title: How to use timer's OSTmrCreate to implement task scheduling with MicroC/OS II?
body: <p>I got 2 tasks in MicroC to simulate a moving vehicle: ControlTask and VehicleTask. Now my project should replace the context switch with a timer for more appropriate timing but I can't seem to get it done. The program now uses the statement <code>OSTimeDlyHMSM</code> to implement periods but instead soft timers should be used with semaphores. OSTmrCreate in C/OS-II ReferenceManual (Chapter 16). I can start a timer then I can place it in the start code but I'm failing to call the timer and sync properly between the two tasks replacing the <code>OSTimeDlyHMSM</code> with a timer. I think my solution is getting more complicated than neccesary because I might not understand all details e.g. why I need semaphores and why it's more exact with a timer than the builtin <code>OSTimeDlyHMSM</code>. My complete effort this far looks like the following:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include "system.h"
  #include "includes.h"
  #include "altera_avalon_pio_regs.h"
  #include "sys/alt_irq.h"
  #include "sys/alt_alarm.h"
  
  #define DEBUG 1
  
  #define HW_TIMER_PERIOD 100 /* 100ms */
  
  /* Button Patterns */
  
  #define GAS_PEDAL_FLAG      0x08
  #define BRAKE_PEDAL_FLAG    0x04
  #define CRUISE_CONTROL_FLAG 0x02
  /* Switch Patterns */
  
  #define TOP_GEAR_FLAG       0x00000002
  #define ENGINE_FLAG         0x00000001
  
  /* LED Patterns */
  
  #define LED_RED_0 0x00000001 // Engine
  #define LED_RED_1 0x00000002 // Top Gear
  
  #define LED_GREEN_0 0x0001 // Cruise Control activated
  #define LED_GREEN_2 0x0002 // Cruise Control Button
  #define LED_GREEN_4 0x0010 // Brake Pedal
  #define LED_GREEN_6 0x0040 // Gas Pedal
  
  /*
   * Definition of Tasks
   */
  
  #define TASK_STACKSIZE 2048
  
  OS_STK StartTask_Stack[TASK_STACKSIZE]; 
  OS_STK ControlTask_Stack[TASK_STACKSIZE]; 
  OS_STK VehicleTask_Stack[TASK_STACKSIZE];
  
  // Task Priorities
  
  #define STARTTASK_PRIO     5
  #define VEHICLETASK_PRIO  10
  #define CONTROLTASK_PRIO  12
  
  // Task Periods
  
  #define CONTROL_PERIOD  300
  #define VEHICLE_PERIOD  300
  
  /*
   * Definition of Kernel Objects 
   */
  
  // Mailboxes
  OS_EVENT *Mbox_Throttle;
  OS_EVENT *Mbox_Velocity;
  
  
  // Semaphores
  OS_EVENT *aSemaphore;
  // SW-Timer
  OS_TMR *SWTimer;
  OS_TMR *SWTimer1;
  BOOLEAN status;
  /*
   * Types
   */
  enum active {on, off};
  
  enum active gas_pedal = off;
  enum active brake_pedal = off;
  enum active top_gear = off;
  enum active engine = off;
  enum active cruise_control = off; 
  
  /*
   * Global variables
   */
  int delay; // Delay of HW-timer 
  INT16U led_green = 0; // Green LEDs
  INT32U led_red = 0;   // Red LEDs
  
  int sharedMemory=1;
  
  void ContextSwitch()
  {  
      printf("ContextSwitch!\n"); 
      sharedMemory=sharedMemory*-1;
  }
  int buttons_pressed(void)
  {
    return ~IORD_ALTERA_AVALON_PIO_DATA(DE2_PIO_KEYS4_BASE);    
  }
  
  int switches_pressed(void)
  {
    return IORD_ALTERA_AVALON_PIO_DATA(DE2_PIO_TOGGLES18_BASE);    
  }
  
