STM32 study notes (7)

Systick tick timer of STM32F103ZET6

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Preface

The learning of STM32 can be divided into 3 versions.
1. Register version
2. Library function version
3. HAL library version
Due to personal reasons, I choose the library function version to learn STM32.

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Tip: Problems such as software installation will not be explained! ! !

1. Introduction to Systick Timer

2. Related registers

1. Control and Status Register (CTRL) (Address 0xE000_E010)

2. Reload the value register (LOAD) (0xE000_E014)

3. Current value register (VAL) (Address: 0xE000_E018)

4. Calibration value register (CALIB) (Address: 0xE000_E01C)

Three, generate interrupts to achieve delay

1.delay_init function

code show as below:

void delay_init()
{
    
    
	#if SYSTEM_SUPPORT_OS //如果需要支持 OS.
	u32 reload;
	#endif
	SysTick_CLKSourceConfig(SysTick_CLKSource_HCLK_Div8);
	//选择外部时钟 HCLK/8
	fac_us=SystemCoreClock/8000000; //为系统时钟的 1/8
	#if SYSTEM_SUPPORT_OS //如果需要支持 OS.
	reload=SystemCoreClock/8000000; //每秒钟的计数次数 单位为 K
	reload*=1000000/delay_ostickspersec; //根据 delay_ostickspersec 设定溢出时间
	//reload 为 24 位寄存器,最大值:16777216,在 72M 下,约合 1.86s 左右
	fac_ms=1000/delay_ostickspersec; //代表 OS 可以延时的最少单位
	SysTick->CTRL|=SysTick_CTRL_TICKINT_Msk; //开启 SYSTICK 中断
	SysTick->LOAD=reload; //每 1/os_delay_tickspersec 秒中断一次
	SysTick->CTRL|=SysTick_CTRL_ENABLE_Msk; //开启 SYSTICK
	#else
	fac_ms=(u16)fac_us*1000; //非 OS 下,代表每个 ms 需要的 systick 时钟数
	#endif
}

2.delay_us function

code show as below:

//延时nus
//nus为要延时的us数.		    								   
void delay_us(u32 nus)
{
    
    		
	u32 temp;	    	 
	SysTick->LOAD=nus*fac_us; 					//时间加载	  		 
	SysTick->VAL=0x00;        					//清空计数器
	SysTick->CTRL|=SysTick_CTRL_ENABLE_Msk ;	//开始倒数	  
	do
	{
    
    
		temp=SysTick->CTRL;
	}while((temp&0x01)&&!(temp&(1<<16)));		//等待时间到达   
	SysTick->CTRL&=~SysTick_CTRL_ENABLE_Msk;	//关闭计数器
	SysTick->VAL =0X00;      					 //清空计数器	 
}

3.delay_ms function

code show as below:

//延时nms
//注意nms的范围
//SysTick->LOAD为24位寄存器,所以,最大延时为:
//nms<=0xffffff*8*1000/SYSCLK
//SYSCLK单位为Hz,nms单位为ms
//对72M条件下,nms<=1864 
void delay_ms(u16 nms)
{
    
    	 		  	  
	u32 temp;		   
	SysTick->LOAD=(u32)nms*fac_ms;				//时间加载(SysTick->LOAD为24bit)
	SysTick->VAL =0x00;							//清空计数器
	SysTick->CTRL|=SysTick_CTRL_ENABLE_Msk ;	//开始倒数  
	do
	{
    
    
		temp=SysTick->CTRL;
	}while((temp&0x01)&&!(temp&(1<<16)));		//等待时间到达   
	SysTick->CTRL&=~SysTick_CTRL_ENABLE_Msk;	//关闭计数器
	SysTick->VAL =0X00;       					//清空计数器	  	    
} 

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to sum up

Source code analysis: while((temp&0x01)&&!(temp&(1<<16))); //Waiting time reaches
temp&0x01: Take the 1st bit of the CTRL register, if it is 1, the timer is enabled
temp&(1<<16) : Take the 16th bit of the CTRL register, if it is 1, the countdown is 0