STM32改写Finsh为RS485接口,不能接收

STM32F103
正在改写Finsh为RS485接口方式，在usart.c文件中
```static int stm32_putc(struct rt_serial_device serial, char c)
{
struct stm32_uart uart;

RT_ASSERT(serial != RT_NULL);
RS485Send_Enable();//切换RS485到发送状态
uart = (struct stm32_uart *)serial->parent.user_data;
while (!(uart->uart_device->SR & USART_FLAG_TXE));
uart->uart_device->DR = c;

// dealy_ms(10);
// RS485Receive_Enable();//切换RS485到接收状态

return 1;

}```

可以正常发送，但接收键盘输入出错.

又仔细看了下,貌似应该修改shell.c中的void finsh_thread_entry(void* parameter)函数

``` while (1)
{
/ wait receive /
if (rt_sem_take(&shell->rx_sem, RT_WAITING_FOREVER) != RT_EOK) continue;

      // RS485Receive_Enable();//切换RS485到接收状态
    /* read one character from device */
    while (rt_device_read(shell->device, 0, &ch, 1) == 1)
    {
      .......

```

此处,
rt_sem_take(&shell->rx_sem, RT_WAITING_FOREVER) != RT_EOK) continue;
串口有接收到数据时触发信号量,才进行while (rt_device_read(shell->device, 0, &ch, 1) == 1)

切换RS485到接收状态操作应该加到什么位置呢?