1. 前言

在STM32平台移植LWIP 2.1.2功能，首先需要做一些准备工作，例如：

下载资料：lwip-2.1.2、contrib-2.1.0、STM32F4x7_ETH_LwIP_V1.1.1，参考：《基于STM32移植LWIP的资料准备》
准备好已经在STM32移植好的FreeRTOS的工程。

移植的目标平台是STM32F429，在以前资料准备中有提到STM32官网有STM32F4x7微控制器的LwIP TCP/IP协议栈的演示代码，我们在很大程度上可以参考移植到目标平台。

2. STM32运行LwIP的系统框图

我们在STM32平台上面移植LwIP，主要完成以下4个部分：

RTOS：在STM32运行FreeRTOS，并且为LwIP协议栈提供Mutex、Mail box和Create Thread等API接口。
Network System Config：主要对LwIP协议栈的系统设置。
LwIP Stack：这个是LwIP 2.1.2 TCP/IP协议栈，我们只需要将源码添加到工程即可。
Hardware Driver：主要是STM32平台ETH接口的驱动层，例如：GPIOs, clocks, MAC, DMA的设置。

这4个部分之间的联系框图如下：

3. LwIP RTOS部分的移植

在LwIP RTOS部分的移植我们可以参考contrib-2.1.0，这部分主要是为LwIP协议栈提供Mutex、Mail box和Create Thread等API接口。因为每个OS对这些API接口的具体实现都会有差异，所以LwIP官方提供了一个模板。正好contrib-2.1.0里面有提供FreeRTOS这些接口的实现，我们可以直接移植过来，代码路径如下：
PATH：contrib-2.1.0\ports\freertos\sys_arch.c

RTOS提供提供架构的接口，如下：

4. LwIP System Config部分的移植

在LwIP System Config部分的移植我们可以参考STM32F4x7_ETH_LwIP_V1.1.1（PATH: STM32F4x7_ETH_LwIP_V1.1.1\Project\FreeRTOS\udptcp_echo_server_netconn\src\netconf.c），主要的步骤如下：

tcpip_init()：主要是创建tcp_ip stack线程，并且调用lwip_init()函数初始化LwIP协议栈。
netif_add()：申请一个struct netif，设置默认的IP地址、子网掩码和网关，并且将其网络接口添加到netif_list。
netif_set_default()：注册新申请的网络接口为默认网络接口。
netif_set_up()：启动网络接口。
dhcp_start()：开始DHCP自动获取IP地址，如果设置默认IP地址，可不调用。（备注：非必须调用）

LwIP System Config还有一个更重要部分，就是LwIP系统选项配置的头文件lwipopts.h。我这里的配置如下：（仅供参考）

#ifndef __LWIPOPTS_H__
#define __LWIPOPTS_H__

/**
 * SYS_LIGHTWEIGHT_PROT==1: if you want inter-task protection for certain
 * critical regions during buffer allocation, deallocation and memory
 * allocation and deallocation.
 */
#define SYS_LIGHTWEIGHT_PROT    0

#define ETHARP_TRUST_IP_MAC     0
#define IP_REASSEMBLY           0
#define IP_FRAG                 0
#define ARP_QUEUEING            0

#define LWIP_IPV4               1

/**
 * NO_SYS==1: Provides VERY minimal functionality. Otherwise,
 * use lwIP facilities.
 */
#define NO_SYS                  0

/* ---------- Memory options ---------- */
/* MEM_ALIGNMENT: should be set to the alignment of the CPU for which
   lwIP is compiled. 4 byte alignment -> define MEM_ALIGNMENT to 4, 2
   byte alignment -> define MEM_ALIGNMENT to 2. */
#define MEM_ALIGNMENT           4

/* MEM_SIZE: the size of the heap memory. If the application will send
a lot of data that needs to be copied, this should be set high. */
#define MEM_SIZE                (5*1024)