  /*
   * ISR for HW Timer
   */
  alt_u32 alarm_handler(void* context)
  {
    OSTmrSignal(); /* Signals a 'tick' to the SW timers */
  
    return delay;
  }
  
  static int b2sLUT[] = {0x40, //0
                   0x79, //1
                   0x24, //2
                   0x30, //3
                   0x19, //4
                   0x12, //5
                   0x02, //6
                   0x78, //7
                   0x00, //8
                   0x18, //9
                   0x3F, //-
  };
  
  /*
   * convert int to seven segment display format
   */
  int int2seven(int inval){
      return b2sLUT[inval];
  }
  
  /*
   * output current velocity on the seven segement display
   */
  void show_velocity_on_sevenseg(INT8S velocity){
    int tmp = velocity;
    int out;
    INT8U out_high = 0;
    INT8U out_low = 0;
    INT8U out_sign = 0;
  
    if(velocity &lt; 0){
       out_sign = int2seven(10);
       tmp *= -1;
    }else{
       out_sign = int2seven(0);
    }
  
    out_high = int2seven(tmp / 10);
    out_low = int2seven(tmp - (tmp/10) * 10);
  
    out = int2seven(0) &lt;&lt; 21 |
              out_sign &lt;&lt; 14 |
              out_high &lt;&lt; 7  |
              out_low;
    IOWR_ALTERA_AVALON_PIO_DATA(DE2_PIO_HEX_LOW28_BASE,out);
  }
  
  /*
   * shows the target velocity on the seven segment display (HEX5, HEX4)
   * when the cruise control is activated (0 otherwise)
   */
  void show_target_velocity(INT8U target_vel)
  {
  }
  
  /*
   * indicates the position of the vehicle on the track with the four leftmost red LEDs
   * LEDR17: [0m, 400m)
   * LEDR16: [400m, 800m)
   * LEDR15: [800m, 1200m)
   * LEDR14: [1200m, 1600m)
   * LEDR13: [1600m, 2000m)
   * LEDR12: [2000m, 2400m]
   */
  void show_position(INT16U position)
  {
  }
  
  /*
   * The function 'adjust_position()' adjusts the position depending on the
   * acceleration and velocity.
   */
   INT16U adjust_position(INT16U position, INT16S velocity,
                          INT8S acceleration, INT16U time_interval)
  {
    INT16S new_position = position + velocity * time_interval / 1000
      + acceleration / 2  * (time_interval / 1000) * (time_interval / 1000);
  
    if (new_position &gt; 24000) {
      new_position -= 24000;
    } else if (new_position &lt; 0){
      new_position += 24000;
    }
  
    show_position(new_position);
    return new_position;
  }
  
  /*
   * The function 'adjust_velocity()' adjusts the velocity depending on the
   * acceleration.
   */
  INT16S adjust_velocity(INT16S velocity, INT8S acceleration,  
                 enum active brake_pedal, INT16U time_interval)
  {
    INT16S new_velocity;
    INT8U brake_retardation = 200;
  
    if (brake_pedal == off)
      new_velocity = velocity  + (float) (acceleration * time_interval) / 1000.0;
    else {
      if (brake_retardation * time_interval / 1000 &gt; velocity)
        new_velocity = 0;
      else
        new_velocity = velocity - brake_retardation * time_interval / 1000;
    }
  
    return new_velocity;
  }
  
  /*
   * The task 'VehicleTask' updates the current velocity of the vehicle
   */
  void VehicleTask(void* pdata)
  { 
    INT8U err;  
    void* msg;
    INT8U* throttle; 
    INT8S acceleration;  /* Value between 40 and -20 (4.0 m/s^2 and -2.0 m/s^2) */
    INT8S retardation;   /* Value between 20 and -10 (2.0 m/s^2 and -1.0 m/s^2) */
    INT16U position = 0; /* Value between 0 and 20000 (0.0 m and 2000.0 m)  */
    INT16S velocity = 0; /* Value between -200 and 700 (-20.0 m/s amd 70.0 m/s) */
    INT16S wind_factor;   /* Value between -10 and 20 (2.0 m/s^2 and -1.0 m/s^2) */
  
    printf("Vehicle task created!\n");
  
    while(1)
      {
        err = OSMboxPost(Mbox_Velocity, (void *) &amp;velocity);
  
