一、简介

SysTick —系统定时器是属于 CM3 内核中的一个外设，内嵌在 NVIC 中。系统定时器是一个 24bit 的向下递减的计数器，计数器每计数一次的时间为 1/SYSCLK，一般我们设置系统时钟 SYSCLK 等于 108M。当重装载数值寄存器的值递减到 0 的时候，系统定时器就产生一次中断，以此循环往复。

因为 SysTick 是属于 CM3 内核的外设，所以所有基于 CM3 内核的单片机都具有这个系统定时器，使得软件在 CM3 单片机中可以很容易的移植。系统定时器一般用于操作系统，用于产生时基，维持操作系统的心跳。

二、API说明

2.1 外设寄存器说明

SysTick寄存器列表如下表所示：

参考 core_cm3.h 文件中定义的结构体类型 SysTick_Type

2.2 外设库函数说明

以下 SYSTICK 接口位于 GD32F10x_Firmware_Library_V2.2.2\Firmware\GD32F10x_standard_peripheral\Include\gd32f10x_misc.h。

2.2.1 systick_clksource_set

systick_clksource： SysTick时钟源，详细列表如下：

三、中断方式

3.1 systick.c

/*!
    \file    systick.c
    \brief   the systick configuration file

    \version 2014-12-26, V1.0.0, firmware for GD32F10x
    \version 2017-06-20, V2.0.0, firmware for GD32F10x
    \version 2018-07-31, V2.1.0, firmware for GD32F10x
    \version 2020-09-30, V2.2.0, firmware for GD32F10x
*/

/*
    Copyright (c) 2020, GigaDevice Semiconductor Inc.

    Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, this 
       list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice, 
       this list of conditions and the following disclaimer in the documentation 
       and/or other materials provided with the distribution.
    3. Neither the name of the copyright holder nor the names of its contributors 
       may be used to endorse or promote products derived from this software without 
       specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
OF SUCH DAMAGE.
*/

#include "gd32f10x.h"
#include "systick.h"

volatile static uint32_t delay;

/*!
    \brief      configure systick
    \param[in]  none
    \param[out] none
    \retval     none
*/
void systick_config(void)
{
    /* setup systick timer for 1000Hz interrupts */
    if (SysTick_Config(SystemCoreClock / 1000U)){
        /* capture error */
        while (1){
        }
    }
    /* configure the systick handler priority */
    NVIC_SetPriority(SysTick_IRQn, 0x00U);
}

/*!
    \brief      delay a time in milliseconds
    \param[in]  count: count in milliseconds
    \param[out] none
    \retval     none
*/
void delay_1ms(uint32_t count)
{
    delay = count;

    while(0U != delay){
    }
}

/*!
    \brief      delay decrement
    \param[in]  none
    \param[out] none
    \retval     none
*/
void delay_decrement(void)
{
    if (0U != delay){
        delay--;
    }
}

SysTick 初始化函数由用户编写，里面调用了 SysTick_Config() 这个固件库函数，通过设置该固件库函数的形参，就决定了系统定时器经过多少时间就产生一次中断。

• SysTick 中断时间的计算
  SysTick 定时器的计数器是向下递减计数的，计数一次的时间 ，当重装载寄存器中的值 减到0的时候，产生中断，可知中断一次的时间
  ，其中 。 如果设置 为 108，那中断一次的时间 。不过 1us 的中断没啥意义，整个程序的重心都花在进出中断上了，根本没有时间处理其他的任务。

SysTick_Config(SystemCoreClock / 1000))

SysTick_Config() 的形我们配置为 ，从刚刚分析我们知道这个形参的值最终是写到重装载寄存器 LOAD 中的，从而可知我们现在把 SysTick 定时器中断一次的时间 。

• SysTick 定时时间的计算
  当设置好中断时间 后，我们可以设置一个变量 t，用来记录进入中断的次数，那么变量 t 乘以中断的时间 就可以计算出需要定时的时间。

