_serial_fifo_tx_blocking_buf实现疑惑

发布于 2022-05-27 11:42:37 浏览：468 订阅该版

请问在使用serial_v2的时候，这个问题正常吗？还是说我的理解存在错误？

原代码
```c
    static rt_size_t _serial_fifo_tx_blocking_buf(struct rt_device        *dev,
                                                     rt_off_t          pos,
                                               const void             *buffer,
                                                    rt_size_t          size)
    {
    struct rt_serial_device *serial;
    struct rt_serial_tx_fifo *tx_fifo = RT_NULL;

RT_ASSERT(dev != RT_NULL);
    if (size == 0) return 0;

serial = (struct rt_serial_device *)dev;
    RT_ASSERT((serial != RT_NULL) && (buffer != RT_NULL));
    tx_fifo = (struct rt_serial_tx_fifo *) serial->serial_tx;
    RT_ASSERT(tx_fifo != RT_NULL);
    /* When serial transmit in tx_blocking mode,
     * if the activated mode is RT_TRUE, it will return directly */
    if (tx_fifo->activated == RT_TRUE)  return 0;

tx_fifo->activated = RT_TRUE;
    rt_size_t length = size;
    rt_size_t offset = 0;

while (size)
    {
        /* Copy one piece of data into the ringbuffer at a time
         * until the length of the data is equal to size */
        tx_fifo->put_size = rt_ringbuffer_put(&(tx_fifo->rb),
                                               (rt_uint8_t *)buffer + offset,
                                               size);

offset += tx_fifo->put_size;
        size -= tx_fifo->put_size;
        /* Call the transmit interface for transmission */
        serial->ops->transmit(serial,
                             (rt_uint8_t *)buffer + offset,
                             tx_fifo->put_size,
                             RT_SERIAL_TX_BLOCKING);
        /* Waiting for the transmission to complete */
        rt_completion_wait(&(tx_fifo->tx_cpt), RT_WAITING_FOREVER);
    }

return length;
    }
```
异常点在于offset，尚未发送出去，就递增了。
```c
        offset += tx_fifo->put_size;
        size -= tx_fifo->put_size;
```
导致调用发送接口的时候，buffer + offset指针偏移的位置不正确。
```c
        serial->ops->transmit(serial,
                             (rt_uint8_t *)buffer + offset,
                             tx_fifo->put_size,
                             RT_SERIAL_TX_BLOCKING);
```

修改后代码，数据发送正常。
```c
    static rt_size_t _serial_fifo_tx_blocking_buf(struct rt_device        *dev,
                                                     rt_off_t          pos,
                                               const void             *buffer,
                                                    rt_size_t          size)
    {
    struct rt_serial_device *serial;
    struct rt_serial_tx_fifo *tx_fifo = RT_NULL;

RT_ASSERT(dev != RT_NULL);
    if (size == 0) return 0;

serial = (struct rt_serial_device *)dev;
    RT_ASSERT((serial != RT_NULL) && (buffer != RT_NULL));
    tx_fifo = (struct rt_serial_tx_fifo *) serial->serial_tx;
    RT_ASSERT(tx_fifo != RT_NULL);
    /* When serial transmit in tx_blocking mode,
     * if the activated mode is RT_TRUE, it will return directly */
    if (tx_fifo->activated == RT_TRUE)  return 0;

tx_fifo->activated = RT_TRUE;
    rt_size_t length = size;
    rt_size_t offset = 0;

while (size)
    {
        /* Copy one piece of data into the ringbuffer at a time
         * until the length of the data is equal to size */
        tx_fifo->put_size = rt_ringbuffer_put(&(tx_fifo->rb),
                                               (rt_uint8_t *)buffer + offset,
                                               size);

/* Call the transmit interface for transmission */
        serial->ops->transmit(serial,
                             (rt_uint8_t *)buffer + offset,
                             tx_fifo->put_size,
                             RT_SERIAL_TX_BLOCKING);
		
		offset += tx_fifo->put_size;
        size -= tx_fifo->put_size;
		
        /* Waiting for the transmission to complete */
        rt_completion_wait(&(tx_fifo->tx_cpt), RT_WAITING_FOREVER);
    }

return length;
    }
```