ntp 校时 linux 带源码

大家好，又见面了，我是你们的朋友全栈君。

最近做个项目，想通过公网上的NTP服务器给板子校时，但是板子里没有ntpdate这个命令， 

下面是2个解决方法，

1，找到ntpdate源代码，重新编译之后，手动运行，

这个方法我上网上查了，比较复杂，据说NTP还与SSL有关，编译的时候必须把SSL也包含进去，于是就迟迟没有动工。

2，突然有一天看到rtthread里也提供一个ntp的客户端，比较简单，就一个文件，也没几行，于是想着把这个.c文件移植到linux下，但我仔细研究了一下，发现这个文件的原始作者就是在linux下设计的。原始文件更简单，就几行代码

就是下面的代码，很简单，于是果断移植这个程序，顺利的实现了校时。其实ntp协议也很简单。关键是这个结构体

int main( void )
{

  int sockfd, n; // Socket file descriptor and the n return result from writing/reading from the socket.

  int portno = 123; // NTP UDP port number.

  //char* host_name = “us.pool.ntp.org”; // NTP server host-name.
    char* host_name = “cn.ntp.org.cn”; // NTP server host-name.

  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: 384 bits or 48 bytes.

  // Create and zero out the packet. All 48 bytes worth.

  ntp_packet packet = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };

  memset( &packet, 0, sizeof( ntp_packet ) );

  // Set the first byte’s bits to 00,011,011 for li = 0, vn = 3, and mode = 3. The rest will be left set to zero.

  *( ( char * ) &packet + 0 ) = 0x1b; // Represents 27 in base 10 or 00011011 in base 2.

  struct sockaddr_in serv_addr; // Server address data structure.
  struct hostent *server;      // Server data structure.

  sockfd = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP ); // Create a UDP socket.

  if ( sockfd < 0 )
    error( “ERROR opening socket” );

  server = gethostbyname( host_name ); // Convert URL to IP.

  if ( server == NULL )
    error( “ERROR, no such host” );

  // Zero out the server address structure.

  bzero( ( char* ) &serv_addr, sizeof( serv_addr ) );

  serv_addr.sin_family = AF_INET;

  // Copy the server’s IP address to the server address structure.

  bcopy( ( char* )server->h_addr, ( char* ) &serv_addr.sin_addr.s_addr, server->h_length );

  serv_addr.sin_port = htons( portno );

  // Call up the server using its IP address and port number.

  if ( connect( sockfd, ( struct sockaddr * ) &serv_addr, sizeof( serv_addr) ) < 0 )
    error( “ERROR connecting” );

  n = write( sockfd, ( char* ) &packet, sizeof( ntp_packet ) );

  if ( n < 0 )
    error( “ERROR writing to socket” );

  // Wait and receive the packet back from the server. If n == -1, it failed.

  n = read( sockfd, ( char* ) &packet, sizeof( ntp_packet ) );

  if ( n < 0 )
    error( “ERROR reading from socket” );

  packet.txTm_s = ntohl( packet.txTm_s ); // Time-stamp seconds.
  packet.txTm_f = ntohl( packet.txTm_f ); // Time-stamp fraction of a second.

  time_t txTm = ( time_t ) ( packet.txTm_s – NTP_TIMESTAMP_DELTA );

  // Print the time we got from the server, accounting for local timezone and conversion from UTC time.

  txTm = txTm + 8*60*60;    //willow add
  printf( “Time: %s”, ctime( ( const time_t* ) &txTm ) );
  
  set_time_t(txTm);    //willow add 200924

  LOG_F(“set time from NTP:%s\r”, ctime(&(txTm)));

  return 0;
}