ntp协议详解_ntp端口号能否被修改

 //宏定义
#define NTP_TIMESTAMP_DELTA 2208988800ull //number of seconds between 1900 and 1970，1900-1970的时间差
#define SEC_TIME_ZONE + (8*60*60) //Beijing,GMT+8， 时区差


typedef struct
{

    uint8_t li_vn_mode;      // Eight bits. li, vn, and mode.
                             // li. Two bits. Leap indicator.
                            // vn. Three bits. Version number of the protocol.
                            // mode. Three bits. Client will pick mode 3 for client.

    uint8_t stratum;         // Eight bits. Stratum level of the local clock.
    uint8_t poll;            // Eight bits. Maximum interval between successive messages.
    uint8_t precision;       // Eight bits. Precision of the local clock.

    uint32_t rootDelay;      // 32 bits. Total round trip delay time.
    uint32_t rootDispersion; // 32 bits. Max error aloud from primary clock source.
    uint32_t refId;          // 32 bits. Reference clock identifier.

    uint32_t refTm_s;        // 32 bits. Reference time-stamp seconds.
    uint32_t refTm_f;        // 32 bits. Reference time-stamp fraction of a second.

    uint32_t origTm_s;       // 32 bits. Originate time-stamp seconds.
    uint32_t origTm_f;       // 32 bits. Originate time-stamp fraction of a second.

    uint32_t rxTm_s;         // 32 bits. Received time-stamp seconds.
    uint32_t rxTm_f;         // 32 bits. Received time-stamp fraction of a second.

    uint32_t txTm_s;         // 32 bits and the most important field the client cares about. Transmit time-stamp seconds.
    uint32_t txTm_f;         // 32 bits. Transmit time-stamp fraction of a second.

} ntp_packet;              // Total: 48 bytes.

void NTP_Func(void)
{
uint8_t addr[4]={
192,168,4,9};//本地模拟开启的一个服务器
uint8_t i;
uint8_t buf[48];
uint16_t port=0;
uint16_t *Pport=&port;
uint32_t local_timestamp; 
ntp_packet packet ;
struct tm * Net_time; 
uint8_t NTP_Data[48]; //48字节的报文
NTP_Data[0]=0xa3; 
//00100011, 0xa3,100 版本4
//00011011, 0x1b,011 版本3
//00010011, 0x13,010 版本2
//00001011, 0x0b,001 版本1
//后面分别发送了4个不同版本，都可以收到数据。
for(i=1;i<48;i++)NTP_Data[i]=0;//剩余的47字节为0
socket(3,Sn_MR_UDP,8080,0x00);//本地打开一个socket3,协议是UDP协议，端口是8080
sendto(3,NTP_Data,48,addr,123);//向addr的123端口发送报文，NTP使用的是UDP和123端口。
recvfrom(3,buf,48,addr,Pport);//接收返回的数据,48字节
//其中，sendto和recvfrom是w5500网口芯片自带的socket.c中的函数
//注意：UDP模式发送和接收使用sendto和recvfrom函数，TCP模式使用send和recv函数，当时调试时不知道，使用send和recv函数一直无法收到数据，卡了好久。
packet.txTm_s = buf[40]<<24 | buf[40+1]<<16|buf[40+2]<<8 |buf[40+3];//由于本文的时间精度要求不高，故自己用服务器返回的时间作为对时的时间，并未用公式：时间差offset=（（T2-T1）+（T3-T4））/2。而是用T3作为对时基准时间。 
local_timestamp = packet.txTm_s - NTP_TIMESTAMP_DELTA;//减去1970和1900的差值
local_timestamp +=SEC_TIME_ZONE; //加上北京的时间差，GMT+8
Net_time = localtime(&local_timestamp); //秒数转换位标准时间，下一篇将详细讲解Time.h中的时间转换函数 
printf("%d-%d-%d %d:%d:%d\r\n",(Net_time->tm_year)+1900, (Net_time->tm_mon)+1, Net_time->tm_mday, Net_time->tm_hour,Net_time->tm_min,Net_time->tm_sec); //打印出时间
}