text: /**
   * @file systick.c
   * Provide access to the system tick with 1 millisecond resolution
   */
  
  /*********************
   *      INCLUDES
   *********************/
  #include "lv_hal_tick.h"
  #include <stddef.h>
  #include "../../lv_conf.h"
  
  /*********************
   *      DEFINES
   *********************/
  
  /**********************
   *      TYPEDEFS
   **********************/
  
  /**********************
   *  STATIC PROTOTYPES
   **********************/
  
  /**********************
   *  STATIC VARIABLES
   **********************/
  static uint32_t sys_time = 0;
  static volatile uint8_t tick_irq_flag;
  
  /**********************
   *      MACROS
   **********************/
  
  /**********************
   *   GLOBAL FUNCTIONS
   **********************/
  
  /**
   * You have to call this function periodically
   * @param tick_period the call period of this function in milliseconds
   */
  LV_ATTRIBUTE_TICK_INC void lv_tick_inc(uint32_t tick_period)
  {
      tick_irq_flag = 0;
      sys_time += tick_period;
  }
  
  /**
   * Get the elapsed milliseconds since start up
   * @return the elapsed milliseconds
   */
  uint32_t lv_tick_get(void)
  {
      uint32_t result;
      do {
          tick_irq_flag = 1;
          result = sys_time;
      } while(!tick_irq_flag);     /*'lv_tick_inc()' clears this flag which can be in an interrupt. Continue until make a non interrupted cycle */
  
      return result;
  }
  
  /**
   * Get the elapsed milliseconds science a previous time stamp
   * @param prev_tick a previous time stamp (return value of systick_get() )
   * @return the elapsed milliseconds since 'prev_tick'
   */
  uint32_t lv_tick_elaps(uint32_t prev_tick)
  {
  	uint32_t act_time = lv_tick_get();
  
  	/*If there is no overflow in sys_time simple subtract*/
  	if(act_time >= prev_tick) {
  		prev_tick = act_time - prev_tick;
  	} else {
  		prev_tick = UINT32_MAX - prev_tick + 1;
  		prev_tick += act_time;
  	}
  
  	return prev_tick;
  }
  
  /**********************
   *   STATIC FUNCTIONS
   **********************/
  
  