火龙果MM32F3273G8P开发板MindSDK开发教程4 - 滴嗒定时器Systick的配置

1、Systick寄存器

Systick是ARM内核的一个外设，所以在不同芯片的代码上移植比较方便，他总共有4个寄存器，
从Systick定义中可以看到：

typedef struct
{
  __IOM uint32_t CTRL;                   /*!< Offset: 0x000 (R/W)  SysTick Control and Status Register */
  __IOM uint32_t LOAD;                   /*!< Offset: 0x004 (R/W)  SysTick Reload Value Register */
  __IOM uint32_t VAL;                    /*!< Offset: 0x008 (R/W)  SysTick Current Value Register */
  __IM  uint32_t CALIB;                  /*!< Offset: 0x00C (R/ )  SysTick Calibration Register */
} SysTick_Type;

2、轮询方式延时

一般，systick ms级别的延时，采用中断方式，load值为sysclk/1000，这样每ms产生中断，可以用来ms级别的延时，或者为freeRtos提供节拍。
同样，采用轮询方式延时，也可以实现ms级的延时，并且可以实现us级的延时。
systick的时钟源分两种，ctrl寄存器第二位为0时采用sysclk/8的时钟频率，第二位为1时采用系统时钟。
轮询方式延时采用sysclk/8分频方式，也可以采用不分频的方式。

a、采用8分频的方式

假如系统时钟为120M，8分频后为15M，即1/15000000计一次数，1us需要15次。所以代码中倍频因子为了代码的可移植性，使其count_1us = sysclk/8000000 = 15。
相关代码：

volatile static float count_1us = 0;
volatile static float count_1ms = 0;

/**
 *  初始化滴答定时器函数
 *  轮询方式延时
*/

void BOARD_Systick_Init()
{
	// Systick CTRL 寄存器 第二位为0时，Systick时钟==Sysclk/8 ,
	// 第二位为1时，Systick = Sysclk
	SysTick->CTRL &= ~(1<<2);// 将systick使用内核时钟，根据时钟树，即120/8=15M;
	
	count_1us = (float)(CLOCK_GetBootHSEValue()/8000000);
	count_1ms = (float)1000*count_1us;
}

void BOARD_Delay1Us(uint32_t count)
{
	uint32_t ctl;

	/* reload the count value */
    SysTick->LOAD = (uint32_t)(count * count_1us);
    /* clear the current count value */
    SysTick->VAL = 0x0000U;
    /* enable the systick timer */
    SysTick->CTRL = SysTick_CTRL_ENABLE_Msk;
    /* wait for the COUNTFLAG flag set */
    do{
        ctl = SysTick->CTRL;
    }while((ctl&SysTick_CTRL_ENABLE_Msk)&&!(ctl & SysTick_CTRL_COUNTFLAG_Msk));
    /* disable the systick timer */
    SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
    /* clear the current count value */
    SysTick->VAL = 0x0000U;
	
}

void BOARD_Delay1Ms(uint32_t count)
{
    uint32_t ctl;
    
    /* reload the count value */
    SysTick->LOAD = (uint32_t)(count * count_1ms);
    /* clear the current count value */
    SysTick->VAL = 0x0000U;
    /* enable the systick timer */
    SysTick->CTRL = SysTick_CTRL_ENABLE_Msk;
    /* wait for the COUNTFLAG flag set */
    do{
        ctl = SysTick->CTRL;
    }while((ctl&SysTick_CTRL_ENABLE_Msk)&&!(ctl & SysTick_CTRL_COUNTFLAG_Msk));
    /* disable the systick timer */
    SysTick->CTRL &= ~SysTick_CTRL_ENABLE_Msk;
    /* clear the current count value */
    SysTick->VAL = 0x0000U;
}

