T-Kernel Specification (1.B0.02)

4.2. TASK-DEPENDENT SYNCHRONIZATION FUNCTIONS 67
#define TTW_EV4 0x00080000 /* Wait for task event #4 */
#define TTW_EV5 0x00100000 /* Wait for task event #5 */
#define TTW_EV6 0x00200000 /* Wait for task event #6 */
#define TTW_EV7 0x00400000 /* Wait for task event #7 */
#define TTW_EV8 0x00800000 /* Wait for task event #8 */
#define TTX_SVC 0x80000000 /* Extended SVC disabled */
TTX SVC is a special designation disabling not task wait but the calling of an extended SVC. If TTX SVC
is designated when a task attempts to call an extended SVC, E DISWAI is returned without calling the
extended SVC. This designation does not have the effect of terminating an already called extended SVC.
A tskwait value of 0 means the task has not entered WAIT state (or the wait was released). If tskwait
is not 0, this means the task is in WAIT state for a cause other than those disabled in waitmask.
When a task wait is cleared by tk dis wai or the task is prevented from entering WAIT state while this
system call is in effect, E DISWAI is returned. When a system call for which there is the possibility of
entering a WAIT state is invoked during wait disabled state, E DISWAI is returned even if the processing
could be performed without waiting.
For example, even if message buffer space is available when tk snd mbf is called and message buffer
sending is possible without entering a WAIT state, E DISWAI is returned and the message is not sent.
A wait disable set while an extended SVC is executing will be cleared automatically upon return from
the extended SVC to its caller. It is automatically cleared also when an extended SVC is called, reverting
to the original setting upon return from the extended SVC. A wait disable setting is cleared also when
the task reverts to DORMANT state. The setting made while a task is in DORMANT state, however,
is valid and the wait disable is applied the next time the task is started.
In the case of semaphores and most other objects, TA NODISWAI can be designated when the object is
created. An object created with TA NODISWAI designated cannot have waits disabled, and rejects any
wait disable attempt by tk dis wai.
The invoking task can be designated by setting tskid = TSK SELF = 0. Note, however, that when a
system call is issued from a task-independent portion and tskid = TSK SELF = 0 is designated, error
code E ID is returned.
[Additional Notes]
The wait disable function is provided for preventing execution of an extended SVC handler and is for
use mainly (though not exclusively) in break functions.
Wait disable in the case of a rendezvous is more complex than other cases. Essentially, wait disabled
state is detected based on a change in the rendezvous wait state, then the wait is released. Some specific
examples are given here.
When waiting by TTW CAL is not disabled but TTW RDV waits are disabled, a task enters into wait on
rendezvous call state; but when the rendezvous is accepted and a wait for rendezvous completion would
normally begin, the wait is released and E DISWAI is returned. At this time a message is sent to the
receiving task, the receiving task declares acceptance of the message and the task goes to rendezvous
established state. Only when the accepting task replies (tk rpl rdv) does it become clear that there
is no other task in the rendezvous, and error code E OBJ is returned. Wait disable applies also when a
rendezvous is forwarded. In that case the attribute of the destination rendezvous port applies. That is,
if the TA NODISWAI attribute is designated for the destination port, wait disable is rejected. If TTW CAL
wait is disabled after going to wait for rendezvous completion state, and a rendezvous is forwarded in
that state, the state goes to WAIT on rendezvous call as a result of the forwarding, so wait is disabled
by the TTW CAL designation. In that case E DISWAI is returned to both the rendezvous calling task
(tk cal por) and forwarding task (tk fwd por).
Copyright c○ 2002, 2003 by T-Engine Forum
T-Kernel 1.B0.02