peventis a pointer to the queue where the message is to be deposited into. This pointer is returned to your application when the queue is created (see OSQCreate()).

msg is the actual message sent to the task. msg is a pointer size variable and is application specific. You MUST never post a NULL pointer.

Returned Value

OSQPostFront() returns one of these two error codes

1)OS_NO_ERR, if the message was deposited in the queue

2)OS_Q_FULL, if the queue is already full

Notes/Warnings

Queues must be created before they are used.

Example

.

.

}

}

OSQQuery()

INT8U OSQQuery(OS_EVENT *pevent, OS_Q_DATA *pdata);

OSQQuery() is used to obtain information about a message queue. Your application must allocate an OS_Q_DATA data structure which will be used to receive data from the event control block of the message queue. OSQQuery() allows you to determine whether any task is waiting for message(s) at the queue, how many tasks are waiting (by counting the number of 1s in the .OSEventTbl[] field, how many messages are in the queue, what the message queue size is, and examine the contents of the next message that would be returned if there is at least one message in the queue. You can use the table OSNBitsTbl[] to find out how many ones are set in a given byte. Note that the size of .OSEventTbl[] is established by the #define constant OS_EVENT_TBL_SIZE (see ).

Arguments

pevent is a pointer to the message queue. This pointer is returned to your application when the queue is created (see

OSQCreate()).

pdata is a pointer to a data structure of type OS_Q_DATA which contains the following fields.

Returned Value

OSQQuery() returns one of these two error codes:

1)OS_NO_ERR, if the call was successful

2)OS_ERR_EVENT_TYPE, if you didn’t pass a pointer to a message queue

Notes/Warnings

Message queues must be created before they are used.

Example

In this example, we check the contents of the message queue to see how many tasks are waiting for it.

OS_EVENT *CommQ;

pdata = pdata; for (;;) {

.

.

err = OSQQuery(CommQ, &qdata); if (err == OS_NO_ERR) {

nwait = 0; /* Count # tasks waiting on queue */ if (qdata.OSEventGrp != 0x00) {

for (i = 0; i < OS_EVENT_TBL_SIZE; i++) { nwait += OSNBitsTbl[qdata.OSEventTbl[i]];

}

}

}

.

.

}

}

OSSchedLock()

void OSSchedLock(void);

OSSchedLock() is used to prevent task rescheduling until its counterpart, OSSchedUnlock(), is called. The task which calls OSSchedLock() keeps control of the CPU even though other higher priority tasks are ready to run. However, interrupts will still be recognized and serviced (assuming interrupts are enabled). OSSchedLock() and OSSchedUnlock() must be used in pair. µC/OS-II allows OSSchedLock() to be nested up to 254 levels deep. Scheduling is enabled when an equal number of OSSchedUnlock() calls have been made.

Arguments

NONE

Returned Value

NONE

Notes/Warnings

After calling OSSchedLock(), you application must not make any system call which will suspend execution of the current task i.e., your application cannot call OSTimeDly(), OSTimeDlyHMSM(), OSSemPend(), OSMboxPend() or OSQPend(). Since the scheduler is locked out, no other task will be allowed to run and your system will lock up.

Example

}

}

OSSchedUnlock()

void OSSchedUnlock(void);

OSSchedUnlock() is used to re -enable task scheduling. OSSchedUnlock() is used with OSSchedLock() in pair. Scheduling is enabled when an equal number of OSSchedUnlock() as OSSchedLock() have been made.

Arguments

NONE

Returned Value

NONE

Notes/Warnings

After calling OSSchedLock(), you application must not make any system call which will suspend execution of the current task i.e., your application cannot call OSTimeDly(), OSTimeDlyHMSM(), OSSemPend(), OSMboxPend() or OSQPend(). Since the scheduler is locked out, no other task will be allowed to run and your system will lock up.

Example