stm32+lwip(五):以太网帧发送测试

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系列文章：

stm32+lwip(一):使用STM32CubeMX生成项目

stm32+lwip(二):UDP测试

stm32+lwip(三):TCP测试

stm32+lwip(四):网页服务器测试

stm32+lwip(五):以太网帧发送测试

很多时候，我们想直接获取以太网帧的数据或者直接发送以太网帧数据。在使用STM32CubeMX生成的工程当中，有两个函数就是直接跟以太网通信有关：

 1 /**
 2  * This function should do the actual transmission of the packet. The packet is
 3  * contained in the pbuf that is passed to the function. This pbuf
 4  * might be chained.
 5  *
 6  * @param netif the lwip network interface structure for this ethernetif
 7  * @param p the MAC packet to send (e.g. IP packet including MAC addresses and type)
 8  * @return ERR_OK if the packet could be sent
 9  *         an err_t value if the packet couldn't be sent
10  *
11  * @note Returning ERR_MEM here if a DMA queue of your MAC is full can lead to
12  *       strange results. You might consider waiting for space in the DMA queue
13  *       to become availale since the stack doesn't retry to send a packet
14  *       dropped because of memory failure (except for the TCP timers).
15  */
16 
17 static err_t low_level_output(struct netif *netif, struct pbuf *p)

1 /**
2  * Should allocate a pbuf and transfer the bytes of the incoming
3  * packet from the interface into the pbuf.
4  *
5  * @param netif the lwip network interface structure for this ethernetif
6  * @return a pbuf filled with the received packet (including MAC header)
7  *         NULL on memory error
8    */
9 static struct pbuf * low_level_input(struct netif *netif)

这两个函数就是实现与以太网的通信，本来需要我们自己实现。现在STM32CubeMX已经帮我们实现好，因此收发以太网数据可以通过调用或修改这两个函数实现。

发送测试

  1 /**
  2   *****************************************************************************
  3   * @file    ethernet_test.c
  4   * @author  Zorb
  5   * @version V1.0.0
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