// 2012-05-15 David Goncalves
//            Simple function to get time from an NTP server
//
//            This code is provided as is for testing purpose.
//            You can use it for free at your own risks.

unsigned long GetTimeFromNTPServer( byte *address, byte timeout )
{
    static EthernetUDP udp_handler;
    
    // Create a 48 byte buffer and clear it as NTP data is 48 bytes long
    byte PacketBuffer[ 48 ];
    memset( PacketBuffer, 0, 48 );
    
    PacketBuffer[0]  = 0b11100011; //  [11] Leap Indicator
                                   // [100] NTP Version 4
                                   // [011] Mode 3 -> NTP Client
    PacketBuffer[1]  = 0;
    PacketBuffer[2]  = 6;
    PacketBuffer[3]  = 0xEC;
    
    udp_handler.begin( 9999 );
    udp_handler.beginPacket( address, 123 );
    udp_handler.write( PacketBuffer, 48 );
    udp_handler.endPacket();
    
    unsigned long time_sent = millis();
    unsigned long secs      = 0;
    
    while ( millis() < ( ( timeout * 1000 ) + time_sent ) )
    {
        if ( udp_handler.parsePacket() )
        {
            udp_handler.read( PacketBuffer, 48 );
            
            // We only get the 32 bits containing the seconds ( bytes 40 -> 43 ) as we
            // do not need microseconds precision.
            // NTP protocol gives time in seconds since 1900.01.01 so 2208988800s earlier
            // than unix time which is from 1970.01.01.
            unsigned long msb  = word( PacketBuffer[40], PacketBuffer[41] );
            unsigned long lsb  = word( PacketBuffer[42], PacketBuffer[43] );
            secs               = msb << 16 | lsb;
            secs              -= 2208988800UL;
            break;
        }
        delay( 200 ); // wait 200ms before each try
    }
    
    return( secs );
}