【无OS】基于STM32移植LWIP 1.4.1之DHCP

1.前言

本篇文章介绍在STM32平台移植LwIP DHCP，是基于对DHCP协议工作过程有一定了解后，再在以前实现Ping功能的基础上来实现的。所以在阅读本文之前，可能需要参考一下以前写的文章：

1. 《DHCP协议工作流程分析》
2. 《【无OS】基于STM32移植LWIP 1.4.1之Ping》

由于有之前实现Ping功能的基础，所以DHCP的移植很简单，下面将主要介绍LwIP DHCP的流程分析。

2.DHCP功能的移植

LwIP模式已经实现了DHCP客户端的功能，我们只需要打开相关宏就可以。修改如下：

--- a/stm32f429_lwip_basic_ping/User/LAN8742A/netconf.h
+++ b/stm32f429_lwip_basic_ping/User/LAN8742A/netconf.h
@@ -41,6 +41,9 @@
 #define DHCP_ADDRESS_ASSIGNED      3
 #define DHCP_TIMEOUT               4
 #define DHCP_LINK_DOWN             5
+
+#define USE_DHCP       /* enable DHCP, if disabled static address is used */
+
 /* Exported constants --------------------------------------------------------*/
 /* Exported macro ------------------------------------------------------------*/
 /* Exported functions ------------------------------------------------------- */

编译成功后，验证结果截图如下：

3.打印LwIP DHCP Log

为了方便熟悉LwIP DHCP工作流程，需要打印DHCP Log来分析。这里打开了3个宏：

1. LWIP_DEBUG
2. UDP_DEBUG
3. DHCP_DEBUG

修改代码如下：

--- a/stm32f429_lwip_pro_list/2.stm32f429_lwip_basic_dhcp/User/lwipopts.h
+++ b/stm32f429_lwip_pro_list/2.stm32f429_lwip_basic_dhcp/User/lwipopts.h
@@ -209,7 +209,7 @@ The STM32F4x7 allows computing and verifying the IP, UDP, TCP and ICMP checksums
    ---------- Lwip Debug options ----------
    ----------------------------------------
 */
-//#define LWIP_DEBUG                      1
+#define LWIP_DEBUG                      1

 #endif /* __LWIPOPTS_H__ */

--- a/stm32f429_lwip_pro_list/2.stm32f429_lwip_basic_dhcp/lwip-1.4.1/src/include/lwip/opt.h
+++ b/stm32f429_lwip_pro_list/2.stm32f429_lwip_basic_dhcp/lwip-1.4.1/src/include/lwip/opt.h
@@ -2071,7 +2071,7 @@
  * UDP_DEBUG: Enable debugging in UDP.
  */
 #ifndef UDP_DEBUG
-#define UDP_DEBUG                       LWIP_DBG_OFF
+#define UDP_DEBUG                       LWIP_DBG_ON
 #endif

 /**
@@ -2099,7 +2099,7 @@
  * DHCP_DEBUG: Enable debugging in dhcp.c.
  */
 #ifndef DHCP_DEBUG
-#define DHCP_DEBUG                      LWIP_DBG_OFF
+#define DHCP_DEBUG                      LWIP_DBG_ON
 #endif

4.LwIP DHCP工作过程

LwIP DHCP工作过程主要包括4个阶段，如下：

1. 发现阶段（DHCP Discover）：即 DHCP 客户端寻找 DHCP 服务器的阶段。
2. 提供阶段（DHCP Offer）：即 DHCP 服务器提供 IP 地址的阶段。
3. 选择阶段（DHCP Request）：即 DHCP 客户端选择某台 DHCP 服务器提供的 IP 地址的阶段。
4. 确认阶段（DHCP Ack）：即 DHCP 服务器确认所提供的 IP 地址的阶段。

下面根据代码和log分析一下这4个阶段。

4.1 发现阶段（DHCP Discover）

调用了dhcp_start函数后，就开启了DHCP的流程。主要是通过UDP与DHCP Sever通信。在发现阶段，DHCP客户端通过发送DHCP-DISCOVER报文来寻找DHCP服务器。由于DHCP服务器的IP地址对于客户端来说是未知的，所以DHCP客户端以广播方式发送DHCP-DISCOVER报文。设备的打印Log如下：