实验现象
BOARD_Delay1Ms(1000)
BOARD_Delay1Us(1000)
产生的对应波形为
在这里插入图片描述

在这里插入图片描述

b、采用不分频的方式

设置systick的时钟=sysclk=120M，所以1us需要计数120次,1ms需要计数120*1000次。
us延时设置LOAD寄存器=sysclk/1000000；
ms延时设置LOAD寄存器=sysclk/1000；
当每次计数结束时，就是LOAD减为0的时候，CTRL寄存器的16位会置为1，我们监测这位的数值即可实现延时。这里同上面一样
实现代码

uint32_t BOARD_Systick_Init(uint32_t ticks)
{ 
  if (ticks > SysTick_LOAD_RELOAD_Msk)  return (1);            /* Reload value impossible */
                                                               
  SysTick->LOAD  = (ticks & SysTick_LOAD_RELOAD_Msk) - 1;      /* set reload register */
  NVIC_SetPriority (SysTick_IRQn, (1<<__NVIC_PRIO_BITS) - 1);  /* set Priority for Cortex-M0 System Interrupts */
  SysTick->VAL   = 0;                                          /* Load the SysTick Counter Value */
  SysTick->CTRL  = SysTick_CTRL_CLKSOURCE_Msk | 
                   SysTick_CTRL_ENABLE_Msk;                    /* Enable SysTick IRQ and SysTick Timer */
  SysTick->CTRL  &= ~SysTick_CTRL_TICKINT_Msk;
  return (0);                                                  /* Function successful */
}

void BOARD_Delay1Us( __IO uint32_t us)
{
	uint32_t i;	
	BOARD_Systick_Init(CLOCK_GetBootHSEValue() / 1000000);
	
	for(i=0;i<us;i++)
	{
		/* When the counter value decreases to 0, bit 16 of the CRTL register will be set to 1 */
		/* When set to 1, reading this bit will clear it to 0 */
		while( !((SysTick->CTRL)&(1<<16)) );
	}
	/* Turn off the SysTick timer */
	SysTick->CTRL &=~ SysTick_CTRL_ENABLE_Msk;
}

void BOARD_Delay1Ms( __IO uint32_t ms)
{
	uint32_t i;	
	BOARD_Systick_Init(CLOCK_GetBootHSEValue() / 1000);
	
	for(i=0;i<ms;i++)
	{
		/* When the counter value decreases to 0, bit 16 of the CRTL register will be set to 1 */
		/* When set to 1, reading this bit will clear it to 0 */
		while( !((SysTick->CTRL)&(1<<16)) );
	}
	/* Turn off the SysTick timer */
	SysTick->CTRL &=~ SysTick_CTRL_ENABLE_Msk;
}

中断方式延时

设置每1ms触发中断，在中断里记录中断次数，亦可实现ms级的延时。

volatile static uint32_t delay;

uint32_t BOARD_Systick_Init(uint32_t ticks)
{ 
  if (ticks > SysTick_LOAD_RELOAD_Msk)  return (1);            /* Reload value impossible */
                                                               
  SysTick->LOAD  = (ticks & SysTick_LOAD_RELOAD_Msk) - 1;      /* set reload register */
  NVIC_SetPriority (SysTick_IRQn, (1<<__NVIC_PRIO_BITS) - 1);  /* set Priority for Cortex-M0 System Interrupts */
  SysTick->VAL   = 0;                                          /* Load the SysTick Counter Value */
  SysTick->CTRL  = SysTick_CTRL_CLKSOURCE_Msk | 
                   SysTick_CTRL_ENABLE_Msk;                    /* Enable SysTick IRQ and SysTick Timer */
  SysTick->CTRL  |= SysTick_CTRL_TICKINT_Msk;
  return (0);                                                  /* Function successful */
}

void BOARD_Delay1Ms(uint32_t count)
{
    delay = count;

    while(0U != delay){
    }
}

void BOARD_Delay_Decrement(void)
{
    if (0U != delay){
        delay--;
    }
}

void SysTick_Handler(void)
{
	BOARD_Delay_Decrement();
}