STM32F107上移植LWIP2.0.3　

因為最近需要在STM32F107上實現TCP/IP協議棧，所以網上查了一下，準備使用LWIP，雖然大多數用的是1.4.1版本但是官方說2系大版本修復了1.4.1的大量bug所以這裏用的版本是2.0.3，其實移植上沒有什麽太大區別。STM32F107集成了以太網媒體接入控制器MAC（主要負責控制和連接物理層的物理介質），所以按四層分層模型組成來看底層物理層組成還缺少一個物理接口收發器（PHY）。網上常見的應用於STM32上的PHY芯片有DP83848和LAN8720/LAN8700，開源電子網有關於LAN8720在LWIP上的移植應用，本質上兩個PHY的差別不是很大，只是在內部寄存器上有細小差別（因為PHY芯片的寄存器裏面的大部分寄存器是IEEE定義的）。說到這裏就要說一下MAC和PHY的關系，PHY把自己的目前的狀態反映到寄存器裏面,MAC通過SMI總線（物理接口是MII或RMII等）不斷的讀取PHY的狀態寄存器以得知目前PHY的狀態，當然也可以通過SMI設置PHY的寄存器達到控制的目的,例如流控的打開關閉,自協商模式還是強制模式等.不論是物理連接的MII總線和SMI總線還是PHY的狀態寄存器和控制寄存器都是有IEEE的規範的,因此不同公司的MAC和PHY一樣可以協調工作。

　　目前常見的MAC連接PHY的媒體獨立接口主要有MII，RMII， SMII，GMII等 ，在STM32F107上提供了兩種（RMII和MII）MAC連接PHY的物理接口，在應用不同的PHY芯片時，可以根據PHY芯片支持的類型選擇配置成不同的接口工作模式，在這裏我使用的是RMII即簡化的MII接口他需要的I/O是MII的一半（實際不止）。最後整體的物理層組成就是如下圖：

1，什麽是MAC？

MAC即Media Access Control,即媒體訪問控制子層協議。該協議位於OSI七層協議中數據鏈路層的下半部分,主要負責控制與連接物理層的物理介質.在發送數據的時候,MAC協議可以事先判斷是否可以發送數據,如果可以發送將給數據加上一些控制信息,最終將數據以及控制信息以規定的格式發送到物理層;在接收數據的時候,MAC協議首先判斷輸入的信息並是否發生傳輸錯誤,如果沒有錯誤,則去掉控制信息發送至網絡層.該層協議是以太網MAC由IEEE-802.3以太網標準定義.最新的MAC同時支持10Mbps和100Mbps兩種速率.

2，PHY什麽？

PHY是物理接口收發器,它實現物理層，PHY在發送數據的時候,收到MAC過來的數據(對PHY來說,沒有幀的概念,對它來說,都是數據而不管什麽地址,數據還是CRC.對於100BaseTX因為使用4B/5B編碼,每4bit就增加1bit的檢錯碼),然後把並行數據轉化為串行流數據,再按照物理層的編碼規則把數據編碼,再變為模擬信號把數據送出去.收數據時的流程反之.PHY還有個重要的功能就是實現CSMA/CD的部分功能.它可以檢測到網絡上是否有數據在傳送,如果有數據在傳送中就等待,一旦檢測到網絡空閑,再等待一個隨機時間後將送數據出去.如果兩個碰巧同時送出了數據,那樣必將造成沖突,這時候,沖突檢測機構可以檢測到沖突,然後各等待一個隨機的時間重新發送數據.這個隨機時間很有講究的,並不是一個常數,在不同的時刻計算出來的隨機時間都是不同的,而且有多重算法來應付出現概率很低的同兩臺主機之間的第二次沖突.

