單芯片解決方案，開啟全新體驗(yàn)——W55MH32高性能以太網(wǎng)單片機(jī)

W55MH32是WIZnet重磅推出的高性能以太網(wǎng)單片機(jī)，它為用戶帶來(lái)前所未有的集成化體驗(yàn)。這顆芯片將強(qiáng)大的組件集于一身，具體來(lái)說，一顆W55MH32內(nèi)置高性能Arm? Cortex-M3核心，其主頻最高可達(dá)216MHz；配備1024KB FLASH與96KB SRAM，滿足存儲(chǔ)與數(shù)據(jù)處理需求；集成TOE引擎，包含WIZnet全硬件TCP/IP協(xié)議棧、內(nèi)置MAC以及PHY，擁有獨(dú)立的32KB以太網(wǎng)收發(fā)緩存，可供8個(gè)獨(dú)立硬件socket使用。如此配置，真正實(shí)現(xiàn)了All-in-One解決方案，為開發(fā)者提供極大便利。

在封裝規(guī)格上，W55MH32提供了兩種選擇：QFN100和QFN68。

W55MH32L采用QFN100封裝版本，尺寸為12x12mm，其資源豐富，專為各種復(fù)雜工控場(chǎng)景設(shè)計(jì)。它擁有66個(gè)GPIO、3個(gè)ADC、12通道DMA、17個(gè)定時(shí)器、2個(gè)I2C、5個(gè)串口、2個(gè)SPI接口（其中1個(gè)帶I2S接口復(fù)用）、1個(gè)CAN、1個(gè)USB2.0以及1個(gè)SDIO接口。如此豐富的外設(shè)資源，能夠輕松應(yīng)對(duì)工業(yè)控制中多樣化的連接需求，無(wú)論是與各類傳感器、執(zhí)行器的通信，還是對(duì)復(fù)雜工業(yè)協(xié)議的支持，都能游刃有余，成為復(fù)雜工控領(lǐng)域的理想選擇。同系列還有QFN68封裝的W55MH32Q版本，該版本體積更小，僅為8x8mm，成本低，適合集成度高的網(wǎng)關(guān)模組等場(chǎng)景，軟件使用方法一致。更多信息和資料請(qǐng)進(jìn)入http://www.w5500.com/網(wǎng)站或者私信獲取。

此外，本W(wǎng)55MH32支持硬件加密算法單元，WIZnet還推出TOE+SSL應(yīng)用，涵蓋TCP SSL、HTTP SSL以及 MQTT SSL等，為網(wǎng)絡(luò)通信安全再添保障。

為助力開發(fā)者快速上手與深入開發(fā)，基于W55MH32L這顆芯片，WIZnet精心打造了配套開發(fā)板。開發(fā)板集成WIZ-Link芯片，借助一根USB C口數(shù)據(jù)線，就能輕松實(shí)現(xiàn)調(diào)試、下載以及串口打印日志等功能。開發(fā)板將所有外設(shè)全部引出，拓展功能也大幅提升，便于開發(fā)者全面評(píng)估芯片性能。

若您想獲取芯片和開發(fā)板的更多詳細(xì)信息，包括產(chǎn)品特性、技術(shù)參數(shù)以及價(jià)格等，歡迎訪問官方網(wǎng)頁(yè)：http://www.w5500.com/，我們期待與您共同探索W55MH32的無(wú)限可能。

第二章 W55MH32 DHCP示例

本篇文章我們將詳細(xì)講解DHCP協(xié)議的基本信息、優(yōu)勢(shì)特點(diǎn)、工作原理、應(yīng)用場(chǎng)景，并通過實(shí)戰(zhàn)例程，為大家講解如何使用W55MH32動(dòng)態(tài)獲取IP信息，幫助讀者更好地了解并運(yùn)用這一協(xié)議。

有關(guān)W55MH32的初始化過程，請(qǐng)參考相關(guān)章節(jié)，這里將不再詳述。

1 DHCP協(xié)議簡(jiǎn)介

DHCP（Dynamic Host Configuration Protocol）即動(dòng)態(tài)主機(jī)配置協(xié)議，是一個(gè)應(yīng)用層協(xié)議。它主要用于在 IP網(wǎng)絡(luò)中為客戶端自動(dòng)分配 IP地址及其他相關(guān)網(wǎng)絡(luò)配置參數(shù)，如子網(wǎng)掩碼、默認(rèn)網(wǎng)關(guān)、DNS服務(wù)器地址等。這種動(dòng)態(tài)分配的方式大大簡(jiǎn)化了網(wǎng)絡(luò)管理員的工作，并且能夠更有效地利用有限的 IP地址資源。

2 DHCP協(xié)議特點(diǎn)

便捷配置與管控：DHCP可自動(dòng)分配IP地址、子網(wǎng)掩碼、網(wǎng)關(guān)、DNS等網(wǎng)絡(luò)參數(shù)，設(shè)備入網(wǎng)即自動(dòng)獲取，用戶無(wú)需手動(dòng)操作。管理員能通過服務(wù)器集中管理IP分配，網(wǎng)絡(luò)架構(gòu)調(diào)整時(shí)，修改服務(wù)器設(shè)置，客戶端自動(dòng)適配；靜態(tài)IP則要逐臺(tái)手動(dòng)輸入、調(diào)整，流程繁瑣還易出錯(cuò)。

