STM32嵌入式学习 03：TIM2 定时器更新中断

1. 本课目标

• 理解定时器相对阻塞式延时的优势。
• 理解 PSC、ARR、CNT 和更新事件。
• 根据公式计算定时器周期。
• 理解 TIM2 更新中断和 NVIC 的关系。
• 读懂 TIM2_IRQHandler()。

2. 知识主线

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path,#mermaid-svg-I3eTuLDvzAog1QWo .section-root circle,#mermaid-svg-I3eTuLDvzAog1QWo .section-root polygon{fill:hsl(240, 100%, 46.2745098039%);}#mermaid-svg-I3eTuLDvzAog1QWo .section-root text{fill:#ffffff;}#mermaid-svg-I3eTuLDvzAog1QWo .section-root span{color:#ffffff;}#mermaid-svg-I3eTuLDvzAog1QWo .section-2 span{color:#ffffff;}#mermaid-svg-I3eTuLDvzAog1QWo .icon-container{height:100%;display:flex;justify-content:center;align-items:center;}#mermaid-svg-I3eTuLDvzAog1QWo .edge{fill:none;}#mermaid-svg-I3eTuLDvzAog1QWo .mindmap-node-label{dy:1em;alignment-baseline:middle;text-anchor:middle;dominant-baseline:middle;text-align:center;}#mermaid-svg-I3eTuLDvzAog1QWo :root{--mermaid-font-family:"trebuchet ms",verdana,arial,sans-serif;} TIM2 定时器中断
时钟
RCC_APB1PeriphClockCmd
TIM2
APB1
定时器时钟
时基单元
PSC 预分频器
ARR 自动重装
CNT 计数器
向上计数
中断
更新事件
TIM_IT_Update
TIM2_IRQHandler
清除标志位
NVIC
中断通道
抢占优先级
响应优先级
通道使能
程序分工
主循环刷新 OLED
中断更新 Num
验证边界
依赖系统时钟
需要编译验证
需要硬件或仿真验证

3. 主程序

#include "stm32f10x.h"
#include "Delay.h"
#include "OLED.h"
#include "Timer.h"

uint16_t Num;

int main(void)
{
    OLED_Init();
    Timer_Init();

    OLED_ShowString(1, 1, "Num:");

    while (1)
    {
        // 主循环负责刷新显示，中断负责更新 Num
        OLED_ShowNum(1, 5, Num, 5);
    }
}

程序采用"中断更新数据、主循环显示数据"的分工：

TIM2 中断 -> Num++
主循环   -> OLED 显示 Num

4. TIM2 初始化

void Timer_Init(void)
{
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
    TIM_InternalClockConfig(TIM2);

    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
    TIM_TimeBaseInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInitStructure.TIM_Period = 10000 - 1;
    TIM_TimeBaseInitStructure.TIM_Prescaler = 7200 - 1;
    TIM_TimeBaseInitStructure.TIM_RepetitionCounter = 0;

    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitStructure);

    TIM_ClearFlag(TIM2, TIM_FLAG_Update);
    TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);

    NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);

    NVIC_InitTypeDef NVIC_InitStructure;
    NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 2;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
    NVIC_Init(&NVIC_InitStructure);

    TIM_Cmd(TIM2, ENABLE);
}

5. 定时器的工作过程

定时器输入时钟
    -> PSC 分频
    -> CNT 计数
    -> 达到 ARR
    -> 产生更新事件
    -> 触发 TIM2 更新中断

5.1 预分频器 PSC

TIM_TimeBaseInitStructure.TIM_Prescaler = 7200 - 1;

计数频率公式：

计数频率 = 定时器输入时钟 / (PSC + 1)

若 TIM2 输入时钟为 72 MHz：

72,000,000 / 7200 = 10,000 Hz

即每 0.1 ms 计数一次。

5.2 自动重装值 ARR

TIM_TimeBaseInitStructure.TIM_Period = 10000 - 1;

计数器向上计数：

0, 1, 2, ..., 9999

共计数 10000 次，因此：

10000 × 0.1 ms = 1000 ms = 1 s

6. 定时器周期公式

更新事件频率 = 定时器时钟 / ((PSC + 1) × (ARR + 1))

本工程在定时器时钟为 72 MHz 的假设下：

72,000,000 / (7200 × 10000) = 1 Hz

所以更新中断理论周期约为 1 秒，Num 理论上每秒加 1。

STM32F1 的 APB1 和定时器时钟存在倍频规则，不能只看 APB1 总线频率。必须结合工程的 RCC 和 SystemInit() 配置确认实际定时器输入时钟。

7. 为什么参数减 1

寄存器实际含义是：

分频系数 = PSC + 1
计数次数 = ARR + 1

因此希望分频 7200、计数 10000 次时，应写：

PSC = 7200 - 1;
ARR = 10000 - 1;

8. 更新中断与 NVIC

开启 TIM2 内部更新中断：

TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);

配置 CPU 的中断控制器：

NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

两层使能缺一不可：

TIM_ITConfig -> TIM2 外设允许产生中断
NVIC_Init    -> CPU 允许接收 TIM2 中断线路

抢占优先级决定一个中断能否打断另一个中断；响应优先级用于多个等待中断之间的先后判断。

9. 中断处理函数

void TIM2_IRQHandler(void)
{
    if (TIM_GetITStatus(TIM2, TIM_IT_Update) == SET)
    {
        Num++;
        TIM_ClearITPendingBit(TIM2, TIM_IT_Update);
    }
}

函数名必须与启动文件中的中断向量名称完全一致。TIM2_IRQHandler 不能改成自定义名称，否则 CPU 不会自动跳转到该函数。

进入中断后必须清除更新中断标志，否则中断请求可能持续有效，导致 CPU 反复进入中断函数，主程序表现为卡死或无法正常运行。

10. 程序流程图

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是
复位进入 main
OLED_Init
Timer_Init
打开 TIM2 时钟
配置 PSC 和 ARR
开启更新中断
配置 NVIC
启动 TIM2
主循环刷新 OLED
TIM2 自动计数
计数达到 ARR?
产生更新中断
TIM2_IRQHandler
Num++
清除更新中断标志

11. 易错点

• TIM_ITConfig() 和 NVIC_Init() 是两层不同的中断使能。
• 中断函数必须使用启动文件规定的准确名称。
• 进入中断后必须清除更新中断标志。
• PSC 和 ARR 的实际系数都要加 1。
• 不能只凭经验假设定时器时钟是 72 MHz。
• 中断函数应尽量短，不应放入复杂 OLED 刷新或长时间延时。
• Num 被主循环和中断共同访问，复杂场景应考虑 volatile 和原子访问问题。

12. 事实与验证边界

• 已知事实：源码使用 TIM2，配置 PSC = 7200 - 1、ARR = 10000 - 1，开启更新中断并在中断中执行 Num++。
• 合理推断：若 TIM2 输入时钟为 72 MHz 且初始化成功，更新中断理论周期约为 1 秒。
• 尚未确认：本次没有实际编译输出、OLED 显示结果或硬件/仿真中 Num 变化的证据。

13. 课后思考

1. 如果 ARR 改为 5000 - 1，在其他条件不变时中断周期是多少？
2. 如果希望中断周期为 10 ms，可以怎样选择 PSC 和 ARR？
3. 为什么 OLED 刷新放在主循环，而不是放进 TIM2 中断函数？
4. 忘记清除中断标志可能造成什么现象？

14. 下一步

后续可以学习定时器输出比较、PWM，或者把按键扫描改造成由定时器周期驱动的非阻塞状态机。