T-Kernel Specification (1.B0.02)

4.4. SYNCHRONIZATION AND COMMUNICATION FUNCTIONS 83
tk wai sem
Wait on Semaphore
[C Language Interface]
ER ercd = tk_wai_sem ( ID semid, INT cnt, TMO tmout ) ;
[Parameters]
ID semid Semaphore ID
INT cnt Resource request count
TMO tmout Timeout designation
[Return Parameters]
ER ercd Error code
[Error Codes]
E OK Normal completion
E ID Invalid ID number (semid is invalid or cannot be used)
E NOEXS Object does not exist (the semaphore designated in semid does not exist)
E PAR Parameter error (tmout ≤ (−2), cnt ≤ 0)
E DLT The object being waited for was deleted (the designated semaphore was deleted while
waiting)
E RLWAI Wait state released (tk rel wai received in wait state)
E DISWAI Wait released by wait disabled state
E TMOUT Polling failed or timeout
E CTX Context error (issued from task-independent portion or in dispatch disabled state)
[Description]
Gets from the semaphore designated in semid the number of resources indicated in cnt. If the requested
resources can be allocated, the task issuing this system call does not enter WAIT state but continues
executing. In this case the semaphore count (semcnt) is decreased by the size of cnt. If the resources
are not available, the task issuing this system call enters WAIT state, and is put in the queue of tasks
waiting for the semaphore. The semaphore count (semcnt) for this semaphore does not change in this
case.
A maximum wait time (timeout) can be set in tmout. If the tmout time elapses before the wait release
condition is met (tk sig sem is not executed), the system call terminates, returning timeout error code
E TMOUT.
Only positive values can be set in tmout. The time base for tmout (time unit) is the same as that for
system time (= 1 ms).
When TMO POL = 0 is set in tmout, this means 0 was designated as the timeout value, and E TMOUT is
returned without entering WAIT state even if no resources are acquired.
Copyright c○ 2002, 2003 by T-Engine Forum
T-Kernel 1.B0.02