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uC/OS-II Timers

uC/OS-II Timers

Jul 08, 2013

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 

 network.

To run the 00-uc_timers sample application, program your 

 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.

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.

  • 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.