3，隔離變壓器

　　PHY和MAC是網卡的主要組成部分,網卡一般用RJ-45插口,10M網卡的RJ-45插口也只用了1,2,3,6四根針,而100M或1000M網卡的則是八根針都是全的。除此以外,還需要其它元件,因為雖然PHY提供絕大多數模擬支持,但在一個典型實現中,仍需外接6,7只分立元件及一個局域網絕緣模塊。絕緣模塊一般采用一個1：1的變壓器.這些部件的主要功能是為了保護PHY免遭由於電氣失誤而引起的損壞.一顆CMOS制程的芯片工作的時候產生的信號電平總是大於0V的(這取決於芯片的制程和設計需求),但是這樣的信號送到100米甚至更長的地方會有很大的直流分量的損失.而且如果外部網線直接和芯片相連的話,電磁感應(打雷)和靜電,很容易造成芯片的損壞.再就是設備接地方法不同,電網環境不同會導致雙方的0V電平不一致,這樣信號從A傳到B,由於A設備的0V電平和B點的0V電平不一樣,這樣會導致很大的電流從電勢高的設備流向電勢低的設備。為了解決以上問題隔離變壓器這個器件就應運而生.它把PHY送出來的差分信號用差模耦合的線圈耦合濾波以增強信號,並且通過電磁場的轉換耦合到連接網線的另外一端.這樣不但使網線和PHY之間沒有物理上的連接而換傳遞了信號,隔斷了信號中的直流分量,還可以在不同0V電平的設備中傳送數據.隔離變壓器本身就是設計為耐2KV~3KV的電壓的。

（以上內容參考這個鏈接的博主，他進行了非常極其全面的介紹關於物理層，看完大徹大悟呀推薦 http://www.cnblogs.com/jason-lu/articles/3195473.html）

　　繼續回到移植物理層上來說，在這裏以太網控制器的驅動代碼代碼參考ST官方的demo程序，但是如果物理層的芯片不同，驅動還是需要針對不同物理層PHY芯片進行細微改動（如果你是使用的DP83848芯片就不需要改），STM32支持RMll和Mll兩種MAC連接PHY芯片的總線接口，本次實驗使用的是DP83848作為PHY芯片采用RMII接口連接MAC層物理層驅動參考ST的DEMO程序。其實無論是那種芯片都可以使用這個demo程序進行移植，不同的PHY芯片可以通過修改一些宏來完成移植。

stm32_eth.h文件中詳細展示了針對不同PHY芯片所需要做的改動，如果你和文件中的兩種都不同可以通過芯片手冊查看確定。

 1 /** @defgroup PHY_status_register 
 2   * @{
 3   */ 
 4 /* The PHY status register value change from a PHY to another so the user have 
 5    to update this value depending on the used external PHY */
 6 /** 
 7   * @brief  For LAN8700  
 8   */ 
 9 //#define PHY_SR                           31         /*!< Tranceiver Status Register */
10 /** 
11   * @brief  For DP83848  
12   */ 
13 #define PHY_SR                           16     /*!< Tranceiver Status Register */
14 
15 /* The Speed and Duplex mask values change from a PHY to another so the user have to update
16    this value depending on the used external PHY */
17 /** 
18   * @brief  For LAN8700  
19   */ 
20 //#define PHY_Speed_Status            ((u16)0x0004)       /*!< Configured information of Speed: 10Mbps */
21 //#define PHY_Duplex_Status           ((u16)0x0010)       /*!< Configured information of Duplex: Full-duplex */
22 
23 /** 
24   * @brief  For DP83848  
25   */ 
26 #define PHY_Speed_Status            ((u16)0x0002)    /*!< Configured information of Speed: 10Mbps */
27 #define PHY_Duplex_Status           ((u16)0x0004)    /*!< Configured information of Duplex: Full-duplex */
28 #define IS_ETH_PHY_ADDRESS(ADDRESS) ((ADDRESS) <= 0x20)
29 #define IS_ETH_PHY_REG(REG) (((REG) == PHY_BCR) || 30                              ((REG) == PHY_BSR) || 31                              ((REG) == PHY_SR))

#define LAN8720_PHY_ADDRESS 0x00
#define DP83848_PHY_ADDRESS 0x01

其中最後兩個宏是我在其他地方借鑒過來的……。其實根據ST的demo程序移植物理層並不復雜，只需要進行簡單的修改就可以了，難點在於理解三個層（MAC，PHY，RJ45）的工作方式。最後最復雜的就是關於ST 的demo中關於DAM的哪一些操作，移植是基本不需要改動，但是要理解其工作方式，本人目前還是一頭霧水的這一部分可以看正點原子的F4的移植文檔。修改到這裏物理層就應該可以工作了。

　　接下來就是將物理層的數據交給IWIP協議棧內核了，在這裏LWIP在ethernetif.c中給我們提供了一個軟件框架沒有具體的實現，需要我們自己根據實際用用加入。

