Outline

Acquire semaphore resource (waiting forever).

C format

ER wai_sem ( ID semid );

Assembly format

MOV A, #semid CALL !!_wai_sem

Parameter(s)

I/O	Parameter	Description
I	ID semid;	ID number of the semaphore from which resource is acquired.

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 state).

Waiting State for a Semaphore State 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

Return value

Macro	Value	Description
E_OK	0	Normal completion.
E_RLWAI	-49	Forced release from waiting (accept rel_wai/irel_wai while waiting).