        OSTimeDlyHMSM(0,0,0,VEHICLE_PERIOD); 
  
        /* Non-blocking read of mailbox: 
         - message in mailbox: update throttle
         - no message:         use old throttle
        */
        msg = OSMboxPend(Mbox_Throttle, 1, &amp;err); 
        if (err == OS_NO_ERR) 
           throttle = (INT8U*) msg;
  
        /* Retardation : Factor of Terrain and Wind Resistance */
        if (velocity &gt; 0)
           wind_factor = velocity * velocity / 10000 + 1;
        else 
           wind_factor = (-1) * velocity * velocity / 10000 + 1;
  
        if (position &lt; 4000) 
           retardation = wind_factor; // even ground
        else if (position &lt; 8000)
            retardation = wind_factor + 15; // traveling uphill
          else if (position &lt; 12000)
              retardation = wind_factor + 25; // traveling steep uphill
            else if (position &lt; 16000)
                retardation = wind_factor; // even ground
              else if (position &lt; 20000)
                  retardation = wind_factor - 10; //traveling downhill
                else
                    retardation = wind_factor - 5 ; // traveling steep downhill
  
        acceleration = *throttle / 2 - retardation;     
        position = adjust_position(position, velocity, acceleration, 300); 
        velocity = adjust_velocity(velocity, acceleration, brake_pedal, 300); 
        printf("Position: %dm\n", position / 10);
        printf("Velocity: %4.1fm/s\n", velocity /10.0);
        printf("Throttle: %dV\n", *throttle / 10);
        show_velocity_on_sevenseg((INT8S) (velocity / 10));
      }
  } 
  
  /*
   * The task 'ControlTask' is the main task of the application. It reacts
   * on sensors and generates responses.
   */
  
  void ControlTask(void* pdata)
  {
    INT8U err;
    INT8U throttle = 40; /* Value between 0 and 80, which is interpreted as between 0.0V and 8.0V */
    void* msg;
    INT16S* current_velocity;
  
    printf("Control Task created!\n");
  
    while(1)
      {
        msg = OSMboxPend(Mbox_Velocity, 0, &amp;err);
        current_velocity = (INT16S*) msg;
  
        err = OSMboxPost(Mbox_Throttle, (void *) &amp;throttle);
  
        OSTimeDlyHMSM(0,0,0, CONTROL_PERIOD);
      }
  }
  
  /* 
   * The task 'StartTask' creates all other tasks kernel objects and
   * deletes itself afterwards.
   */ 
  
  void StartTask(void* pdata)
  {
    INT8U err;
    void* context;
  
    static alt_alarm alarm;     /* Is needed for timer ISR function */
  
    /* Base resolution for SW timer : HW_TIMER_PERIOD ms */
    delay = alt_ticks_per_second() * HW_TIMER_PERIOD / 1000; 
    printf("delay in ticks %d\n", delay);
  
    /* 
     * Create Hardware Timer with a period of 'delay' 
     */
    if (alt_alarm_start (&amp;alarm,
        delay,
        alarm_handler,
        context) &lt; 0)
        {
            printf("No system clock available!n");
        }
  
    /* 
     * Create and start Software Timer 
     */
  
    SWTimer = OSTmrCreate(0,
    CONTROL_PERIOD/(4*OS_TMR_CFG_TICKS_PER_SEC),
    OS_TMR_OPT_PERIODIC,
    ContextSwitch,
    NULL,
    NULL,
    &amp;err);
       if (err == OS_ERR_NONE) {
    /* Timer was created but NOT started */
    printf("SWTimer was created but NOT started \n");
    }
  
    status = OSTmrStart(SWTimer,
      &amp;err);
    if (err == OS_ERR_NONE) {
    /* Timer was started */
      printf("SWTimer was started!\n");
    }
    /*
     * Creation of Kernel Objects
     */
  
