使用硬件定时器定时的问题

发布于 2021-09-23 16:55:26 浏览：1160 订阅该版

大家好！我想请问一下我在使用stm32的硬件定时器，使用例程发现设定了5s的超时时间，但是实际计数大概是10s左右，这是什么原因呢？
```c
#include <rtthread.h>
#include <rtdevice.h>
#include <tim3.h>

#define HWTIMER_DEV_NAME   "timer3"     /* 定时器名称 */

/* 定时器超时回调函数 */
rt_err_t timeout_cb(rt_device_t dev, rt_size_t size)
{
    rt_kprintf("this is hwtimer timeout callback fucntion!\n");
    rt_kprintf("tick is :%d !\n", rt_tick_get());

return 0;
}

int hwtimer_sample(void)
{
    rt_err_t ret = RT_EOK;
    rt_hwtimerval_t timeout_s;      /* 定时器超时值 */
    rt_device_t hw_dev = RT_NULL;   /* 定时器设备句柄 */
    rt_hwtimer_mode_t mode;         /* 定时器模式 */

/* 查找定时器设备 */
    hw_dev = rt_device_find(HWTIMER_DEV_NAME);
    if (hw_dev == RT_NULL)
    {
        rt_kprintf("hwtimer sample run failed! can't find %s device!\n", HWTIMER_DEV_NAME);
        return RT_ERROR;
    }

/* 以读写方式打开设备 */
    ret = rt_device_open(hw_dev, RT_DEVICE_OFLAG_RDWR);
    if (ret != RT_EOK)
    {
        rt_kprintf("open %s device failed!\n", HWTIMER_DEV_NAME);
        return ret;
    }

/* 设置超时回调函数 */
    rt_device_set_rx_indicate(hw_dev, timeout_cb);

/* 设置模式为周期性定时器 */
    mode = HWTIMER_MODE_PERIOD;
    ret = rt_device_control(hw_dev, HWTIMER_CTRL_MODE_SET, &mode);
    if (ret != RT_EOK)
    {
        rt_kprintf("set mode failed! ret is :%d\n", ret);
        return ret;
    }

/* 设置定时器超时值为5s并启动定时器 */
    timeout_s.sec = 5;      /* 秒 */
    timeout_s.usec = 0;     /* 微秒 */

if (rt_device_write(hw_dev, 0, &timeout_s, sizeof(timeout_s)) != sizeof(timeout_s))
    {
        rt_kprintf("set timeout value failed\n");
        return RT_ERROR;
    }

/* 延时3500ms */
    rt_thread_mdelay(3500);

/* 读取定时器当前值 */
    rt_device_read(hw_dev, 0, &timeout_s, sizeof(timeout_s));
    rt_kprintf("Read: Sec = %d, Usec = %d\n", timeout_s.sec, timeout_s.usec);

return ret;
}

```
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![image.png](https://oss-club.rt-thread.org/uploads/20210923/88b1b0aa673ea83ec53b97c0578bdb49.png)