SEM_ID taskReleaseSem;

void myTimedFunc(void)
{
    semGive(taskReleaseSem);
}

void myTaskFunc(int tickParameter) // The clock tick passes a constant
{
    for(;;) // Pick your favorite forever method
    {
        // Wait for the semaphore to be given
        semTake(taskReleaseSem);
        // Your periodic stuff
    }
}

void initTimedFunc(void)
{
    // Create a semaphore to release the timed task
    taskReleaseSem = semBCreate(SEM_Q_PRIORITY,SEM_EMPTY);

    // Set the aux xloxk to the desired rate
    sysAuxClkRateSet(20);

    // Spawn the task that does the work
    taskSpawn(
         "timed",           /* name of new task (stored at pStackBase) */
         100,                /* priority of new task */
         0,                    /* task option word */
         4096,               /* size (bytes) of stack needed plus name */
         myTaskFunc,   /* entry point of new task */
         0,                    /* 1st of 10 req'd task args to pass to func */
         0, 0, 0, 0, 0, 0, 0, 0, 0
         )

    // Now connect the timer function to the aux clock
    sysAuxClkConnect(myTimedFunc,0);
    // And switch it on
    sysAuxClkEnable();
}