• SysTick 定时函数
  现在我们定义一个毫秒级别的延时函数，形参为 count，当用这个形参乘以中断时间 就得出我们需要的延时时间。

/*!
    \brief      delay a time in milliseconds
    \param[in]  count: count in milliseconds
    \param[out] none
    \retval     none
*/
void delay_1ms(uint32_t count)
{
    delay = count;

    while(0U != delay){
    }
}

函数 delay_1ms() 中我们等待 delay 为 0，当 delay 为 0 的时候表示延时时间到。变量 delay 在中断函数中递减，即 SysTick 每进一次中断即 1ms 的时间 delay 递减一次。

3.2 systick.h

/*!
    \file    systick.h
    \brief   the header file of systick

    \version 2014-12-26, V1.0.0, firmware for GD32F10x
    \version 2017-06-20, V2.0.0, firmware for GD32F10x
    \version 2018-07-31, V2.1.0, firmware for GD32F10x
    \version 2020-09-30, V2.2.0, firmware for GD32F10x
*/

/*
    Copyright (c) 2020, GigaDevice Semiconductor Inc.

    Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, this 
       list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice, 
       this list of conditions and the following disclaimer in the documentation 
       and/or other materials provided with the distribution.
    3. Neither the name of the copyright holder nor the names of its contributors 
       may be used to endorse or promote products derived from this software without 
       specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
OF SUCH DAMAGE.
*/

#ifndef SYSTICK_H
#define SYSTICK_H

#include <stdint.h>

/* configure systick */
void systick_config(void);
/* delay a time in milliseconds */
void delay_1ms(uint32_t count);
/* delay decrement */
void delay_decrement(void);

#endif /* SYSTICK_H */

3.3 gd32f10x_it.c

/*!
    \file    gd32f10x_it.c
    \brief   interrupt service routines

    \version 2014-12-26, V1.0.0, firmware for GD32F10x
    \version 2017-06-20, V2.0.0, firmware for GD32F10x
    \version 2018-07-31, V2.1.0, firmware for GD32F10x
    \version 2020-09-30, V2.2.0, firmware for GD32F10x
*/

/*
    Copyright (c) 2020, GigaDevice Semiconductor Inc.

    Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, this 
       list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice, 
       this list of conditions and the following disclaimer in the documentation 
       and/or other materials provided with the distribution.
    3. Neither the name of the copyright holder nor the names of its contributors 
       may be used to endorse or promote products derived from this software without 
       specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
OF SUCH DAMAGE.
*/
#include "gd32f10x_it.h"
#include "systick.h"

/*!
    \brief      this function handles NMI exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void NMI_Handler(void)
{
}

/*!
    \brief      this function handles HardFault exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void HardFault_Handler(void)
{
    /* if Hard Fault exception occurs, go to infinite loop */
    while(1){
    }
}

/*!
    \brief      this function handles MemManage exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void MemManage_Handler(void)
{
    /* if Memory Manage exception occurs, go to infinite loop */
    while(1){
    }
}

/*!
    \brief      this function handles BusFault exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void BusFault_Handler(void)
{
    /* if Bus Fault exception occurs, go to infinite loop */
    while(1){
    }
}

/*!
    \brief      this function handles UsageFault exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void UsageFault_Handler(void)
{
    /* if Usage Fault exception occurs, go to infinite loop */
    while(1){
    }
}

/*!
    \brief      this function handles SVC exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void SVC_Handler(void)
{
}

/*!
    \brief      this function handles DebugMon exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void DebugMon_Handler(void)
{
}

/*!
    \brief      this function handles PendSV exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void PendSV_Handler(void)
{
}

/*!
    \brief      this function handles SysTick exception
    \param[in]  none
    \param[out] none
    \retval     none
*/
void SysTick_Handler(void)
{
    delay_decrement();
}

