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This section refers to the following sample application(s):

  • 00-uc_timers

The Timers section details the modifications done to timers implementation of uC/OS-II to ensure ultra low-power operation. It also highlights the two different approaches of delaying the execution of one of your tasks. We recommend you go over the Timers section before reading this section.

The 00-uc_timers Sample Application

The 00-uc_timers sample application creates two independent tasks (called timerATask and timerBTask). Each of these tasks continuously waits, and prints the letter "A" or "B" over the CLI.

This application runs without your intervention, and does not connect to the 

Include Page
_def_sm
_def_sm
 network.

To run the 00-uc_timers sample application, program your 

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_def_mote
_def_mote
 and open a terminal client on the CLI serial port. After the banner, you will see a continuous stream of "A" and "B" characters, indicating that the uC/OS-II kernel is constantly switching execution between the two tasks.

No Format
uc_timers app, ver 1.0.0.2
SmartMeshIP stack, ver 1.2.1.5
ABABABABABABABABABABABABABABABABABABABABAABABABABABABABABABABABABA
BABABABABABABABABAABABABABABABABABABABABABABABABABABABABABABAABABA
BABABABABABABABABABABABABABABABABABABAABABABABABABABABABABABABABAB
ABABABABABABAABABABABABABABABABABABABABABABABABABABABABAABABABABAB
ABABABABABABABABABABABABABABABABAABABABABABABABABABABABABABABABABA
BABABABABAABABABABABABABABABABABABABABABABABABABABABAABABABABABABA
BABABABABABABABABABABABABABAABABABABABABABABABABABABABABABABABABAB

While both tasks perform similar functions, the way the delay is implemented is different:

  • timerATask calls OSTimeDly() as part of its own task context. This causes the uC/OS-II scheduler to pause the execution of the task for the specified amount of time.

    Note

    As detailed in the Timers section, when the OSTimeDly() is executing, a semaphore is used. You need to account for this when provisioning for the number of Event Control Blocks (ECBs) your application is using.

  • In its initialization section, the timerBTask creates a timer using the OSTmrCreate() function. This timer is set to fire periodically, and call the timerB_cb() function each time it does. The only thing this callback function does is post a semaphore. In its main loop, the the timerBTask pends on that semaphore at each iteration, causing it to loop at the required rate.

    Tip

    This implementation is an example of the "best practice" rules highlighted in the Timers section, i.e. the body of the timerB_cb() callback function executes quickly, and does not reserve a large amount of memory on the stack space of the "timer task".