5 硬件定时器如何定us

发布于 2022-07-05 12:24:13 浏览：1118 订阅该版

在跑rtt硬件定时器例程的时候，发现几十微妙的定时是做不到的。最低只能1ms.于是用cube配置了下外部晶振的系统时钟，放在rtt的drv_clk.c。例程还是不能跑到微妙？
```c
static 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 */
    rt_uint32_t freq = 10000;               /* 计数频率 */

/* 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);

/* 设置计数频率(若未设置该项，默认为1Mhz 或 支持的最小计数频率) */
    rt_device_control(hw_dev, HWTIMER_CTRL_FREQ_SET, &freq);
    /* 设置模式为周期性定时器（若未设置，默认是HWTIMER_MODE_ONESHOT）*/
    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并启动定时器 */
    timeout_s.sec = 0;      /* 秒 */
     /* 微秒 */
    timeout_s.usec = 50;
    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;
    }

return ret;
}`

`void system_clock_config(int target_freq_Mhz)
{
    RCC_OscInitTypeDef RCC_OscInitStruct = {0};
      RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
      RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};

/** Initializes the RCC Oscillators according to the specified parameters
      * in the RCC_OscInitTypeDef structure.
      */
      RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
      RCC_OscInitStruct.HSEState = RCC_HSE_ON;
      RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;
      RCC_OscInitStruct.HSIState = RCC_HSI_ON;
      RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
      RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
      RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9;
      if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
      {
        Error_Handler();
      }

/** Initializes the CPU, AHB and APB buses clocks
      */
      RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                                  |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
      RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
      RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
      RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
      RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;

if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
      {
        Error_Handler();
      }
      PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_ADC;
      PeriphClkInit.AdcClockSelection = RCC_ADCPCLK2_DIV6;
      if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
      {
        Error_Handler();
      }
}
```