    // Mailboxes
    Mbox_Throttle = OSMboxCreate((void*) 0); /* Empty Mailbox - Throttle */
    Mbox_Velocity = OSMboxCreate((void*) 0); /* Empty Mailbox - Velocity */
  
    /*
     * Create statistics task
     */
  
    OSStatInit();
  
    /* 
     * Creating Tasks in the system 
     */
  
  
    err = OSTaskCreateExt(
         ControlTask, // Pointer to task code
         NULL,        // Pointer to argument that is
                      // passed to task
         &amp;ControlTask_Stack[TASK_STACKSIZE-1], // Pointer to top
                               // of task stack
         CONTROLTASK_PRIO,
         CONTROLTASK_PRIO,
         (void *)&amp;ControlTask_Stack[0],
         TASK_STACKSIZE,
         (void *) 0,
         OS_TASK_OPT_STK_CHK);
  
    err = OSTaskCreateExt(
         VehicleTask, // Pointer to task code
         NULL,        // Pointer to argument that is
                      // passed to task
         &amp;VehicleTask_Stack[TASK_STACKSIZE-1], // Pointer to top
                               // of task stack
         VEHICLETASK_PRIO,
         VEHICLETASK_PRIO,
         (void *)&amp;VehicleTask_Stack[0],
         TASK_STACKSIZE,
         (void *) 0,
         OS_TASK_OPT_STK_CHK);
  
    printf("All Tasks and Kernel Objects generated!\n");
  
    /* Task deletes itself */
  
    OSTaskDel(OS_PRIO_SELF);
  }
  
  /*
   *
   * The function 'main' creates only a single task 'StartTask' and starts
   * the OS. All other tasks are started from the task 'StartTask'.
   *
   */
  
  int main(void) {
  
    printf("Cruise Control\n");
    aSemaphore = OSSemCreate(1); // binary semaphore (1 key)  
  
    OSTaskCreateExt(
       StartTask, // Pointer to task code
           NULL,      // Pointer to argument that is
                      // passed to task
           (void *)&amp;StartTask_Stack[TASK_STACKSIZE-1], // Pointer to top
                               // of task stack 
           STARTTASK_PRIO,
           STARTTASK_PRIO,
           (void *)&amp;StartTask_Stack[0],
           TASK_STACKSIZE,
           (void *) 0,  
           OS_TASK_OPT_STK_CHK | OS_TASK_OPT_STK_CLR);
  
    OSStart();
  
    return 0;
  }
  </code></pre>
  
  <p>Running the above program the callback <code>contextswitch</code> is executed but it doesn't yet solve the problem of using timers instead of the builtin yield and how to apply it with semaphores.</p>
  
  <pre><code>Cruise Control
  delay in ticks 100
  SWTimer was created but NOT started 
  SWTimer was started!
  All Tasks and Kernel Objects generated!
  Vehicle task created!
  Control Task created!
  ContextSwitch!
  Position: 0m
  Velocity:  0.5m/s
  Throttle: 4V
  ContextSwitch!
  Position: 0m
  Velocity:  1.0m/s
  Throttle: 4V
  Position: 0m
  Velocity:  1.5m/s
  Throttle: 4V
  ContextSwitch!
  Position: 0m
  Velocity:  2.0m/s
  Throttle: 4V
  ContextSwitch!
  Position: 1m
  Velocity:  2.5m/s
  Throttle: 4V
  ContextSwitch!
  Position: 2m
  Velocity:  3.0m/s
  Throttle: 4V
  ContextSwitch!
  </code></pre>
  
  <h2>Update 141001 15:57 CET</h2>
  
  <p>2 semaphores + 2 timers seem like a good improvement. I hope it can be checked or tested...</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include "system.h"
  #include "includes.h"
  #include "altera_avalon_pio_regs.h"
  #include "sys/alt_irq.h"
  #include "sys/alt_alarm.h"
  