  1 /**
  2  * @file
  3  * Ethernet Interface Skeleton
  4  *
  5  */
  6 
  7 /*
  8  * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
  9  * All rights reserved.
 10  *
 11  * Redistribution and use in source and binary forms, with or without modification,
 12  * are permitted provided that the following conditions are met:
 13  *
 14  * 1. Redistributions of source code must retain the above copyright notice,
 15  *    this list of conditions and the following disclaimer.
 16  * 2. Redistributions in binary form must reproduce the above copyright notice,
 17  *    this list of conditions and the following disclaimer in the documentation
 18  *    and/or other materials provided with the distribution.
 19  * 3. The name of the author may not be used to endorse or promote products
 20  *    derived from this software without specific prior written permission.
 21  *
 22  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS‘‘ AND ANY EXPRESS OR IMPLIED
 23  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 24  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 25  * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 26  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 27  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 28  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 29  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 30  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 31  * OF SUCH DAMAGE.
 32  *
 33  * This file is part of the lwIP TCP/IP stack.
 34  *
 35  * Author: Adam Dunkels <[email protected]>
 36  *
 37  */
 38 
 39 /*
 40  * This file is a skeleton for developing Ethernet network interface
 41  * drivers for lwIP. Add code to the low_level functions and do a
 42  * search-and-replace for the word "ethernetif" to replace it with
 43  * something that better describes your network interface.
 44  */
 45 
 46 #include "lwip/opt.h"
 47 
 48 #if 0 /* don‘t build, this is only a skeleton, see previous comment */
 49 
 50 #include "lwip/def.h"
 51 #include "lwip/mem.h"
 52 #include "lwip/pbuf.h"
 53 #include "lwip/stats.h"
 54 #include "lwip/snmp.h"
 55 #include "lwip/ethip6.h"
 56 #include "lwip/etharp.h"
 57 #include "netif/ppp/pppoe.h"
 58 
 59 /* Define those to better describe your network interface. */
 60 #define IFNAME0 ‘e‘
 61 #define IFNAME1 ‘n‘
 62 
 63 /**
 64  * Helper struct to hold private data used to operate your ethernet interface.
 65  * Keeping the ethernet address of the MAC in this struct is not necessary
 66  * as it is already kept in the struct netif.
 67  * But this is only an example, anyway...
 68  */
 69 struct ethernetif {
 70   struct eth_addr *ethaddr;
 71   /* Add whatever per-interface state that is needed here. */
 72 };
 73 
 74 /* Forward declarations. */
 75 static void  ethernetif_input(struct netif *netif);
 76 
 77 /**
 78  * In this function, the hardware should be initialized.
 79  * Called from ethernetif_init().
 80  *
 81  * @param netif the already initialized lwip network interface structure
 82  *        for this ethernetif
 83  */
 84 static void
 85 low_level_init(struct netif *netif)
 86 {
 87   struct ethernetif *ethernetif = netif->state;
 88 
 89   /* set MAC hardware address length */
 90   netif->hwaddr_len = ETHARP_HWADDR_LEN;
 91 
 92   /* set MAC hardware address */
 93   netif->hwaddr[0] = ;
 94   ...
 95   netif->hwaddr[5] = ;
 96 
 97   /* maximum transfer unit */
 98   netif->mtu = 1500;
 99 
100   /* device capabilities */
101   /* don‘t set NETIF_FLAG_ETHARP if this device is not an ethernet one */
102   netif->flags = NETIF_FLAG_BROADCAST | NETIF_FLAG_ETHARP | NETIF_FLAG_LINK_UP;
103 
104 #if LWIP_IPV6 && LWIP_IPV6_MLD
105   /*
106    * For hardware/netifs that implement MAC filtering.
107    * All-nodes link-local is handled by default, so we must let the hardware know
108    * to allow multicast packets in.
