unlinked from the ready queue and is moved from the RUNNING state to the WAITING state (waiting state for a semaphore resource).

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 When 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 will be executed.

Return value

Macro	Value	Description
E_OK	0	Normal completion.
E_RLWAI	-49	Forced release from waiting (accept rel_wai/irel_wai while waiting).
E_TMOUT	-50	Polling failure or timeout.