[12:52:08.025]dhcp_start(netif=20003e7c) st0
[12:52:08.026]dhcp_start(): starting new DHCP client
[12:52:08.038]dhcp_start(): allocated dhcpudp_bind(ipaddr = 0.0.0.0, port = 68)
[12:52:08.038]udp_bind: bound to 0.0.0.0, port 68
[12:52:08.039]udp_connect: connected to 0.0.0.0,port 68
[12:52:08.040]dhcp_start(): starting DHCP configuration
[12:52:08.050]dhcp_discover()
[12:52:08.051]transaction id xid(abcd0001)
[12:52:08.052]dhcp_discover: making request
[12:52:08.052]dhcp_discover: realloc()ing
[12:52:08.060]dhcp_discover: sendto(DISCOVER, IP_ADDR_BROADCAST, DHCP_SERVER_PORT)
[12:52:08.066]udp_send: added header in given pbuf 20003f34
[12:52:08.072]udp_send: sending datagram of length 316
[12:52:08.073]udp_send: UDP packet length 316
[12:52:08.074]udp_send: UDP checksum 0x0000
[12:52:08.075]udp_send: ip_output_if (,,,,IP_PROTO_UDP,)
[12:52:08.085]dhcp_discover: deleting()ing
[12:52:08.086]dhcp_discover: SELECTING
[12:52:08.086]dhcp_discover(): set request timeout 2000 msecs

根据设备的打印log，然后结合代码整理出DHCP Discover的时序图如下：

4.2 提供阶段（DHCP Offer）

网络中接收到DHCP-DISCOVER报文的DHCP服务器，会选择一个合适的IP地址，连同IP地址租约期限和其他配置信息（如网关地址，域名服务器地址等）一同通过DHCP-OFFER报文发送给DHCP客户端。设备的打印Log如下：

[12:52:08.093]udp_input: received datagram of length 556
[12:52:08.093]UDP header:
[12:52:08.094]+-------------------------------+
[12:52:08.106]|        67     |        68     | (src port, dest port)
[12:52:08.106]+-------------------------------+
[12:52:08.107]|       556     |     0x6d50    | (len, chksum)
[12:52:08.116]+-------------------------------+
[12:52:08.117]udp (192.168.1.102, 68) <-- (192.168.1.1, 67)
[12:52:08.118]udp_input: calculating checksum
[12:52:08.128]dhcp_recv(pbuf = 200086fc) from DHCP server 192.168.1.1 port 67
[12:52:08.128]pbuf->len = 458
[12:52:08.129]pbuf->tot_len = 548
[12:52:08.130]searching DHCP_OPTION_MESSAGE_TYPE
[12:52:08.138]DHCP_OFFER received in DHCP_SELECTING state
[12:52:08.138]dhcp_handle_offer(netif=20003e7c) st0
[12:52:08.139]dhcp_handle_offer(): server 0x0101a8c0
[12:52:08.149]dhcp_handle_offer(): offer for 0x6601a8c0

根据设备的打印log，然后结合代码整理出DHCP Offer的时序图如下：

4.3 选择阶段（DHCP Request）

在选择阶段，如果有多台DHCP服务器向DHCP客户端回应DHCP-OFFER报文，则DHCP客户端只接受第一个收到的DHCP-OFFER报文。然后以广播方式发送DHCP-REQUEST请求报文，该报文中包含Option 54（服务器标识选项），即它选择的DHCP服务器的IP地址信息。设备的打印Log如下：

[12:52:08.150]dhcp_select(netif=20003e7c) st0
[12:52:08.150]transaction id xid(abcd0002)
[12:52:08.151]udp_send: added header in given pbuf 20003f34
[12:52:08.160]udp_send: sending datagram of length 316
[12:52:08.161]udp_send: UDP packet length 316
[12:52:08.161]udp_send: UDP checksum 0x0000
[12:52:08.171]udp_send: ip_output_if (,,,,IP_PROTO_UDP,)
[12:52:08.171]dhcp_select: REQUESTING
[12:52:08.172]dhcp_select(): set request timeout 2000 msecs

根据设备的打印log，然后结合代码整理出DHCP Request的时序图如下：

4.4确认阶段（DHCP Ack）

收到DHCP客户端发送的DHCP-REQUEST请求报文后，DHCP服务器根据DHCP-REQUEST报文中携带的MAC地址来查找有没有相应的租约记录。如果有，则发送DHCP-ACK报文作为应答，通知DHCP客户端可以使用分配的IP地址。设备的打印Log如下：

[12:52:08.173]udp_input: received datagram of length 556
[12:52:08.180]UDP header:
[12:52:08.181]+-------------------------------+
[12:52:08.181]|        67     |        68     | (src port, dest port)
[12:52:08.192]+-------------------------------+
[12:52:08.193]|       556     |     0x544f    | (len, chksum)
[12:52:08.194]+-------------------------------+
[12:52:08.203]udp (192.168.1.102, 68) <-- (192.168.1.1, 67)
[12:52:08.203]udp_input: calculating checksum
[12:52:08.204]dhcp_recv(pbuf = 200084f8) from DHCP server 192.168.1.1 port 67
[12:52:08.205]pbuf->len = 458
[12:52:08.214]pbuf->tot_len = 548
[12:52:08.215]searching DHCP_OPTION_MESSAGE_TYPE
[12:52:08.215]DHCP_ACK received

根据设备的打印log，然后结合代码整理出DHCP Ack的时序图如下：

5.dhcp_start函数分析

dhcp_start函数主要作用是：为网络接口启动DHCP协商，根据dhcp_start源码总结主要流程如下：

dhcp_start函数的源码如下：（备注：为方便分析主要流程，其中代码有删减）

err_t
dhcp_start(struct netif *netif)
{
    
    
	......
	
