STM32 ordinary timer realizes delay function

/* SystemFrequency / 1000 1ms interrupt once

 * SystemFrequency / 100000 10us interruption

 * SystemFrequency / 1000000 1us interrupt once

 */

#define SYSTICKPERIOD                    0.000001

#define SYSTICKFREQUENCY            (1/SYSTICKPERIOD)

/**

  * @brief Initialization of timer 2, timing period 1ms

  * @param None

  * @retval None

  */

void TIM2_Init(void)

{

    TIM_TimeBaseInitTypeDef  TIM_TimeBaseStructure;

    /*AHB = 72MHz, PPRE1 of RCC_CFGR = 2, so APB1 = 36MHz, TIM2CLK = APB1*2 = 72MHz */

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    /* Time base configuration */         

    TIM_TimeBaseStructure.TIM_Period = 999;

    TIM_TimeBaseStructure.TIM_Prescaler = SystemCoreClock/SYSTICKFREQUENCY -1;

    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;

    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

    TIM_ARRPreloadConfig(TIM2, ENABLE);

    /* Set the update request source to generate an interrupt only when the counter overflows or underflows*/

    TIM_UpdateRequestConfig(TIM2,TIM_UpdateSource_Global); 

    TIM_ClearFlag(TIM2, TIM_FLAG_Update);

}

/**

  * @brief ms delay program, 1ms as a unit

  * @param  

  * @arg nTime: Delay_ms( 10 ) The delay achieved is 10 * 1ms = 10ms

  * @retval None

  */

void Delay_ms(__IO uint32_t nTime)

{     

    /* Clear the counter and enable the tick timer */  

    TIM2->CNT   = 0;  

    TIM_Cmd(TIM2, ENABLE);     

    for( ; nTime > 0 ; nTime--)

    {

     /* Wait for the end of a delay unit*/

     while(TIM_GetFlagStatus(TIM2, TIM_FLAG_Update) != SET);

     TIM_ClearFlag(TIM2, TIM_FLAG_Update);

    }

    TIM_Cmd(TIM2, DISABLE);

}