/* MEMP_NUM_PBUF: the number of memp struct pbufs. If the application
   sends a lot of data out of ROM (or other static memory), this
   should be set high. */
#define MEMP_NUM_PBUF           100
/* MEMP_NUM_UDP_PCB: the number of UDP protocol control blocks. One
   per active UDP "connection". */
#define MEMP_NUM_UDP_PCB        6
/* MEMP_NUM_TCP_PCB: the number of simulatenously active TCP
   connections. */
#define MEMP_NUM_TCP_PCB        10
/* MEMP_NUM_TCP_PCB_LISTEN: the number of listening TCP
   connections. */
#define MEMP_NUM_TCP_PCB_LISTEN 5
/* MEMP_NUM_TCP_SEG: the number of simultaneously queued TCP
   segments. */
#define MEMP_NUM_TCP_SEG        20
/* MEMP_NUM_SYS_TIMEOUT: the number of simulateously active
   timeouts. */
#define MEMP_NUM_SYS_TIMEOUT    10


/* ---------- Pbuf options ---------- */
/* PBUF_POOL_SIZE: the number of buffers in the pbuf pool. */
#define PBUF_POOL_SIZE          20

/* PBUF_POOL_BUFSIZE: the size of each pbuf in the pbuf pool. */
#define PBUF_POOL_BUFSIZE       500


/* ---------- TCP options ---------- */
#define LWIP_TCP                1
#define TCP_TTL                 255

/* Controls if TCP should queue segments that arrive out of
   order. Define to 0 if your device is low on memory. */
#define TCP_QUEUE_OOSEQ         0

/* TCP Maximum segment size. */
#define TCP_MSS                 (1500 - 40)	  /* TCP_MSS = (Ethernet MTU - IP header size - TCP header size) */

/* TCP sender buffer space (bytes). */
#define TCP_SND_BUF             (5*TCP_MSS)

/*  TCP_SND_QUEUELEN: TCP sender buffer space (pbufs). This must be at least
  as much as (2 * TCP_SND_BUF/TCP_MSS) for things to work. */

#define TCP_SND_QUEUELEN        (4* TCP_SND_BUF/TCP_MSS)

/* TCP receive window. */
#define TCP_WND                 (2*TCP_MSS)


/* ---------- ICMP options ---------- */
#define LWIP_ICMP                       1


/* ---------- DHCP options ---------- */
/* Define LWIP_DHCP to 1 if you want DHCP configuration of
   interfaces. DHCP is not implemented in lwIP 0.5.1, however, so
   turning this on does currently not work. */
#define LWIP_DHCP               1


/* ---------- UDP options ---------- */
#define LWIP_UDP                1
#define UDP_TTL                 255


/* ---------- Statistics options ---------- */
#define LWIP_STATS 0
#define LWIP_PROVIDE_ERRNO 1

/* ---------- link callback options ---------- */
/* LWIP_NETIF_LINK_CALLBACK==1: Support a callback function from an interface
 * whenever the link changes (i.e., link down)
 */
#define LWIP_NETIF_LINK_CALLBACK        1

/*
   --------------------------------------
   ---------- Checksum options ----------
   --------------------------------------
*/

/* 
The STM32F4x7 allows computing and verifying the IP, UDP, TCP and ICMP checksums by hardware:
 - To use this feature let the following define uncommented.
 - To disable it and process by CPU comment the  the checksum.
*/
#define CHECKSUM_BY_HARDWARE 