  #define DEBUG 1
  
  #define HW_TIMER_PERIOD 100 /* 100ms */
  
  /* Button Patterns */
  
  #define GAS_PEDAL_FLAG      0x08
  #define BRAKE_PEDAL_FLAG    0x04
  #define CRUISE_CONTROL_FLAG 0x02
  /* Switch Patterns */
  
  #define TOP_GEAR_FLAG       0x00000002
  #define ENGINE_FLAG         0x00000001
  
  /* LED Patterns */
  
  #define LED_RED_0 0x00000001 // Engine
  #define LED_RED_1 0x00000002 // Top Gear
  
  #define LED_GREEN_0 0x0001 // Cruise Control activated
  #define LED_GREEN_2 0x0002 // Cruise Control Button
  #define LED_GREEN_4 0x0010 // Brake Pedal
  #define LED_GREEN_6 0x0040 // Gas Pedal
  
  /*
   * Definition of Tasks
   */
  
  #define TASK_STACKSIZE 2048
  
  OS_STK StartTask_Stack[TASK_STACKSIZE]; 
  OS_STK ControlTask_Stack[TASK_STACKSIZE]; 
  OS_STK VehicleTask_Stack[TASK_STACKSIZE];
  
  // Task Priorities
  
  #define STARTTASK_PRIO     5
  #define VEHICLETASK_PRIO  10
  #define CONTROLTASK_PRIO  12
  
  // Task Periods
  
  #define CONTROL_PERIOD  300
  #define VEHICLE_PERIOD  300
  
  /*
   * Definition of Kernel Objects 
   */
  
  // Mailboxes
  OS_EVENT *Mbox_Throttle;
  OS_EVENT *Mbox_Velocity;
  
  
  // Semaphores
  OS_EVENT *aSemaphore;
  OS_EVENT *aSemaphore2;
  // SW-Timer
  OS_TMR *SWTimer;
  OS_TMR *SWTimer1;
  BOOLEAN status;
  /*
   * Types
   */
  enum active {on, off};
  
  enum active gas_pedal = off;
  enum active brake_pedal = off;
  enum active top_gear = off;
  enum active engine = off;
  enum active cruise_control = off; 
  
  /*
   * Global variables
   */
  int delay; // Delay of HW-timer 
  INT16U led_green = 0; // Green LEDs
  INT32U led_red = 0;   // Red LEDs
  
  int sharedMemory=1;
  void TimerCallback(params)
  {
      // Post to the semaphore to signal that it's time to run the task.
      OSSemPost(aSemaphore); // Releasing the key
  }
  void ContextSwitch()
  {  
      printf("ContextSwitch!\n"); 
      sharedMemory=sharedMemory*-1;
  }
  int buttons_pressed(void)
  {
    return ~IORD_ALTERA_AVALON_PIO_DATA(DE2_PIO_KEYS4_BASE);    
  }
  
  int switches_pressed(void)
  {
    return IORD_ALTERA_AVALON_PIO_DATA(DE2_PIO_TOGGLES18_BASE);    
  }
  
  /*
   * ISR for HW Timer
   */
  alt_u32 alarm_handler(void* context)
  {
    OSTmrSignal(); /* Signals a 'tick' to the SW timers */
  
    return delay;
  }
  
  void release()
  {
    printf("release key!\n");
    //OSSemPost(aSemaphore); // Releasing the key
    OSSemPost(aSemaphore2); // Releasing the key
    printf("released key!\n");
  }
  void release2()
  {
    printf("release2!\n");
    OSSemPost(aSemaphore2); // Releasing the key
    printf("release2!\n");
  }
  
  static int b2sLUT[] = {0x40, //0
                   0x79, //1
                   0x24, //2
                   0x30, //3
                   0x19, //4
                   0x12, //5
                   0x02, //6
                   0x78, //7
                   0x00, //8
                   0x18, //9
                   0x3F, //-
  };
  
  /*
   * convert int to seven segment display format
   */
  int int2seven(int inval){
      return b2sLUT[inval];
  }
  
