T-Kernel Specification (1.B0.02)

54 CHAPTER 4. T-KERNEL/OS FUNCTIONS
tk slp tsk
Sleep Task
[C Language Interface]
ER ercd = tk_slp_tsk ( TMO tmout ) ;
[Parameters]
TMO tmout Timeout designation
[Return Parameters]
ER ercd Error code
[Error Codes]
E OK
E PAR
E RLWAI
E DISWAI
E TMOUT
E CTX
Normal completion
Parameter error (tmout ≤ (−2))
Wait state released (tk rel wai received in wait state)
Wait released by wait disabled state
Polling failed or timeout
Context error (issued from task-independent portion or in dispatch disabled state)
[Description]
Changes the state of the invoking task from RUN state to sleep state (WAIT for tk wup tsk).
If tk wup tsk is issued for the invoking task before the time designated in tmout has elapsed, this system
call completes normally. If timeout occurs before tk wup tsk is issued, error code E TMOUT is returned.
Designating tmout = TMO FEVR = (−1) means endless wait. In this case, the task stays in waiting state
until tk wup tsk is issued.
[Additional Notes]
Since tk slp tsk is a system call that puts the invoking task into a wait state, tk slp tsk can never
be nested. It is possible, however, for another task to issue tk sus tsk for a task that was put in a wait
state by tk slp tsk. In this case the task goes to WAIT-SUSPEND state.
For simply delaying a task, tk dly tsk should be used rather than tk slp tsk.
The task sleep function is intended for use by applications and as a rule should not be used by middleware.
The reason is that attempting to achieve synchronization by putting a task to sleep in two or more
places would cause confusion, leading to misoperation. For example, if sleep were used by both an
application and middleware for synchronization, a wakeup request might arise in the application while
middleware has the task sleeping. In such a situation, normal operation would not be possible in either
the application or middleware. Proper task synchronization is not possible because it is not clear where
the wait for wakeup originated. Task sleep is often used as a simple means of task synchronization.
Applications should be able to use it freely, which means as a rule it should not be used by middleware.
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T-Kernel 1.B0.02