首先需要將默認網絡地址信息結構體中的模式改為DHCP模式

/* network information */
wiz_NetInfo default_net_info = {
   .mac  = {0x00, 0x08, 0xdc, 0x12, 0x22, 0x12},
   .ip   = {192, 168, 1, 30},
   .gw   = {192, 168, 1, 1},
   .sn   = {255, 255, 255, 0},
   .dns  = {8, 8, 8, 8},
   .dhcp = NETINFO_DHCP
};

步驟三：DHCP獲取網絡地址信息

首先是在初始化完硬件和TOE之后調用network_init進行網絡地址信息配置

network_init(ethernet_buf, &default_net_info);

這個函數需要將DHCP處理用到的緩存數組以及默認網絡地址信息傳入，函數具體內容如下：

/**
* @brief   set network information
*
* First determine whether to use DHCP. If DHCP is used, first obtain the Internet Protocol Address through DHCP.
* When DHCP fails, use static IP to configure network information. If static IP is used, configure network information directly
*
* @param   sn: socketid
* @param   ethernet_buff:
* @param   net_info: network information struct
* @return  none
*/
void network_init(uint8_t *ethernet_buff, wiz_NetInfo *conf_info)
{
   int ret;
   wizchip_setnetinfo(conf_info); // Configuring Network Information
   if (conf_info->dhcp == NETINFO_DHCP)
   {
       ret = wiz_dhcp_process(0, ethernet_buff);
       if (ret == 0)
       {
           conf_info->dhcp = NETINFO_STATIC;
           wizchip_setnetinfo(conf_info);
       }
   }
   print_network_information();
}

在這個函數中，會先設置一遍網絡地址到W55MH32中，然后判斷模式是否為DHCP模式，如果為DHCP模式，則使用wiz_dhcp_process函數來執行DHCP進程，在通過DHCP方式成功獲取到網絡地址后更新到W55MH32中，最后將網絡地址信息打印出來。wiz_dhcp_process函數內容如下：

/**
* @brief DHCP process
* @param sn :socket number
* @param buffer :socket buffer
*/
static uint8_t wiz_dhcp_process(uint8_t sn, uint8_t *buffer)
{
   wiz_NetInfo conf_info;
   uint8_t     dhcp_run_flag = 1;
   uint8_t     dhcp_ok_flag  = 0;
   /* Registration DHCP_time_handler to 1 second timer */
   DHCP_init(sn, buffer);
   printf("DHCP runningrn");
   while (1)
   {
       switch (DHCP_run())  // Do the DHCP client
       {
       case DHCP_IP_LEASED: // DHCP Acquiring network information successfully
           if (dhcp_ok_flag == 0)
           {
               dhcp_ok_flag  = 1;
               dhcp_run_flag = 0;
           }
           break;
       case DHCP_FAILED:
           dhcp_run_flag = 0;
           break;
       }
       if (dhcp_run_flag == 0)
       {
           printf("DHCP %s!rn", dhcp_ok_flag ? "success" : "fail");
           DHCP_stop();
           if (dhcp_ok_flag)
           {
               getIPfromDHCP(conf_info.ip);
               getGWfromDHCP(conf_info.gw);
               getSNfromDHCP(conf_info.sn);
               getDNSfromDHCP(conf_info.dns);
               conf_info.dhcp = NETINFO_DHCP;
               getSHAR(conf_info.mac);
               wizchip_setnetinfo(&conf_info); // Update network information to network information obtained by DHCP
               return 1;
           }
           return 0;
       }
   }
}

在該函數體中，首先會調用DHCP_init函數進行初始化DHCP配置：

void DHCP_init(uint8_t s, uint8_t * buf)
{
   uint8_t zeroip[4] = {0,0,0,0};
   getSHAR(DHCP_CHADDR);
   if((DHCP_CHADDR[0] | DHCP_CHADDR[1]  | DHCP_CHADDR[2] | DHCP_CHADDR[3] | DHCP_CHADDR[4] | DHCP_CHADDR[5]) == 0x00)
   {
     // assigning temporary mac address, you should be set SHAR before call this function. 
     DHCP_CHADDR[0] = 0x00;
     DHCP_CHADDR[1] = 0x08;
     DHCP_CHADDR[2] = 0xdc;      
     DHCP_CHADDR[3] = 0x00;
     DHCP_CHADDR[4] = 0x00;
     DHCP_CHADDR[5] = 0x00; 
     setSHAR(DHCP_CHADDR);     
   }
 DHCP_SOCKET = s; // SOCK_DHCP
 pDHCPMSG = (RIP_MSG*)buf;
 DHCP_XID = 0x12345678;
 {
   DHCP_XID += DHCP_CHADDR[3];
   DHCP_XID += DHCP_CHADDR[4];
   DHCP_XID += DHCP_CHADDR[5];
   DHCP_XID += (DHCP_CHADDR[3] ^ DHCP_CHADDR[4] ^ DHCP_CHADDR[5]);
 }
 // WIZchip Netinfo Clear
 setSIPR(zeroip);
 setGAR(zeroip);
 reset_DHCP_timeout();
 dhcp_state = STATE_DHCP_INIT;
}

