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Chapter 3
L3-7(2)
The task then sends a message to another task using the message queue AppQ.
In this case, the example shows a fixed message “1,” but the message could
have consisted of the address of a buffer, the address of a function, or whatever
would need to be sent.
L3-7(3)
The task then waits on the mutual exclusion semaphore since it needs to access
a shared resource with another task. If the resource is already owned by
another task, AppTask1() will wait forever for the mutex to be released by its
current owner. The forever wait is specified by passing 0 as the second
argument of the call.
L3-7(4)
When OSMutexPend() returns, the task owns the resource and can therefore
access the shared resource. The shared resource may be a variable, an array, a
data structure, an I/O device, etc.
L3-7(5)
When the task is done with the shared resource, it must call OSMutexPost() to
release the mutex.
static void AppTask2 (void *p_arg)
{
OS_ERR err;
void *p_msg;
OS_MSG_SIZE msg_size;
CPU_TS ts;
CPU_TS ts_delta;
p_arg = p_arg;
while (1) {
p_msg = OSQPend((OS_Q *)&AppQ,
(OS_MSG_SIZE *)&msg_size,
(OS_TICK )0,
(OS_OPT )OS_OPT_PEND_BLOCKING,
(CPU_TS *)&ts,
(OS_ERR *)&err);
ts_delta = OS_TS_GET() – ts;
/* Process message received */
(1)
(2)
(3)
}
}
Listing 3-8 APP.C (5th Part)
66
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