靈活資源利用：DHCP動(dòng)態(tài)分配IP，設(shè)備離線后地址回池再利用，契合公共場(chǎng)所臨時(shí)大量接入需求，提升地址利用率；還能按需靈活調(diào)配，為關(guān)鍵設(shè)備保留靜態(tài)IP，其余動(dòng)態(tài)分配。靜態(tài)IP固定占用，閑置浪費(fèi)資源，靈活性差。

高效維護(hù)與排障：DHCP自動(dòng)分配，規(guī)避手動(dòng)配置錯(cuò)誤與IP地址沖突，服務(wù)器詳細(xì)記錄分配情況。網(wǎng)絡(luò)故障時(shí)，管理員依服務(wù)器日志鎖定故障設(shè)備排查；靜態(tài)IP手動(dòng)配置易沖突，故障排查缺少有效記錄，難度大、耗時(shí)久。

適配移動(dòng)與拓展：移動(dòng)設(shè)備橫跨網(wǎng)絡(luò)時(shí)，DHCP讓其自動(dòng)獲取IP配置，無(wú)需手動(dòng)切換；網(wǎng)絡(luò)規(guī)模擴(kuò)大、新增設(shè)備時(shí)，DHCP自動(dòng)分配地址，助力快速擴(kuò)容。靜態(tài)IP需提前規(guī)劃，易現(xiàn)地址不足、分配不合理問題，還增加設(shè)備移動(dòng)操作難度。

3 DHCP工作原理

DHCP工作原理如圖所示：

從圖示中我們可以直觀明了地看出DHCP地工作原理，一般為四個(gè)階段：

發(fā)現(xiàn)階段：客戶端接入網(wǎng)絡(luò)時(shí)以廣播形式發(fā)送DHCP Discover報(bào)文（目的IP是255.255.255.255，源IP是0.0.0.0）尋找DHCP服務(wù)器，報(bào)文中含客戶端MAC地址。若服務(wù)器和客戶端不在同一子網(wǎng)，會(huì)通過中繼代理（如路由器）轉(zhuǎn)發(fā)。

提供階段：DHCP服務(wù)器收到Discover報(bào)文后，從IP地址池選一個(gè)未分配的IP地址，將其和子網(wǎng)掩碼、默認(rèn)網(wǎng)關(guān)、DNS服務(wù)器地址等信息封裝進(jìn)DHCP Offer報(bào)文，以廣播或單播方式發(fā)給客戶端，可能會(huì)有多個(gè)Offer報(bào)文。

請(qǐng)求階段：客戶端收到多個(gè)Offer后選擇一個(gè)，以廣播形式發(fā)送DHCP Request報(bào)文請(qǐng)求分配該IP地址等配置信息，且發(fā)送ARP請(qǐng)求檢查IP地址唯一性。

確認(rèn)階段：服務(wù)器收到Request報(bào)文后，檢查IP地址是否可用。若可用，將以廣播或單播的形式發(fā)送DHCP Ack報(bào)文，客戶端收到后完成網(wǎng)絡(luò)配置正常上網(wǎng)。若不可用，發(fā)送DHCP Nak報(bào)文，客戶端收到后重新發(fā)起Discover流程。

4 DHCP協(xié)議報(bào)文

DHCP的報(bào)文格式如下：

DHCP報(bào)文各字段的說明如下表所示：

Discover報(bào)文實(shí)例：客戶端通過UDP廣播的方式發(fā)送DHCP發(fā)現(xiàn)報(bào)文，報(bào)文中包含了客戶端MAC地址、主機(jī)名和請(qǐng)求的IP地址等信息

|報(bào)文解析|
Message type: Boot Request (1)（op code為1，客戶端請(qǐng)求報(bào)文）
Hardware type: Ethernet (0x01)
Hardware address length: 6
Hops: 0
Transaction ID: 0xbf600589
Seconds elapsed: 0
Bootp flags: 0x0000 (Unicast)
Client IP address: 0.0.0.0
Your (client) IP address: 0.0.0.0
Next server IP address: 0.0.0.0
Relay agent IP address: 0.0.0.0
Client MAC address: HP_b1:37:11 (64:4e:d7:b1:37:11)
Client hardware address padding: 00000000000000000000
Server host name not given
Boot file name not given
Magic cookie: DHCP
Option: (53) DHCP Message Type (Discover)
Option: (61) Client identifier
Option: (50) Requested IP Address (192.168.1.115)
Option: (12) Host Name
Option: (60) Vendor class identifier
Option: (55) Parameter Request List
Option: (255) End
Padding: 0000000000000000

|報(bào)文原文|
01 01 06 00 bf 60
05 89 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 64 4e d7 b1 37 11 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 63 82 53 63 35 01 01 3d 07 01 64 4e d7 b1 37 11 32 04 c0 a8 01 73 0c 05 46 41 45 5f 33 3c 08 4d 53 46 54 20 35 2e 30 37 0e 01 03 06 0f 1f 21 2b 2c 2e 2f 77 79 f9 fc ff 00 00 00 00 00 00 00 00