然后是在DHCP主循環中運行DHCP_run函數，它的主要作用是進行DHCP組包，發送發現、請求等報文，對服務器的提供、響應等內容進行解析以及超時處理，這里只需要根據DHCP_run函數的返回值進行相應處理即可。DHCP_run函數內容如下：

uint8_t DHCP_run(void)
{
 uint8_t  type;
 uint8_t  ret;
 if(dhcp_state == STATE_DHCP_STOP) return DHCP_STOPPED;
 if(getSn_SR(DHCP_SOCKET) != SOCK_UDP)
     socket(DHCP_SOCKET, Sn_MR_UDP, DHCP_CLIENT_PORT, 0x00);
 ret = DHCP_RUNNING;
 type = parseDHCPMSG();
 switch ( dhcp_state ) {
     case STATE_DHCP_INIT     :
         DHCP_allocated_ip[0] = 0;
         DHCP_allocated_ip[1] = 0;
         DHCP_allocated_ip[2] = 0;
         DHCP_allocated_ip[3] = 0;
       send_DHCP_DISCOVER();
       dhcp_state = STATE_DHCP_DISCOVER;
       break;
   case STATE_DHCP_DISCOVER :
     if (type == DHCP_OFFER){
#ifdef _DHCP_DEBUG_
       printf("> Receive DHCP_OFFERrn");
#endif
           DHCP_allocated_ip[0] = pDHCPMSG->yiaddr[0];
           DHCP_allocated_ip[1] = pDHCPMSG->yiaddr[1];
           DHCP_allocated_ip[2] = pDHCPMSG->yiaddr[2];
           DHCP_allocated_ip[3] = pDHCPMSG->yiaddr[3];
       send_DHCP_REQUEST();
       dhcp_state = STATE_DHCP_REQUEST;
     } else ret = check_DHCP_timeout();
         break;
   case STATE_DHCP_REQUEST :
     if (type == DHCP_ACK) {
#ifdef _DHCP_DEBUG_
       printf("> Receive DHCP_ACKrn");
#endif
       if (check_DHCP_leasedIP()) {
         // Network info assignment from DHCP
         dhcp_ip_assign();
         reset_DHCP_timeout();
         dhcp_state = STATE_DHCP_LEASED;
       } else {
         // IP address conflict occurred
         reset_DHCP_timeout();
         dhcp_ip_conflict();
           dhcp_state = STATE_DHCP_INIT;
       }
     } else if (type == DHCP_NAK) {
#ifdef _DHCP_DEBUG_
       printf("> Receive DHCP_NACKrn");
#endif
       reset_DHCP_timeout();
       dhcp_state = STATE_DHCP_DISCOVER;
     } else ret = check_DHCP_timeout();
   break;
   case STATE_DHCP_LEASED :
       ret = DHCP_IP_LEASED;
     if ((dhcp_lease_time != INFINITE_LEASETIME) && ((dhcp_lease_time/2) < dhcp_tick_1s)) {
       
#ifdef _DHCP_DEBUG_
         printf("?> Maintains the IP address rn");
#endif
       type = 0;
       OLD_allocated_ip[0] = DHCP_allocated_ip[0];
       OLD_allocated_ip[1] = DHCP_allocated_ip[1];
       OLD_allocated_ip[2] = DHCP_allocated_ip[2];
       OLD_allocated_ip[3] = DHCP_allocated_ip[3];
       
       DHCP_XID++;
       send_DHCP_REQUEST();
       reset_DHCP_timeout();
       dhcp_state = STATE_DHCP_REREQUEST;
     }
   break;
   case STATE_DHCP_REREQUEST :
       ret = DHCP_IP_LEASED;
     if (type == DHCP_ACK) {
       dhcp_retry_count = 0;
       if (OLD_allocated_ip[0] != DHCP_allocated_ip[0] || 
           OLD_allocated_ip[1] != DHCP_allocated_ip[1] ||
           OLD_allocated_ip[2] != DHCP_allocated_ip[2] ||
           OLD_allocated_ip[3] != DHCP_allocated_ip[3]) 
       {
         ret = DHCP_IP_CHANGED;
         dhcp_ip_update();
               #ifdef _DHCP_DEBUG_
                 printf(">IP changed.rn");
               #endif
         
       }
         #ifdef _DHCP_DEBUG_
           else printf(">IP is continued.rn");
         #endif                
       reset_DHCP_timeout();
       dhcp_state = STATE_DHCP_LEASED;
     } else if (type == DHCP_NAK) {
#ifdef _DHCP_DEBUG_
       printf("> Receive DHCP_NACK, Failed to maintain iprn");
#endif
       reset_DHCP_timeout();
       dhcp_state = STATE_DHCP_DISCOVER;
     } else ret = check_DHCP_timeout();
       break;
   default :
       break;
 }
 return ret;
}

8運行結果

燒錄例程運行后，首先打印了PHY鏈路檢測的結果以及DHCP日志信息，然后打印了網絡地址信息，這里可以看到配置方式為DHCP，IP地址為192.168.1.117，最后是PING提示消息。

接著在PC端打開CMD，PING W55MH32的IP地址，可以正常PING通。

7總結

本文介紹 DHCP協議，包括其在 IP網絡自動分配參數的功能、便捷配置等特點、工作原理、報文格式和應用場景。通過 W55MH32實戰例程展示動態獲取網絡地址信息過程，含注冊定時器中斷、啟用模式和獲取信息等步驟，燒錄后可完成檢測與信息打印，PC端能 PING通設備。

下一篇文章將講解如何在 W55MH32芯片上實現 TCP客戶端模式，解析 TCP客戶端連接服務器進行回環測試的核心原理及應用，同時通過實戰例程講解具體實現步驟與要點，敬請期待！

WIZnet是一家無晶圓廠半導體公司，成立于 1998年。產品包括互聯網處理器 iMCU?，它采用 TOE（TCP/IP卸載引擎）技術，基于獨特的專利全硬連線 TCP/IP。iMCU?面向各種應用中的嵌入式互聯網設備。

WIZnet在全球擁有 70多家分銷商，在香港、韓國、美國設有辦事處，提供技術支持和產品營銷。

香港辦事處管理的區域包括：澳大利亞、印度、土耳其、亞洲（韓國和日本除外）。

審核編輯 黃宇