目标：STM32端作为客户端，然后发送ping命令，检查客户端到服务端的网络通断问题。

内容实质：客服端发送ICMP数据包，等待服务端的响应。有响应：网络正常，无响应：网络断开。

参考资料：1、《嵌入式网络那些事》--五木  2、http://blog.csdn.net/jtttl/article/details/50583462

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关键代码：

/** ping identifier - must fit on a u16_t */

#ifndef PING_ID

#define PING_ID        0xAFAF

#endif

/** ping additional data size to include in the packet */

#ifndef PING_DATA_SIZE

#define PING_DATA_SIZE 32

#endif

/* ping variables */

static u16_t ping_seq_num;

static struct raw_pcb *ping_pcb = NULL;

static ip_addr_t ping_dst;

//组装报文

static void ping_prepare_echo( struct icmp_echo_hdr *iecho, u16_t len)

{

size_t i;

size_t data_len = len - sizeof(struct icmp_echo_hdr);

ICMPH_TYPE_SET(iecho, ICMP_ECHO);

ICMPH_CODE_SET(iecho, 0);

iecho->chksum = 0;

iecho->id    = PING_ID;

iecho->seqno  = htons(++ping_seq_num);

/* fill the additional data buffer with some data */

for(i = 0; i < data_len; i++) {

((char*)iecho)[sizeof(struct icmp_echo_hdr) + i] = (char)i;

}

iecho->chksum = inet_chksum(iecho, len);

}

static void ping_send(struct raw_pcb *raw, ip_addr_t *addr)

{

struct pbuf *p;

struct icmp_echo_hdr *iecho;

size_t ping_size = sizeof(struct icmp_echo_hdr) + PING_DATA_SIZE;

LWIP_ASSERT("ping_size <= 0xffff", ping_size <= 0xffff);

p = pbuf_alloc(PBUF_IP, (u16_t)ping_size, PBUF_RAM);

if (!p) {

return;

}

if ((p->len == p->tot_len) && (p->next == NULL)) {

iecho = (struct icmp_echo_hdr *)p->payload;

ping_prepare_echo(iecho, (u16_t)ping_size);

//发送

raw_sendto(raw, p, addr);

}

pbuf_free(p);

}

//发送ping包

void pingCmdSend(void)

{

ping_send(ping_pcb, &ping_dst);

}

//初始化

void ping_init(void)

{

     ping_pcb = raw_new(IP_PROTO_ICMP);

     IP4_ADDR(&ping_dst, 192,168,1,100);//服务端地址

}

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//freertos 任务

void  tcpClient(void *arg)

{

/* init code for LWIP */

MX_LWIP_Init();

//ping命令初始化

ping_init();

for(;;){

         pingCmdSend();

         vTaskDelay(5000);//每5sping一次服务端

}

}