#ifdef CHECKSUM_BY_HARDWARE
  /* CHECKSUM_GEN_IP==0: Generate checksums by hardware for outgoing IP packets.*/
  #define CHECKSUM_GEN_IP                 0
  /* CHECKSUM_GEN_UDP==0: Generate checksums by hardware for outgoing UDP packets.*/
  #define CHECKSUM_GEN_UDP                0
  /* CHECKSUM_GEN_TCP==0: Generate checksums by hardware for outgoing TCP packets.*/
  #define CHECKSUM_GEN_TCP                0 
  /* CHECKSUM_CHECK_IP==0: Check checksums by hardware for incoming IP packets.*/
  #define CHECKSUM_CHECK_IP               0
  /* CHECKSUM_CHECK_UDP==0: Check checksums by hardware for incoming UDP packets.*/
  #define CHECKSUM_CHECK_UDP              0
  /* CHECKSUM_CHECK_TCP==0: Check checksums by hardware for incoming TCP packets.*/
  #define CHECKSUM_CHECK_TCP              0
  /* CHECKSUM_CHECK_ICMP==0: Check checksums by hardware for incoming ICMP packets.*/
  #define CHECKSUM_GEN_ICMP               0
#else
  /* CHECKSUM_GEN_IP==1: Generate checksums in software for outgoing IP packets.*/
  #define CHECKSUM_GEN_IP                 1
  /* CHECKSUM_GEN_UDP==1: Generate checksums in software for outgoing UDP packets.*/
  #define CHECKSUM_GEN_UDP                1
  /* CHECKSUM_GEN_TCP==1: Generate checksums in software for outgoing TCP packets.*/
  #define CHECKSUM_GEN_TCP                1
  /* CHECKSUM_CHECK_IP==1: Check checksums in software for incoming IP packets.*/
  #define CHECKSUM_CHECK_IP               1
  /* CHECKSUM_CHECK_UDP==1: Check checksums in software for incoming UDP packets.*/
  #define CHECKSUM_CHECK_UDP              1
  /* CHECKSUM_CHECK_TCP==1: Check checksums in software for incoming TCP packets.*/
  #define CHECKSUM_CHECK_TCP              1
  /* CHECKSUM_CHECK_ICMP==1: Check checksums by hardware for incoming ICMP packets.*/
  #define CHECKSUM_GEN_ICMP               1
#endif


/*
   ----------------------------------------------
   ---------- Sequential layer options ----------
   ----------------------------------------------
*/
/**
 * LWIP_NETCONN==1: Enable Netconn API (require to use api_lib.c)
 */
#define LWIP_NETCONN                    1

/*
   ------------------------------------
   ---------- Socket options ----------
   ------------------------------------
*/
/**
 * LWIP_SOCKET==1: Enable Socket API (require to use sockets.c)
 */
#define LWIP_SOCKET                     0

/*
   -----------------------------------
   ---------- DEBUG options ----------
   -----------------------------------
*/

#define LWIP_DEBUG                      0


/*
   ---------------------------------
   ---------- OS options ----------
   ---------------------------------
*/

#define TCPIP_THREAD_NAME              "TCP/IP"
#define TCPIP_THREAD_STACKSIZE          1000
#define TCPIP_MBOX_SIZE                 5
#define DEFAULT_UDP_RECVMBOX_SIZE       2000
#define DEFAULT_TCP_RECVMBOX_SIZE       2000
#define DEFAULT_ACCEPTMBOX_SIZE         2000
#define DEFAULT_THREAD_STACKSIZE        500
#define TCPIP_THREAD_PRIO               3 

//#define LWIP_COMPAT_MUTEX 1

#endif /* __LWIPOPTS_H__ */

5. LwIP Stack部分的移植

将LwIP 2.1.2的源码添加到工程，分别为api、core、netif，详细如下：

将LwIP 2.1.2的头文件路径添加到Keil：

6. LwIP Hardware Driver部分的移植

LwIP Hardware Driver部分的移植主要是2个文件，如下：

bsp_eth.c：主要是设置Ethernet的GPIOs, clocks, MAC, DMA，参考：STM32F4x7_ETH_LwIP_V1.1.1\Project\FreeRTOS\udptcp_echo_server_netconn\src\stm32f4x7_eth_bsp.c
ethernetif.c：主要是创建了一个ETH_MAC线程，读取以太网的消息。low_level_input收到消息后，然后通过call back调用ethernet_input传递到LwIP层去解析。如果LwIP层有消息需要发送，就通过ethernet_output调用ETH Hardware Driver层的low_level_output发送出去。参考：STM32F4x7_ETH_LwIP_V1.1.1\Utilities\Third_Party\lwip-1.4.1\port\STM32F4x7\FreeRTOS\ethernetif.c