91 lines
3.2 KiB
C
91 lines
3.2 KiB
C
/*************************************************************************\
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* (C) 2014 David Lettier.
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* http://www.lettier.com/
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* SPDX-License-Identifier: BSD-3-Clause
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\*************************************************************************/
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#include <unistd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <errno.h>
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <netinet/in.h>
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#include <netdb.h>
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#include <arpa/inet.h>
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#include <rtems.h>
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#include "epicsNtp.h"
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int epicsNtpGetTime(char *ntpIp, struct timespec *now)
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{
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int sockfd, n; // Socket file descriptor and the n return result from writing/reading from the socket.
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int portno = 123; // NTP UDP port number.
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// Create and zero out the packet. All 48 bytes worth.
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ntp_packet packet = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
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memset( &packet, 0, sizeof( ntp_packet ) );
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// 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.
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*( ( char * ) &packet + 0 ) = 0x1b; // Represents 27 in base 10 or 00011011 in base 2.
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// Create a UDP socket, convert the host-name to an IP address, set the port number,
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// connect to the server, send the packet, and then read in the return packet.
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struct sockaddr_in serv_addr; // Server address data structure.
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sockfd = socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP ); // Create a UDP socket.
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if ( sockfd < 0 ) {
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perror( "epicsNtpGetTime creating socket" );
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return -1;
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}
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// Zero out the server address structure.
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memset( ( char* ) &serv_addr, 0, sizeof( serv_addr ) );
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serv_addr.sin_family = AF_INET;
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serv_addr.sin_addr.s_addr = inet_addr(ntpIp);
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serv_addr.sin_port = htons( portno );
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// Call up the server using its IP address and port number.
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if ( connect( sockfd, ( struct sockaddr * ) &serv_addr, sizeof( serv_addr) ) < 0 ) {
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perror( "epicsNtpGetTime connecting socket" );
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close( sockfd );
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return -1;
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}
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// Send it the NTP packet it wants. If n == -1, it failed.
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n = write( sockfd, ( char* ) &packet, sizeof( ntp_packet ) );
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if ( n < 0 ) {
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perror( "epicsNtpGetTime sending NTP request" );
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close( sockfd );
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return -1;
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}
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// Wait and receive the packet back from the server. If n == -1, it failed.
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n = read( sockfd, ( char* ) &packet, sizeof( ntp_packet ) );
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if ( n < 0 ) {
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perror( "epicsNtpGetTime reading NTP reply" );
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close( sockfd );
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return -1;
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}
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close( sockfd );
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// These two fields contain the time-stamp seconds as the packet left the NTP server.
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// The number of seconds correspond to the seconds passed since 1900.
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// ntohl() converts the bit/byte order from the network's to host's "endianness".
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packet.txTm_s = ntohl( packet.txTm_s ); // Time-stamp seconds.
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packet.txTm_f = ntohl( packet.txTm_f ); // Time-stamp fraction of a second.
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// Extract the 32 bits that represent the time-stamp seconds (since NTP epoch) from when the packet left the server.
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// Subtract 70 years worth of seconds from the seconds since 1900.
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// This leaves the seconds since the UNIX epoch of 1970.
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// (1900)------------------(1970)**************************************(Time Packet Left the Server)
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time_t txTm = ( time_t ) ( packet.txTm_s - NTP_TIMESTAMP_DELTA );
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now->tv_sec = txTm;
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return 0;
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}
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