• SysTick 中断服务函数

void SysTick_Handler(void)
{
    delay_decrement();
}

中断复位函数调用了另外一个函数 delay_decrement()，原型如下：

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

delay 的值等于延时函数中传进去的 count 的值，比如 count=1000，则延时的时间等于 1000*1ms=1s。

3.4 main.c

#include "gd32f10x.h"
#include "systick.h"

int main(void)
{
    systick_config();//系统主频108MHZ,采用外部晶振,由两个宏决定(__SYSTEM_CLOCK_108M_PLL_HXTAL与HXTAL_VALUE)
    
    LED_GPIO_Init();// LED灯模块初始化
    
    while(1)
    {
          LED_ON;
          delay_1ms(500);
          LED_OFF;
          delay_1ms(500);
    }
}

四、轮询方式

直接方便，套路浅

4.1 systick.c

/*!
    \file    systick.c
    \brief   the systick configuration in polling mode

    \version 2020-09-30, V1.0.0, firmware for GD32F10x
*/

/*
    Copyright (c) 2020, GigaDevice Semiconductor Inc.

    Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, this 
       list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice, 
       this list of conditions and the following disclaimer in the documentation 
       and/or other materials provided with the distribution.
    3. Neither the name of the copyright holder nor the names of its contributors 
       may be used to endorse or promote products derived from this software without 
       specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
OF SUCH DAMAGE.
*/

#include "gd32f10x.h"
#include "systick.h"

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

/*!
    \brief      configure systick
    \param[in]  none
    \param[out] none
    \retval     none
*/
void systick_config(void)
{
    /* systick clock source is from HCLK/8 内部时钟的108M/8分频 */
    systick_clksource_set(SYSTICK_CLKSOURCE_HCLK_DIV8);
    count_1us = (float)SystemCoreClock/8000000;//延时1us需要的时钟数量 108M/8M = 13.5 
    count_1ms = (float)count_1us * 1000;//延时1ms需要的时钟数量 108M/8M *1000= 13500 
}

/*!
    \brief      delay a time in microseconds in polling mode
    \param[in]  count: count in microseconds
    \param[out] none
    \retval     none
*/
void delay_1us(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;
}

/*!
    \brief      delay a time in milliseconds in polling mode
    \param[in]  count: count in milliseconds
    \param[out] none
    \retval     none
*/
void delay_1ms(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;
}

GD32F103通过AHB时钟(HCLK)即108MHz的8分频后作为Cortex系统定时器(SysTick)的外部时钟。

4.2 systick.h

/*!
    \file    systick.h
    \brief   the header file of systick

    \version 2020-09-30, V1.0.0, firmware for GD32F10x
*/

/*
    Copyright (c) 2020, GigaDevice Semiconductor Inc.

    Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:

    1. Redistributions of source code must retain the above copyright notice, this 
       list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright notice, 
       this list of conditions and the following disclaimer in the documentation 
       and/or other materials provided with the distribution.
    3. Neither the name of the copyright holder nor the names of its contributors 
       may be used to endorse or promote products derived from this software without 
       specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
OF SUCH DAMAGE.
*/

#ifndef SYSTICK_H
#define SYSTICK_H

#include <stdint.h>

/* configure systick */
void systick_config(void);
/* delay a time in milliseconds */
void delay_1ms(uint32_t count);
/* delay a time in microseconds */
void delay_1us(uint32_t count);

#endif /* SYSTICK_H */

4.3 main.c

#include "gd32f10x.h"
#include "systick.h"

int main(void)
{
    systick_config();//系统主频108MHZ,采用外部晶振,由两个宏决定(__SYSTEM_CLOCK_108M_PLL_HXTAL与HXTAL_VALUE)
    
    LED_GPIO_Init();// LED灯模块初始化
    
    while(1)
    {
          LED_ON;
          delay_1ms(500);
          LED_OFF;
          delay_1us(500000);
    }
}

• 由 Leung 写于 2022 年 4 月 13 日

• 参考：14. GD32F103C8T6入门教程-Systick定时器
　　　　GD32精确延时和时间戳