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Description

Tasks must be created in order for µC/OS-III to recognize them as tasks. You create a task by calling OSTaskCreate() and by providing arguments specifying to µC/OS-III how the task will be managed. Tasks are always created in the ready-to-run state.

Tasks can be created either prior to the start of multitasking (i.e., before calling OSStart()), or by a running task. A task cannot be created by an ISR. A task must either be written as an infinite loop, or delete itself once completed. If the task code returns by mistake, µC/OS-III will terminate the task by calling OSTaskDel((OS_TCB *)0, &err)). At Micrium, we like the “while (DEF_ON)” to implement infinite loops because, by convention, we use a while loop when we don’t know how many iterations a loop will do. This is the case of an infinite loop. We prefer to use for loops when we know how many iterations a loop will do.

Files

os.h/os_task.c

Prototype

Task as an infinite loop:

Run to completion task:

Arguments

p_tcb

is a pointer to the task’s OS_TCB to use. It is assumed that storage for the TCB of the task will be allocated by the user code. You can declare a “global” variable as follows, and pass a pointer to this variable to OSTaskCreate():

...

If OS_SAFETY_CRITICAL_IEC61508 is defined: you called this after calling OSSafetyCriticalStart() and thus you are no longer allowed to create additional kernel objects.

Returned Value

None

Notes/Warnings

• The stack must be declared with the CPU_STK type.
• A task must always invoke one of the services provided by µC/OS-III to wait for time to expire, suspend the task, or wait on an object (wait on a message queue, event flag, mutex, semaphore, a signal or a message to be sent directly to the task). This allows other tasks to gain control of the CPU.
• You should not use task priorities 0, 1, OS_CFG_PRIO_MAX-2 and OS_CFG_PRIO_MAX-1 because they are reserved for use by µC/OS-III.

Example Usage

OSTaskCreate() can be called from main() (in C), or a previously created task.