NTP 实现 C

Question

有人能找到我在 ntp 实施中遗漏的内容吗？

我正在为 32 位微控制器 ARM Cortex M3 编程。我有三个函数 - wifiSend，它调用 bsdUdpClient 和 bsdUdpServer。 bsdUdpClient向服务器发送数据，bsdUdpServer监听保留的NTP端口，接收NTP服务器的数据。

我没有收到任何错误消息，但收到的缓冲区是空的。

    static void wifiSend(xTimerHandle xTimer){

         uint16_t AddrSize = sizeof(SlSockAddrIn_t);

         if (STATUS_OK != bsdUdpClient(SERVER_PORT, AddrSize)){
               printf("Failed to send udp packet\n\r");
               assert(false);
         }

         if (STATUS_OK != bsdUdpServer(SERVER_PORT, AddrSize))
            printf("Failed to receive udp packet\n\r");
    }


    static returnTypes_t bsdUdpClient(uint16_t port, uint16_t AddrSize){

          int16_t Status = (int16_t) ZERO;

          memset(packetBuffer, 0, NTP_PACKET_SIZE);

          packetBuffer[0] = 0xE3; //0b11100011;   // LI, Version, Mode
          packetBuffer[1] = 0x00;     // Stratum, or type of clock
          packetBuffer[2] = 0x06;     // Polling Interval
          packetBuffer[3] = 0xEC;  // Peer Clock Precision
          // 8 bytes of zero for Root Delay & Root Dispersion
          packetBuffer[12]  = 49;
          packetBuffer[13]  = 0x4E;
          packetBuffer[14]  = 49;
          packetBuffer[15]  = 52;
          Addr.sin_family = SL_AF_INET;
          Addr.sin_port = sl_Htons((uint16_t) port);
          Addr.sin_addr.s_addr = sl_Htonl(SERVER_IP);

          SockID = sl_Socket(SL_AF_INET, SL_SOCK_DGRAM, (uint32_t) ZERO);
          if (SockID < (int16_t) ZERO)
               return (SOCKET_ERROR);

          Status = sl_SendTo(SockID, packetBuffer, NTP_PACKET_SIZE *     sizeof(uint8_t), (uint32_t) ZERO, (SlSockAddr_t *) &Addr, AddrSize);


          if (Status <= (int16_t) ZERO) {
              Status = sl_Close(SockID);
              if (Status < 0)
                     return (SEND_ERROR);
              return (SEND_ERROR);
          }

          Status = sl_Close(SockID);
          if (Status < 0)
               return (SEND_ERROR);

          return (STATUS_OK);
    }

    static returnTypes_t bsdUdpServer(uint16_t port, uint16_t AddrSize){

          int16_t Status = (int16_t) ZERO;

          LocalAddr.sin_family = SL_AF_INET;
          LocalAddr.sin_port = sl_Htons(5001);
          LocalAddr.sin_addr.s_addr = 0;

          SockID = sl_Socket(SL_AF_INET,SL_SOCK_STREAM, (uint32_t) ZERO);
          if (SockID < 0){
               printf("error on sl_Socket\n\r");
               return SOCKET_ERROR;
          }

          Status = sl_Bind(SockID, (SlSockAddr_t *) &LocalAddr, AddrSize);
          if (Status < 0){
               printf("problem on sl_Bind\n\r");
               return SOCKET_ERROR;
          }

          Status = sl_RecvFrom(SockID, packetBuffer, NTP_PACKET_SIZE * sizeof(uint8_t), (uint32_t) ZERO, (SlSockAddr_t *) &Addr, &AddrSize);
          if (Status < (int16_t) ZERO){
               printf("error - no bytes received: %d\n\r", (int16_t)Status);
               return SOCKET_ERROR;
          }