109    * Should set mld_mac_filter previously. */
110   if (netif->mld_mac_filter != NULL) {
111     ip6_addr_t ip6_allnodes_ll;
112     ip6_addr_set_allnodes_linklocal(&ip6_allnodes_ll);
113     netif->mld_mac_filter(netif, &ip6_allnodes_ll, NETIF_ADD_MAC_FILTER);
114   }
115 #endif /* LWIP_IPV6 && LWIP_IPV6_MLD */
116 
117   /* Do whatever else is needed to initialize interface. */
118 }
119 
120 /**
121  * This function should do the actual transmission of the packet. The packet is
122  * contained in the pbuf that is passed to the function. This pbuf
123  * might be chained.
124  *
125  * @param netif the lwip network interface structure for this ethernetif
126  * @param p the MAC packet to send (e.g. IP packet including MAC addresses and type)
127  * @return ERR_OK if the packet could be sent
128  *         an err_t value if the packet couldn‘t be sent
129  *
130  * @note Returning ERR_MEM here if a DMA queue of your MAC is full can lead to
131  *       strange results. You might consider waiting for space in the DMA queue
132  *       to become available since the stack doesn‘t retry to send a packet
133  *       dropped because of memory failure (except for the TCP timers).
134  */
135 
136 static err_t
137 low_level_output(struct netif *netif, struct pbuf *p)
138 {
139   struct ethernetif *ethernetif = netif->state;
140   struct pbuf *q;
141 
142   initiate transfer();
143 
144 #if ETH_PAD_SIZE
145   pbuf_header(p, -ETH_PAD_SIZE); /* drop the padding word */
146 #endif
147 
148   for (q = p; q != NULL; q = q->next) {
149     /* Send the data from the pbuf to the interface, one pbuf at a
150        time. The size of the data in each pbuf is kept in the ->len
151        variable. */
152     send data from(q->payload, q->len);
153   }
154 
155   signal that packet should be sent();
156 
157   MIB2_STATS_NETIF_ADD(netif, ifoutoctets, p->tot_len);
158   if (((u8_t*)p->payload)[0] & 1) {
159     /* broadcast or multicast packet*/
160     MIB2_STATS_NETIF_INC(netif, ifoutnucastpkts);
161   } else {
162     /* unicast packet */
163     MIB2_STATS_NETIF_INC(netif, ifoutucastpkts);
164   }
165   /* increase ifoutdiscards or ifouterrors on error */
166 
167 #if ETH_PAD_SIZE
168   pbuf_header(p, ETH_PAD_SIZE); /* reclaim the padding word */
169 #endif
170 
171   LINK_STATS_INC(link.xmit);
172 
173   return ERR_OK;
174 }
175 
176 /**
177  * Should allocate a pbuf and transfer the bytes of the incoming
178  * packet from the interface into the pbuf.
179  *
180  * @param netif the lwip network interface structure for this ethernetif
181  * @return a pbuf filled with the received packet (including MAC header)
182  *         NULL on memory error
183  */
184 static struct pbuf *
185 low_level_input(struct netif *netif)
186 {
187   struct ethernetif *ethernetif = netif->state;
188   struct pbuf *p, *q;
189   u16_t len;
190 
191   /* Obtain the size of the packet and put it into the "len"
192      variable. */
193   len = ;
194 
195 #if ETH_PAD_SIZE
196   len += ETH_PAD_SIZE; /* allow room for Ethernet padding */
197 #endif
198 
199   /* We allocate a pbuf chain of pbufs from the pool. */
200   p = pbuf_alloc(PBUF_RAW, len, PBUF_POOL);
201 
202   if (p != NULL) {
203 
204 #if ETH_PAD_SIZE
205     pbuf_header(p, -ETH_PAD_SIZE); /* drop the padding word */
206 #endif
207 
208     /* We iterate over the pbuf chain until we have read the entire
209      * packet into the pbuf. */
210     for (q = p; q != NULL; q = q->next) {
211       /* Read enough bytes to fill this pbuf in the chain. The
212        * available data in the pbuf is given by the q->len
213        * variable.
214        * This does not necessarily have to be a memcpy, you can also preallocate
215        * pbufs for a DMA-enabled MAC and after receiving truncate it to the
216        * actually received size. In this case, ensure the tot_len member of the
217        * pbuf is the sum of the chained pbuf len members.
