新塘M051 关于 System Tick设置，3种方法操作

关于 System Tick设置，给出3种方法，学习并确认OK：

使用 M051BSPv3.01.001版本

一、使用函数CLK_EnableSysTick（）

1 //Enable System Tick counter, Select HXT/2 as the clock source of SysTick,reload value. It could be 0~0xFFFFFF.
2 //HXT=12mHZ=（1/12）us
3 //12000*（1/12）=1000us=1ms 即1ms中断一次
4 CLK_EnableSysTick(CLK_CLKSEL0_STCLK_S_HXT, 12000);

函数CLK_EnableSysTick（）在CLK.C

注意：此函数有保护寄存器操作，所在需在解保时执行。

 1 /**
 2   * @brief      Enable System Tick counter
 3   * @param[in]  u32ClkSrc is System Tick clock source. Including:
 4   *             - \ref CLK_CLKSEL0_STCLK_S_HXT
 5   *             - \ref CLK_CLKSEL0_STCLK_S_HXT_DIV2
 6   *             - \ref CLK_CLKSEL0_STCLK_S_HCLK_DIV2
 7   *             - \ref CLK_CLKSEL0_STCLK_S_HIRC_DIV2
 8   *             - \ref CLK_CLKSEL0_STCLK_S_HCLK
 9   * @param[in]  u32Count is System Tick reload value. It could be 0~0xFFFFFF.
10   * @return     None
11   * @details    This function set System Tick clock source, reload value, enable System Tick counter and interrupt.
12   *             The register write-protection function should be disabled before using this function.
13   */
14 void CLK_EnableSysTick(uint32_t u32ClkSrc, uint32_t u32Count)
15 {
16     /* Set System Tick counter disabled */
17     SysTick->CTRL = 0;
18
19     /* Set System Tick clock source */
20     if( u32ClkSrc == CLK_CLKSEL0_STCLK_S_HCLK )
21         SysTick->CTRL |= SysTick_CTRL_CLKSOURCE_Msk;
22     else
23         CLK->CLKSEL0 = (CLK->CLKSEL0 & ~CLK_CLKSEL0_STCLK_S_Msk) | u32ClkSrc;
24
25     /* Set System Tick reload value */
26     SysTick->LOAD = u32Count;
27
28     /* Clear System Tick current value and counter flag */
29     SysTick->VAL = 0;
30
31     /* Set System Tick interrupt enabled and counter enabled */
32     SysTick->CTRL |= SysTick_CTRL_TICKINT_Msk | SysTick_CTRL_ENABLE_Msk;
33 }

二、使用函数SysTick_Config（）

1         if (SysTick_Config(SysTick_int_us*50))//此函数SysTick时钟源默认为系统时钟源。
2         {
3                 //Capture error
4                 do
5                     printf("SysTick_Init_失败 \n\n\n");
6                 while (1);
7         }
8         else
9                 printf("SysTick_Init_成功 \n");

此函数在core_cm0.h

 1 /** \brief  System Tick Configuration
 2
 3     The function initializes the System Timer and its interrupt, and starts the System Tick Timer.
 4     Counter is in free running mode to generate periodic interrupts.
 5
 6     \param [in]  ticks  Number of ticks between two interrupts.
 7
 8     \return          0  Function succeeded.
 9     \return          1  Function failed.
10
11     \note     When the variable <b>__Vendor_SysTickConfig</b> is set to 1, then the
12     function <b>SysTick_Config</b> is not included. In this case, the file <b><i>device</i>.h</b>
13     must contain a vendor-specific implementation of this function.
14
15  */
16 __STATIC_INLINE uint32_t SysTick_Config(uint32_t ticks)
17 {
18   if (ticks > SysTick_LOAD_RELOAD_Msk)  return (1);            /* Reload value impossible */
19
20   SysTick->LOAD  = (ticks & SysTick_LOAD_RELOAD_Msk) - 1;      /* set reload register */
21   NVIC_SetPriority (SysTick_IRQn, (1<<__NVIC_PRIO_BITS) - 1);  /* set Priority for Systick Interrupt */
22   SysTick->VAL   = 0;                                          /* Load the SysTick Counter Value */
23   SysTick->CTRL  = SysTick_CTRL_CLKSOURCE_Msk |
24                    SysTick_CTRL_TICKINT_Msk   |
25                    SysTick_CTRL_ENABLE_Msk;                    /* Enable SysTick IRQ and SysTick Timer */
26   return (0);                                                  /* Function successful */
27 }

三、直接寄存器操作

 1         //主时钟为：50Mhz
 2         //HXT=50mHZ=1/50us 50000*1/50=1000us=1ms//OK
 3         //重装载值=ticks 时钟频率(Hz)X想要的定时时间（S）=50x1000=50000
 4         //SysTick控制与状态（SYST_CSR）
 5         SysTick->CTRL  =    SysTick_CTRL_CLKSOURCE_Msk |    // 1= 内核时钟用于SysTick.
 6                             SysTick_CTRL_TICKINT_Msk   |    // 1:向下计数到0将引起SysTick中断。清SysTick当前值寄存器SYST_CVR的值将清除SysTick中断.
 7                             SysTick_CTRL_ENABLE_Msk;        // ENABLE:1:计数器运行于多脉冲方式. 0:禁用计数器
 8                                                             // COUNTFLAG:计数由1到0时，COUNTFLAG 置位.在读该位或向系统定时器当前值寄存器（SYST_CVR）写时，COUNTFLAG 被清零。
 9         //SysTick重装载值寄存器（SYST_RVR）
10         SysTick->LOAD  = ((SysTick_int_us*50) & SysTick_LOAD_RELOAD_Msk) - 1; //RELOAD:当计数器达到0时，值加载到当前值寄存器.
11
12         //SysTick当前值寄存器（SYST_CVR）
13         SysTick->VAL   = 0;            //CURRENT:该寄存器为写清零软件写入任何值将清寄存器为0。
14
15         // set Priority for Systick Interrupt
16         //NVIC_SetPriority (SysTick_IRQn, (1<<__NVIC_PRIO_BITS) - 1);
17         NVIC_EnableIRQ(SysTick_IRQn);

最后中断入口程序：

 1 /*******************************************************************
 2 功能        ：SysTick中断入口
 3 说明        ：嘀嗒心跳
 4 入口参数     ：无
 5 返回值      ：无
 6 应用子程序   ：
 7 全局变量     ：
 8 *******************************************************************/
 9 void SysTick_Handler(void)                //非SysTick_IRQHandler(void)
10 {
11     SysTick_CountValue_Add();            //计数加1
12     /*SysTick当前值寄存器（SYST_CVR）*/
13     SysTick->VAL   = 0;                  //CURRENT:该寄存器为写清零,软件写入任何值将清寄存器为0，写值清中断
14     GPIO_TOGGLE(P00);                    //Test 1ms P00切换一次电平
15 }