          Status = sl_Close(SockID);
          if (Status < 0)
               printf("problem on sl_Close\n\r");

          uint8_t index3 = packetBuffer[40];
          uint8_t index2 = packetBuffer[41];
          uint8_t index1 = packetBuffer[42];
          uint8_t index0 = packetBuffer[43];

          uint16_t highWord = index3 << 16 | index2;
          uint16_t lowWord = index1 << 16 | index0;

          uint32_t secondsSince1900 = highWord << 16 | lowWord;

          printf("Seconds since 1 Janeiro de 1900: %ld\n\r", secondsSince1900);

          return (STATUS_OK);

 }

Answer 1

您的客户端代码发送了一个查询，但随后关闭了套接字并且从不监听回复。

您的服务器代码等待查询，但从不发送任何响应。

它们似乎都没有做任何特别有用的事情。您应该完成客户端代码，以便它在关闭套接字之前侦听回复。请注意，您应该使用超时，这样您就不会在查询或响应丢失的情况下永远等待。

Answer 2

感谢@DavidSchwartz，我现在有了一个可行的解决方案。

我还修复了一个错误，当时我试图从收到的数据包中提取自 1900 年 1 月 1 日以来的秒数。

希望对大家有所帮助。

待改进：添加超时以避免服务器无响应时的阻塞状态

#define NTP_PACKET_SIZE         48
uint8_t packetBuffer[ NTP_PACKET_SIZE];

static returnTypes_t bsdUdpClient(uint16_t AddrSize){

    int16_t Status = (int16_t) ZERO;

    memset(packetBuffer, 0, NTP_PACKET_SIZE);

    // Initialize values needed to form NTP request
    packetBuffer[0] = 0xE3; //0b11100011;   // LI, Version, Mode
    packetBuffer[1] = 0x00;     // Stratum, or type of clock
    packetBuffer[2] = 0x06;     // Polling Interval
    packetBuffer[3] = 0xEC;  // Peer Clock Precision
    // 8 bytes of zero for Root Delay & Root Dispersion
    packetBuffer[12]  = 49;
    packetBuffer[13]  = 0x4E;
    packetBuffer[14]  = 49;
    packetBuffer[15]  = 52;

    SockID = sl_Socket(SL_AF_INET, SL_SOCK_DGRAM, (uint32_t) ZERO);
    if (SockID < (int16_t) ZERO)
        return (SOCKET_ERROR);

    /*make the request to the server*/
    Status = sl_SendTo(SockID, packetBuffer, NTP_PACKET_SIZE * sizeof(uint8_t), (uint32_t) ZERO, (SlSockAddr_t *) &Addr, AddrSize);

    /*Check if 0 transmitted bytes sent or error condition*/
    if (Status <= (int16_t) ZERO) {
        sl_Close(SockID);
        return (SEND_ERROR);
    }
    else
        printf("request sent successfully\n\r");

    /* receive the reply from the server*/
    Status = sl_RecvFrom(SockID, packetBuffer, NTP_PACKET_SIZE * sizeof(uint8_t), (uint32_t) ZERO, (SlSockAddr_t *) &Addr, &AddrSize);
    if (Status < (int16_t) ZERO){
        printf("error - no bytes received: %d\n\r", (int16_t)Status);
        return SOCKET_ERROR;
    }
    else
        printf("reply received\n\r");

    Status = sl_Close(SockID);
    if (Status < 0)
        printf("problem on sl_Close\n\r");

    uint8_t index3 = packetBuffer[40];
    uint8_t index2 = packetBuffer[41];
    uint8_t index1 = packetBuffer[42];
    uint8_t index0 = packetBuffer[43];

    uint16_t highWord = index3 << 8 | index2;
    uint16_t lowWord = index1 << 8 | index0;

    uint32_t secondsSince1900 = highWord << 16 | lowWord;

    printf("Seconds since 1 Janeiro de 1900: %lu\n\r", secondsSince1900);

    return (STATUS_OK);

}

NTP 实现 C

NTP implementation C

c

microcontroller

ntp