STM32 系统滴答计时器

static u8 fac_us = ;//us与系统滴答的被乘数
static unsigned short fac_ms = ;//ms与系统滴答的被乘数
static unsigned int m_sys_seconds = ;//系统运行秒数
/**
  * @description:系统滴答计时系统初始化
  * @param  无
  * @retval 无
  */
void SysTick_Init(void)
{
    //配置系统滴答时钟源
     SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK_Div8); //选择外部时钟  HCLK/8
     //设置预装载值
     SysTick->LOAD = 0x895440;//时间加载
     //计算ms & us转换因数
     fac_us = SystemCoreClock/; //为系统时钟的1/8
     fac_ms = (unsigned short)fac_us*;    //代表每个ms需要的systick时钟数    

     //开启中断,使能计时
     SysTick->CTRL |= (SysTick_CTRL_ENABLE_Msk | SysTick_CTRL_TICKINT_Msk) ; //开始倒数  

}

/*-------------------------------------------------------------------------------------------------
*@description: 返回当前系统运行的秒数.(溢出不计)
--------------------------------------------------------------------------------------------------*/
unsigned long sys_seconds(void)
{
 return m_sys_seconds;
}

/*-------------------------------------------------------------------------------------------------
*@description: 返回当前系统运行的时间,Unit ms.(溢出不计)
--------------------------------------------------------------------------------------------------*/
unsigned long long sys_millis(void)
{
 unsigned long long millisecond = (0x895440-SysTick->VAL)/fac_ms + m_sys_seconds*;
 //当前系统运行时间ms
 return millisecond;
}

/*-------------------------------------------------------------------------------------------------
*@description: 返回当前系统运行的时间,Unit us.(溢出不计)
--------------------------------------------------------------------------------------------------*/
unsigned long long sys_micros(void)
{
 unsigned long long microseconds = (0x895440-SysTick->VAL)/fac_us + m_sys_seconds*;
 return microseconds;
}

// couter 减1的时间 等于 1/systick_clk
// 当counter 从 reload 的值减小到0的时候，为一个循环，如果开启了中断则执行中断服务程序，
// 同时 CTRL 的 countflag 位会置1
// 这一个循环的时间为 reload * (1/systick_clk)

void SysTick_Delay_Us( unsigned short ns_num)
{
     unsigned long long current_us = sys_micros();

 if((current_us + ns_num) <= 0x3e7fffb7bbf)//不存在溢出
 {
  current_us += ns_num;
  do
  {
   ;
  }while(sys_micros() < current_us);
 }
 else//存在溢出
 {
  current_us = (current_us + ns_num) - 0x3e7fffb7bbf;
  do
  {
   ;
  }while(sys_micros() <= 0x3e7fffb7bbf);
  do
  {

  }while(sys_micros() < current_us);
 }
}

void SysTick_Delay_Ms( unsigned short ms_num)
{
    unsigned long long current_ms = sys_millis();

     if((current_ms + ms_num) <= 0xfffffed7)//不存在溢出
     {
      current_ms += ms_num;
      do
      {
       ;
      }while(sys_millis() < current_ms);
     }
     else//存在溢出
     {
      current_ms = (current_ms + ms_num) - 0xfffffed7;
      do
      {
       ;
      }while(sys_millis() <= 0xffffed7);
      do
      {
       ;
      }while(sys_millis() < current_ms);
     }

}

/**
  * @brief  This function handles SysTick Handler.
  * @param  None
  * @retval None
  */
void SysTick_Handler(void)
{
    m_sys_seconds++;
}