  /* check hwtype of the netif */
  if ((netif->flags & NETIF_FLAG_ETHARP) == 0) {
    
    
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): No ETHARP netif\n"));
    return ERR_ARG;
  }

  /* check MTU of the netif */
  if (netif->mtu < DHCP_MAX_MSG_LEN_MIN_REQUIRED) {
    
    
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): Cannot use this netif with DHCP: MTU is too small\n"));
    return ERR_MEM;
  }

  /* no DHCP client attached yet? */
  LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): starting new DHCP client\n"));
  dhcp = (struct dhcp *)mem_malloc(sizeof(struct dhcp));

  /* store this dhcp client in the netif */
  netif->dhcp = dhcp;
  LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): allocated dhcp"));
    
  /* clear data structure */
  memset(dhcp, 0, sizeof(struct dhcp));
  /* dhcp_set_state(&dhcp, DHCP_OFF); */
  /* allocate UDP PCB */
  dhcp->pcb = udp_new();
  
  ip_set_option(dhcp->pcb, SOF_BROADCAST);
  /* set up local and remote port for the pcb */
  udp_bind(dhcp->pcb, IP_ADDR_ANY, DHCP_CLIENT_PORT);
  udp_connect(dhcp->pcb, IP_ADDR_ANY, DHCP_SERVER_PORT);
  /* set up the recv callback and argument */
  udp_recv(dhcp->pcb, dhcp_recv, netif);
  LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): starting DHCP configuration\n"));
  /* (re)start the DHCP negotiation */
  result = dhcp_discover(netif);

  /* Set the flag that says this netif is handled by DHCP. */
  netif->flags |= NETIF_FLAG_DHCP;
  return result;
}

6.dhcp_recv函数分析

dhcp_recv函数主要作用是：如果传入的DHCP消息是属于本设备的响应，则触发对应的状态机。根据dhcp_recv源码总结主要流程如下：

dhcp_recv函数的源码如下：（备注：为方便分析主要流程，其中代码有删减）

static void
dhcp_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, ip_addr_t *addr, u16_t port)
{
    
    
	......

  if (reply_msg->op != DHCP_BOOTREPLY) {
    
    
    goto free_pbuf_and_return;
  }
  /* iterate through hardware address and match against DHCP message */
  for (i = 0; i < netif->hwaddr_len; i++) {
    
    
    if (netif->hwaddr[i] != reply_msg->chaddr[i]) {
    
    
      goto free_pbuf_and_return;
    }
  }
  /* match transaction ID against what we expected */
  if (ntohl(reply_msg->xid) != dhcp->xid) {
    
    
    goto free_pbuf_and_return;
  }
  /* option fields could be unfold? */
  if (dhcp_parse_reply(dhcp, p) != ERR_OK) {
    
    
    goto free_pbuf_and_return;
  }

  LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("searching DHCP_OPTION_MESSAGE_TYPE\n"));
  /* obtain pointer to DHCP message type */
  if (!dhcp_option_given(dhcp, DHCP_OPTION_IDX_MSG_TYPE)) {
    
    
    goto free_pbuf_and_return;
  }

  /* read DHCP message type */
  msg_type = (u8_t)dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_MSG_TYPE);
  /* message type is DHCP ACK? */
  if (msg_type == DHCP_ACK) {
    
    
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_ACK received\n"));
    /* in requesting state? */
    if (dhcp->state == DHCP_REQUESTING) {
    
    
      dhcp_handle_ack(netif);
	  ......
    }
	......
  }
  /* received a DHCP_NAK in appropriate state? */
  else if ((msg_type == DHCP_NAK) &&
    ((dhcp->state == DHCP_REBOOTING) || (dhcp->state == DHCP_REQUESTING) ||
     (dhcp->state == DHCP_REBINDING) || (dhcp->state == DHCP_RENEWING  ))) {
    
    
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_NAK received\n"));
    dhcp_handle_nak(netif);
  }
  /* received a DHCP_OFFER in DHCP_SELECTING state? */
  else if ((msg_type == DHCP_OFFER) && (dhcp->state == DHCP_SELECTING)) {
    
    
    LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_OFFER received in DHCP_SELECTING state\n"));
    dhcp->request_timeout = 0;
    /* remember offered lease */
    dhcp_handle_offer(netif);
  }
  
free_pbuf_and_return:
  dhcp->msg_in = NULL;
  pbuf_free(p);
}

7.资料下载地址

移植成功的完整代码下载地址如下：
https://download.csdn.net/download/ZHONGCAI0901/12959157
资料里面主要是移植成功的完整代码，在2.stm32f429_lwip_basic_dhcp\Doc目录下有分析过程中所用到的资料，如下：