218        */
219       read data into(q->payload, q->len);
220     }
221     acknowledge that packet has been read();
222 
223     MIB2_STATS_NETIF_ADD(netif, ifinoctets, p->tot_len);
224     if (((u8_t*)p->payload)[0] & 1) {
225       /* broadcast or multicast packet*/
226       MIB2_STATS_NETIF_INC(netif, ifinnucastpkts);
227     } else {
228       /* unicast packet*/
229       MIB2_STATS_NETIF_INC(netif, ifinucastpkts);
230     }
231 #if ETH_PAD_SIZE
232     pbuf_header(p, ETH_PAD_SIZE); /* reclaim the padding word */
233 #endif
234 
235     LINK_STATS_INC(link.recv);
236   } else {
237     drop packet();
238     LINK_STATS_INC(link.memerr);
239     LINK_STATS_INC(link.drop);
240     MIB2_STATS_NETIF_INC(netif, ifindiscards);
241   }
242 
243   return p;
244 }
245 
246 /**
247  * This function should be called when a packet is ready to be read
248  * from the interface. It uses the function low_level_input() that
249  * should handle the actual reception of bytes from the network
250  * interface. Then the type of the received packet is determined and
251  * the appropriate input function is called.
252  *
253  * @param netif the lwip network interface structure for this ethernetif
254  */
255 static void
256 ethernetif_input(struct netif *netif)
257 {
258   struct ethernetif *ethernetif;
259   struct eth_hdr *ethhdr;
260   struct pbuf *p;
261 
262   ethernetif = netif->state;
263 
264   /* move received packet into a new pbuf */
265   p = low_level_input(netif);
266   /* if no packet could be read, silently ignore this */
267   if (p != NULL) {
268     /* pass all packets to ethernet_input, which decides what packets it supports */
269     if (netif->input(p, netif) != ERR_OK) {
270       LWIP_DEBUGF(NETIF_DEBUG, ("ethernetif_input: IP input error\n"));
271       pbuf_free(p);
272       p = NULL;
273     }
274   }
275 }
276 
277 /**
278  * Should be called at the beginning of the program to set up the
279  * network interface. It calls the function low_level_init() to do the
280  * actual setup of the hardware.
281  *
282  * This function should be passed as a parameter to netif_add().
283  *
284  * @param netif the lwip network interface structure for this ethernetif
285  * @return ERR_OK if the loopif is initialized
286  *         ERR_MEM if private data couldn‘t be allocated
287  *         any other err_t on error
288  */
289 err_t
290 ethernetif_init(struct netif *netif)
291 {
292   struct ethernetif *ethernetif;
293 
294   LWIP_ASSERT("netif != NULL", (netif != NULL));
295 
296   ethernetif = mem_malloc(sizeof(struct ethernetif));
297   if (ethernetif == NULL) {
298     LWIP_DEBUGF(NETIF_DEBUG, ("ethernetif_init: out of memory\n"));
299     return ERR_MEM;
300   }
301 
302 #if LWIP_NETIF_HOSTNAME
303   /* Initialize interface hostname */
304   netif->hostname = "lwip";
305 #endif /* LWIP_NETIF_HOSTNAME */
306 
307   /*
308    * Initialize the snmp variables and counters inside the struct netif.
309    * The last argument should be replaced with your link speed, in units
310    * of bits per second.
311    */
312   MIB2_INIT_NETIF(netif, snmp_ifType_ethernet_csmacd, LINK_SPEED_OF_YOUR_NETIF_IN_BPS);
313 
314   netif->state = ethernetif;
315   netif->name[0] = IFNAME0;
316   netif->name[1] = IFNAME1;
317   /* We directly use etharp_output() here to save a function call.
318    * You can instead declare your own function an call etharp_output()
319    * from it if you have to do some checks before sending (e.g. if link
320    * is available...) */
321   netif->output = etharp_output;
322 #if LWIP_IPV6
323   netif->output_ip6 = ethip6_output;
324 #endif /* LWIP_IPV6 */
325   netif->linkoutput = low_level_output;
326 
327   ethernetif->ethaddr = (struct eth_addr *)&(netif->hwaddr[0]);
328 
329   /* initialize the hardware */
330   low_level_init(netif);
331 
332   return ERR_OK;
333 }
334 
335 #endif /* 0 */

