10 硬件定时器如何配置固定频率

发布于 2021-09-27 10:10:53 浏览：1365 订阅该版

红枫认证专家 2021-09-27

这家伙很懒，什么也没写！

leefeng 2021-09-28

这家伙很懒，什么也没写！

感谢指点！

分享下我现在的解决方法：
主要还是参考“HWTIMER 设备”
https://www.rt-thread.org/document/site/#/rt-thread-version/rt-thread-standard/programming-manual/device/hwtimer/hwtimer

这里面的“计数频率”就是我们要设置的频率；

之所以之前没有成功，是因为和下面rt_device_write()里面设置的时间冲突了，所以对里面做了些小改动。

rt_device_write()本质是调用的“rt-thread\components\drivers\hwtimer\hwtimer.c” 里面的rt_hwtimer_write()函数。

```
static rt_size_t rt_hwtimer_write(struct rt_device *dev, rt_off_t pos, const void *buffer, rt_size_t size)
{
    rt_uint32_t t = 1000;
    rt_hwtimer_mode_t opm = HWTIMER_MODE_PERIOD;
    rt_hwtimer_t *timer;

timer = (rt_hwtimer_t *)dev;
    if ((timer->ops->start == RT_NULL) || (timer->ops->stop == RT_NULL))
        return 0;

if(pos == 0)
    {
        if (size != sizeof(rt_hwtimerval_t))
            return 0;

t = timeout_calc(timer, (rt_hwtimerval_t*)buffer);
    }

if(pos == 1)
    {
        if (size != sizeof(rt_uint32_t))
            return 0;
        
        t = *(rt_uint32_t *)buffer;
    }

timer->ops->stop(timer);
    timer->overflow = 0;

if ((timer->cycles <= 1) && (timer->mode == HWTIMER_MODE_ONESHOT))
    {
        opm = HWTIMER_MODE_ONESHOT;
    }

if (timer->ops->start(timer, t, opm) != RT_EOK)
        size = 0;

return size;
}
```

调用的时候就是把之前传时间的改为传“溢出值”，pos设置为1(代表溢出值模式)；
```
    rt_device_t hw_dev = RT_NULL;   /* 定时器设备句柄 */
    rt_hwtimer_mode_t mode;         /* 定时器模式 */
    rt_uint32_t freq = 128000;       /* 计数频率 */
    rt_uint32_t overflow = 5;       /* 溢出值 */

/* 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);
    }

/* 以读写方式打开硬件定时器 */
    ret = rt_device_open(hw_dev, RT_DEVICE_OFLAG_RDWR);
    if (ret != RT_EOK)
    {
        rt_kprintf("open %s device failed!\n", HWTIMER_DEV_NAME);
    }
    
    /* 设置超时回调函数 */
    rt_device_set_rx_indicate(hw_dev, timeout_cb);
    
    /* 设置计数频率(默认1Mhz或支持的最小计数频率) */
    ret = rt_device_control(hw_dev, HWTIMER_CTRL_FREQ_SET, &freq);
    if (ret != RT_EOK)
    {
        rt_kprintf("set frequency failed! ret is :%d\n", ret);
    }
    
    /* 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);
    }

/* 设置定时器溢出值并启动定时器 */
    if (rt_device_write(hw_dev, 1, &overflow, sizeof(overflow)) != sizeof(overflow))
    {
        rt_kprintf("set timeout value failed\n");
    }
```

有更好的解决方法，请指正。谢谢！