  /*
   * output current velocity on the seven segement display
   */
  void show_velocity_on_sevenseg(INT8S velocity){
    int tmp = velocity;
    int out;
    INT8U out_high = 0;
    INT8U out_low = 0;
    INT8U out_sign = 0;
  
    if(velocity &lt; 0){
       out_sign = int2seven(10);
       tmp *= -1;
    }else{
       out_sign = int2seven(0);
    }
  
    out_high = int2seven(tmp / 10);
    out_low = int2seven(tmp - (tmp/10) * 10);
  
    out = int2seven(0) &lt;&lt; 21 |
              out_sign &lt;&lt; 14 |
              out_high &lt;&lt; 7  |
              out_low;
    IOWR_ALTERA_AVALON_PIO_DATA(DE2_PIO_HEX_LOW28_BASE,out);
  }
  
  /*
   * shows the target velocity on the seven segment display (HEX5, HEX4)
   * when the cruise control is activated (0 otherwise)
   */
  void show_target_velocity(INT8U target_vel)
  {
  }
  
  /*
   * indicates the position of the vehicle on the track with the four leftmost red LEDs
   * LEDR17: [0m, 400m)
   * LEDR16: [400m, 800m)
   * LEDR15: [800m, 1200m)
   * LEDR14: [1200m, 1600m)
   * LEDR13: [1600m, 2000m)
   * LEDR12: [2000m, 2400m]
   */
  void show_position(INT16U position)
  {
  }
  
  /*
   * The function 'adjust_position()' adjusts the position depending on the
   * acceleration and velocity.
   */
   INT16U adjust_position(INT16U position, INT16S velocity,
                          INT8S acceleration, INT16U time_interval)
  {
    INT16S new_position = position + velocity * time_interval / 1000
      + acceleration / 2  * (time_interval / 1000) * (time_interval / 1000);
  
    if (new_position &gt; 24000) {
      new_position -= 24000;
    } else if (new_position &lt; 0){
      new_position += 24000;
    }
  
    show_position(new_position);
    return new_position;
  }
  
  /*
   * The function 'adjust_velocity()' adjusts the velocity depending on the
   * acceleration.
   */
  INT16S adjust_velocity(INT16S velocity, INT8S acceleration,  
                 enum active brake_pedal, INT16U time_interval)
  {
    INT16S new_velocity;
    INT8U brake_retardation = 200;
  
    if (brake_pedal == off)
      new_velocity = velocity  + (float) (acceleration * time_interval) / 1000.0;
    else {
      if (brake_retardation * time_interval / 1000 &gt; velocity)
        new_velocity = 0;
      else
        new_velocity = velocity - brake_retardation * time_interval / 1000;
    }
  
    return new_velocity;
  }
  
  /*
   * The task 'VehicleTask' updates the current velocity of the vehicle
   */
  void VehicleTask(void* pdata)
  { 
    INT8U err;  
    void* msg;
    INT8U* throttle; 
    INT8S acceleration;  /* Value between 40 and -20 (4.0 m/s^2 and -2.0 m/s^2) */
    INT8S retardation;   /* Value between 20 and -10 (2.0 m/s^2 and -1.0 m/s^2) */
    INT16U position = 0; /* Value between 0 and 20000 (0.0 m and 2000.0 m)  */
    INT16S velocity = 0; /* Value between -200 and 700 (-20.0 m/s amd 70.0 m/s) */
    INT16S wind_factor;   /* Value between -10 and 20 (2.0 m/s^2 and -1.0 m/s^2) */
  
    printf("Vehicle task created!\n");
  // Create a semaphore to represent the "it's time to run" event.
      // Initialize the semaphore count to zero because it's not time
      // to run yet.
  
      // Create a periodic software timer which calls TimerCallback()
      // when it expires.
  