Offer報(bào)文實(shí)例：DHCP服務(wù)器收到Discover報(bào)文后，從IP地址池選一個(gè)未分配的IP地址，將其和子網(wǎng)掩碼、默認(rèn)網(wǎng)關(guān)等信息封裝進(jìn)Offer報(bào)文以廣播或單播（這里為廣播的方式）方式發(fā)給客戶端

|報(bào)文解析|
Message type: Boot Reply (2)（op code為2，服務(wù)器響應(yīng)報(bào)文）
Hardware type: Ethernet (0x01)
Hardware address length: 6
Hops: 0
Transaction ID: 0xbf600589
Seconds elapsed: 0
Bootp flags: 0x0000 (Unicast)
Client IP address: 0.0.0.0
Your (client) IP address: 192.168.1.115
Next server IP address: 0.0.0.0
Relay agent IP address: 0.0.0.0
Client MAC address: HP_b1:37:11 (64:4e:d7:b1:37:11)
Client hardware address padding: 00000000000000000000
Server host name not given
 Boot file name not given
Magic cookie: DHCP
Option: (53) DHCP Message Type (Offer)
Option: (54) DHCP Server Identifier (192.168.1.1)
 Option: (51) IP Address Lease Time
 Option: (6) Domain Name Server
Option: (1) Subnet Mask (255.255.255.0)
Option: (3) Router
Option: (255) End
|報(bào)文原文|
02 01 06 00 bf 60
05 89 00 00 00 00 00 00 00 00 c0 a8 01 73 00 00 00 00 00 00 00 00 64 4e d7 b1 37 11 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 63 82 53 63 35 01 02 36 04 c0 a8 01 01 33 04 00 00 1c 20 06 08 ca 60 86 21 ca 60 80 56 01 04 ff ff ff 00 03 04 c0 a8 01 01 ff

其他報(bào)文信息這里就不一一展示了，感興趣的朋友可以自行抓取查看。

5 DHCP應(yīng)用場(chǎng)景

DHCP的應(yīng)用場(chǎng)景通常集中在需要?jiǎng)討B(tài)分配IP地址的局域網(wǎng)環(huán)境中。例如，在大型的辦公環(huán)境或者學(xué)校中，由于有大量的網(wǎng)絡(luò)設(shè)備需要連接到網(wǎng)絡(luò)，手動(dòng)為每個(gè)設(shè)備分配和管理IP地址會(huì)非常繁瑣且容易出錯(cuò)。使用DHCP可以集中管理IP地址的分配，提高網(wǎng)絡(luò)管理員的工作效率，減少錯(cuò)誤的發(fā)生，且可以適應(yīng)網(wǎng)絡(luò)變化。

6實(shí)現(xiàn)過程

接下來(lái)，我們一起來(lái)看看如何在W55MH32上實(shí)現(xiàn)DHCP動(dòng)態(tài)獲取網(wǎng)絡(luò)地址信息。

注意：使用DHCP動(dòng)態(tài)獲取IP時(shí)，必需將網(wǎng)絡(luò)結(jié)構(gòu)體配置中dhcp的值改為NETINFO_DHCP，這樣才能運(yùn)行DHCP模式。

步驟一：注冊(cè)DHCP定時(shí)器中斷到1s定時(shí)器中：

/**
* @brief   1ms timer IRQ Handler
* @param   none
* @return  none
*/
void TIM3_IRQHandler(void)
{
   static uint32_t tim3_1ms_count = 0;
   if (TIM_GetITStatus(TIM3, TIM_IT_Update) != RESET)
   {
       tim3_1ms_count++;
       if (tim3_1ms_count >= 1000)
       {
           DHCP_time_handler();
           tim3_1ms_count = 0;
       }
       TIM_ClearITPendingBit(TIM3, TIM_IT_Update);
   }
}

注冊(cè)DHCP定時(shí)器中斷主要為了DHCP超時(shí)處理。

在dhcp.h文件中，定義了DHCP超時(shí)時(shí)間、重試次數(shù)、端口號(hào)和主機(jī)名等內(nèi)容：

/* Retry to processing DHCP */
#define MAX_DHCP_RETRY          2        ///< Maximum retry count
#define DHCP_WAIT_TIME          10       ///< Wait Time 10s

/* UDP port numbers for DHCP */
#define DHCP_SERVER_PORT       67       ///< DHCP server port number
#define DHCP_CLIENT_PORT         68       ///< DHCP client port number

#define MAGIC_COOKIE             0x63825363  ///< You should not modify it number.
#define DCHP_HOST_NAME           "WIZnet"

步驟二：?jiǎn)⒂肈HCP動(dòng)態(tài)獲?。?/strong>

/* 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
};

network_init(ethernet_buf, &default_net_info);

/**
* @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();
}

/**
* @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;
       }
   }
}

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;
}

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;
}