IWIP內核和底層物理層數據交互只需要如下幾個函數

low_level_init

負責底層MAC地址的配置，MTU和網卡支持的功能和網卡的註冊和使能相關，這個函數有LWIP內核初始化由ethernetif_init調用。

low_level_input

接受以太網數據幀，最後由ethernetif_input函數調用輸入IWIP內核處理。

low_level_output

內核由需要發送的數據將最終調用這個函數交給物理層發送。以上三個函數的具體實現ST的demo程序已經完成了，直接拿來就可以是用了。

最終代碼：

static void
low_level_init(struct netif *netif)
{
  /* set MAC hardware address length */
  netif->hwaddr_len = ETHARP_HWADDR_LEN;

  /* set MAC hardware address */
  netif->hwaddr[0] =  MACaddr[0];
  netif->hwaddr[1] =  MACaddr[1];
  netif->hwaddr[2] =  MACaddr[2];
  netif->hwaddr[3] =  MACaddr[3];
  netif->hwaddr[4] =  MACaddr[4];
  netif->hwaddr[5] =  MACaddr[5];

  /* maximum transfer unit */
  netif->mtu = 1500;

  /* device capabilities */
  /* don‘t set NETIF_FLAG_ETHARP if this device is not an ethernet one */
  netif->flags = NETIF_FLAG_BROADCAST | NETIF_FLAG_ETHARP | NETIF_FLAG_LINK_UP;

  /* Initialize Tx Descriptors list: Chain Mode */
  ETH_DMATxDescChainInit(DMATxDscrTab, &Tx_Buff[0][0], ETH_TXBUFNB);
  /* Initialize Rx Descriptors list: Chain Mode  */
  ETH_DMARxDescChainInit(DMARxDscrTab, &Rx_Buff[0][0], ETH_RXBUFNB);

  /* Enable Ethernet Rx interrrupt */
  { int i;
    for(i=0; i<ETH_RXBUFNB; i++)
    {
      ETH_DMARxDescReceiveITConfig(&DMARxDscrTab[i], ENABLE);
    }
  }

#ifdef CHECKSUM_BY_HARDWARE
  /* Enable the checksum insertion for the Tx frames */
  { int i;
    for(i=0; i<ETH_TXBUFNB; i++)
    {
      ETH_DMATxDescChecksumInsertionConfig(&DMATxDscrTab[i], ETH_DMATxDesc_ChecksumTCPUDPICMPFull);
    }
  }
#endif

  /* Enable MAC and DMA transmission and reception */
  ETH_Start();

}

static err_t
low_level_output(struct netif *netif, struct pbuf *p)
{
  struct pbuf *q;
  int l = 0;
  u8 *buffer =  (u8 *)ETH_GetCurrentTxBuffer();
  
  for(q = p; q != NULL; q = q->next) 
  {
    memcpy((u8_t*)&buffer[l], q->payload, q->len);
    l = l + q->len;
  }

  ETH_TxPkt_ChainMode(l);

  return ERR_OK;
}

static struct pbuf *
low_level_input(struct netif *netif)
{
  struct pbuf *p, *q;
  u16_t len;
  int l =0;
  FrameTypeDef frame;
  u8 *buffer;
  
  p = NULL;
  frame = ETH_RxPkt_ChainMode();  
  /* Obtain the size of the packet and put it into the "len"
     variable. */
  len = frame.length;
  
  buffer = (u8 *)frame.buffer;

  /* We allocate a pbuf chain of pbufs from the pool. */
  p = pbuf_alloc(PBUF_RAW, len, PBUF_POOL);

  if (p != NULL)
  {
    for (q = p; q != NULL; q = q->next)
    {
      memcpy((u8_t*)q->payload, (u8_t*)&buffer[l], q->len);
      l = l + q->len;
    }    
  }


  /* Set Own bit of the Rx descriptor Status: gives the buffer back to ETHERNET DMA */
  frame.descriptor->Status = ETH_DMARxDesc_OWN; 
 
  /* When Rx Buffer unavailable flag is set: clear it and resume reception */
  if ((ETH->DMASR & ETH_DMASR_RBUS) != (u32)RESET)  
  {
    /* Clear RBUS ETHERNET DMA flag */
    ETH->DMASR = ETH_DMASR_RBUS;
    /* Resume DMA reception */
    ETH->DMARPDR = 0;
  }


  return p;
}

這樣底層移植算基本完成了，如果配置了以太網中斷則需要在中斷中放入如下代碼

/* Handles all the received frames */
  while(ETH_GetRxPktSize() != 0) 
  {        
    LwIP_Pkt_Handle();//TODO FOR COMPILE MXC
  }

  /* Clear the Eth DMA Rx IT pending bits */
  ETH_DMAClearITPendingBit(ETH_DMA_IT_R);
  ETH_DMAClearITPendingBit(ETH_DMA_IT_NIS);

這樣就可以將底層數據遞交到網絡層了，其中LWIP_Pkt_Handle()只是針對ethernetif_input函數的一個簡單封裝，如果為配置為查詢模式，只需要將LWIP_Pkt_Handle()放在主循環中查詢調用就可以了。完事了接下來。。。此時如果沒有問題對MAC地址，IP地址和網關等一系列的內容進行配置後就應該能ping通了。

STM32F107移植LWIP