      /* 
     * Create and start Software Timer 
     */
  
    SWTimer1 = OSTmrCreate(0,
    CONTROL_PERIOD/(4*OS_TMR_CFG_TICKS_PER_SEC),
    OS_TMR_OPT_PERIODIC,
    TimerCallback,
    NULL,
    NULL,
    &amp;err);
       if (err == OS_ERR_NONE) {
    /* Timer was created but NOT started */
    printf("SWTimer1 was created but NOT started \n");
    }
  
    status = OSTmrStart(SWTimer1,
      &amp;err);
    if (err == OS_ERR_NONE) {
    /* Timer was started */
      printf("SWTimer1 was started!\n");
    }
  
    while(1)
      {
        OSSemPend(aSemaphore, 0, &amp;err); // Trying to access the key   
        err = OSMboxPost(Mbox_Velocity, (void *) &amp;velocity);
  
        //OSTimeDlyHMSM(0,0,0,VEHICLE_PERIOD); 
  
        /* Non-blocking read of mailbox: 
         - message in mailbox: update throttle
         - no message:         use old throttle
        */
        msg = OSMboxPend(Mbox_Throttle, 1, &amp;err); 
        if (err == OS_NO_ERR) 
           throttle = (INT8U*) msg;
  
        /* Retardation : Factor of Terrain and Wind Resistance */
        if (velocity &gt; 0)
           wind_factor = velocity * velocity / 10000 + 1;
        else 
           wind_factor = (-1) * velocity * velocity / 10000 + 1;
  
        if (position &lt; 4000) 
           retardation = wind_factor; // even ground
        else if (position &lt; 8000)
            retardation = wind_factor + 15; // traveling uphill
          else if (position &lt; 12000)
              retardation = wind_factor + 25; // traveling steep uphill
            else if (position &lt; 16000)
                retardation = wind_factor; // even ground
              else if (position &lt; 20000)
                  retardation = wind_factor - 10; //traveling downhill
                else
                    retardation = wind_factor - 5 ; // traveling steep downhill
  
        acceleration = *throttle / 2 - retardation;     
        position = adjust_position(position, velocity, acceleration, 300); 
        velocity = adjust_velocity(velocity, acceleration, brake_pedal, 300); 
        printf("Position: %dm\n", position / 10);
        printf("Velocity: %4.1fm/s\n", velocity /10.0);
        printf("Throttle: %dV\n", *throttle / 10);
        show_velocity_on_sevenseg((INT8S) (velocity / 10));
        //OSSemPost(aSemaphore); // Releasing the key
  
      }
  } 
  
  /*
   * The task 'ControlTask' is the main task of the application. It reacts
   * on sensors and generates responses.
   */
  
  void ControlTask(void* pdata)
  {
    INT8U err;
    INT8U throttle = 40; /* Value between 0 and 80, which is interpreted as between 0.0V and 8.0V */
    void* msg;
    INT16S* current_velocity;
  
    printf("Control Task created!\n");
  
    while(1)
      {
        OSSemPend(aSemaphore2, 0, &amp;err); // Trying to access the key   
        msg = OSMboxPend(Mbox_Velocity, 0, &amp;err);
        current_velocity = (INT16S*) msg;
        printf("Control Task!\n");
        err = OSMboxPost(Mbox_Throttle, (void *) &amp;throttle);
        //OSSemPost(aSemaphore2); // Releasing the key
        //OSTimeDlyHMSM(0,0,0, CONTROL_PERIOD);
      }
  }
  
  /* 
   * The task 'StartTask' creates all other tasks kernel objects and
   * deletes itself afterwards.
   */ 
  
  void StartTask(void* pdata)
  {
    INT8U err;
    void* context;
  
    static alt_alarm alarm;     /* Is needed for timer ISR function */
  
    /* Base resolution for SW timer : HW_TIMER_PERIOD ms */
    delay = alt_ticks_per_second() * HW_TIMER_PERIOD / 1000; 
    printf("delay in ticks %d\n", delay);
  
    /* 
     * Create Hardware Timer with a period of 'delay' 
     */
    if (alt_alarm_start (&amp;alarm,
        delay,
        alarm_handler,
        context) &lt; 0)
        {
            printf("No system clock available!n");
        }
  
    /* 
     * Create and start Software Timer 
     */
  
    SWTimer = OSTmrCreate(0,
    CONTROL_PERIOD/(4*OS_TMR_CFG_TICKS_PER_SEC),
    OS_TMR_OPT_PERIODIC,
    release,
    NULL,
    NULL,
    &amp;err);
       if (err == OS_ERR_NONE) {
    /* Timer was created but NOT started */
    printf("SWTimer was created but NOT started \n");
    }
  
    status = OSTmrStart(SWTimer,
      &amp;err);
    if (err == OS_ERR_NONE) {
    /* Timer was started */
      printf("SWTimer was started!\n");
    }
    /*
     * Creation of Kernel Objects
     */
  
    // Mailboxes
    Mbox_Throttle = OSMboxCreate((void*) 0); /* Empty Mailbox - Throttle */
    Mbox_Velocity = OSMboxCreate((void*) 0); /* Empty Mailbox - Velocity */
  
    /*
     * Create statistics task
     */
  
    OSStatInit();
  
    /* 
     * Creating Tasks in the system 
     */
  
  
    err = OSTaskCreateExt(
         ControlTask, // Pointer to task code
         NULL,        // Pointer to argument that is
                      // passed to task
         &amp;ControlTask_Stack[TASK_STACKSIZE-1], // Pointer to top
                               // of task stack
         CONTROLTASK_PRIO,
         CONTROLTASK_PRIO,
         (void *)&amp;ControlTask_Stack[0],
         TASK_STACKSIZE,
         (void *) 0,
         OS_TASK_OPT_STK_CHK);
  
    err = OSTaskCreateExt(
         VehicleTask, // Pointer to task code
         NULL,        // Pointer to argument that is
                      // passed to task
         &amp;VehicleTask_Stack[TASK_STACKSIZE-1], // Pointer to top
                               // of task stack
         VEHICLETASK_PRIO,
         VEHICLETASK_PRIO,
         (void *)&amp;VehicleTask_Stack[0],
         TASK_STACKSIZE,
         (void *) 0,
         OS_TASK_OPT_STK_CHK);
  
    printf("All Tasks and Kernel Objects generated!\n");
  
    /* Task deletes itself */
  
    OSTaskDel(OS_PRIO_SELF);
  }
  
  /*
   *
   * The function 'main' creates only a single task 'StartTask' and starts
   * the OS. All other tasks are started from the task 'StartTask'.
   *
   */
  
  int main(void) {
  
    printf("Cruise Control 2014\n");
    aSemaphore = OSSemCreate(1); // binary semaphore (1 key)  
    aSemaphore2 = OSSemCreate(0); // binary semaphore (1 key)    
    OSTaskCreateExt(
       StartTask, // Pointer to task code
           NULL,      // Pointer to argument that is
                      // passed to task
           (void *)&amp;StartTask_Stack[TASK_STACKSIZE-1], // Pointer to top
                               // of task stack 
           STARTTASK_PRIO,
           STARTTASK_PRIO,
           (void *)&amp;StartTask_Stack[0],
           TASK_STACKSIZE,
           (void *) 0,  
           OS_TASK_OPT_STK_CHK | OS_TASK_OPT_STK_CLR);
  
    OSStart();
  
    return 0;
  }
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>Cruise Control 2014
  delay in ticks 100
  SWTimer was created but NOT started 
  SWTimer was started!
  All Tasks and Kernel Objects generated!
  Vehicle task created!
  SWTimer1 was created but NOT started 
  SWTimer1 was started!
  Control Task created!
  Position: 0m
  Velocity:  0.4m/s
  Throttle: 3V
  release key!
  released key!
  Control Task!
  Position: 0m
  Velocity:  0.9m/s
  Throttle: 4V
  release key!
  released key!
  Control Task!
  Position: 0m
  Velocity:  1.4m/s
  </code></pre>