The 4G module designed by the charging pile obtains NTP time through mqtt based on 4G network

/* ntpclient.c */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#include "stm32f10x.h"
#if 0
#define VERSION_3           3
#define VERSION_4           4

#define MODE_CLIENT         3
#define MODE_SERVER         4


#define NTP_LI              0
#define NTP_VN              VERSION_3   
#define NTP_MODE            MODE_CLIENT
#define NTP_STRATUM         0
#define NTP_POLL            4
#define NTP_PRECISION       -6

#define NTP_HLEN            48

#define NTP_PORT            123
#define NTP_SERVER          "182.92.12.11"

#define TIMEOUT             10

#define BUFSIZE             1500

#define JAN_1970            0x83aa7e80

#define NTP_CONV_FRAC32(x)  (uint64_t) ((x) * ((uint64_t)1<<32))    
#define NTP_REVE_FRAC32(x)  ((double) ((double) (x) / ((uint64_t)1<<32)))   

#define NTP_CONV_FRAC16(x)  (uint32_t) ((x) * ((uint32_t)1<<16))    
#define NTP_REVE_FRAC16(x)  ((double)((double) (x) / ((uint32_t)1<<16)))    


#define USEC2FRAC(x)        ((uint32_t) NTP_CONV_FRAC32( (x) / 1000000.0 )) 
#define FRAC2USEC(x)        ((uint32_t) NTP_REVE_FRAC32( (x) * 1000000.0 )) 


#define NTP_LFIXED2DOUBLE(x)    ((double) ( ntohl(((struct l_fixedpt *) (x))->intpart) - JAN_1970 + FRAC2USEC(ntohl(((struct l_fixedpt *) (x))->fracpart)) / 1000000.0 ))   


struct s_fixedpt {
    uint16_t    intpart;
    uint16_t    fracpart;
};

struct l_fixedpt {
    uint32_t    intpart;
    uint32_t    fracpart;
};

struct timeval {
time_t tv_sec;	// seconds 
long tv_usec;	// microseconds 
};

#define __BID_ENDIAN      0
#define __LITTLE_ENDIAN   1
#define __BYTE_ORDER   __LITTLE_ENDIAN

struct ntphdr {
#if __BYTE_ORDER == __BID_ENDIAN
    unsigned int    ntp_li:2;
    unsigned int    ntp_vn:3;
    unsigned int    ntp_mode:3;
#endif
#if __BYTE_ORDER == __LITTLE_ENDIAN
    unsigned int    ntp_mode:3;
    unsigned int    ntp_vn:3;
    unsigned int    ntp_li:2;
#endif
    uint8_t         ntp_stratum;
    uint8_t         ntp_poll;
    int8_t          ntp_precision;
    struct s_fixedpt    ntp_rtdelay;
    struct s_fixedpt    ntp_rtdispersion;
    uint32_t            ntp_refid;
    struct l_fixedpt    ntp_refts;
    struct l_fixedpt    ntp_orits;
    struct l_fixedpt    ntp_recvts;
    struct l_fixedpt    ntp_transts;
};



int get_ntp_packet(void *buf, size_t *size)
{
    struct ntphdr *ntp;
    struct timeval tv;


    if (!size || *size<NTP_HLEN)
        return -1;

    memset(buf, 0, *size);

    ntp = (struct ntphdr *) buf;
    ntp->ntp_li = NTP_LI;
    ntp->ntp_vn = NTP_VN;
    ntp->ntp_mode = NTP_MODE;
    ntp->ntp_stratum = NTP_STRATUM;
    ntp->ntp_poll = NTP_POLL;
    ntp->ntp_precision = NTP_PRECISION;

    gettimeofday(&tv, NULL);
    ntp->ntp_transts.intpart = htonl(tv.tv_sec + JAN_1970);
    ntp->ntp_transts.fracpart = htonl(USEC2FRAC(tv.tv_usec));

    *size = NTP_HLEN;

    return 0;
}


void print_ntp(struct ntphdr *ntp)
{
    time_t time;

    printf("LI:\t%d \n", ntp->ntp_li);
    printf("VN:\t%d \n", ntp->ntp_vn);
    printf("Mode:\t%d \n", ntp->ntp_mode);
    printf("Stratum:\t%d \n", ntp->ntp_stratum);
    printf("Poll:\t%d \n", ntp->ntp_poll);
    printf("precision:\t%d \n", ntp->ntp_precision);

    printf("Route delay:\t %lf \n",
    ntohs(ntp->ntp_rtdelay.intpart) + NTP_REVE_FRAC16(ntohs(ntp->ntp_rtdelay.fracpart)));
    printf("Route Dispersion:\t%lf \n",
    ntohs(ntp->ntp_rtdispersion.intpart) + NTP_REVE_FRAC16(ntohs(ntp->ntp_rtdispersion.fracpart)));
    printf("Referencd ID:\t %d \n", ntohl(ntp->ntp_refid));


    time = ntohl(ntp->ntp_refts.intpart) - JAN_1970;
    printf("Reference:\t%d %ld %s \n",
    ntohl(ntp->ntp_refts.intpart) - JAN_1970,
    FRAC2USEC(ntohl(ntp->ntp_refts.fracpart)),
    ctime(&time));

    time = ntohl(ntp->ntp_orits.intpart) - JAN_1970;
    printf("Originate:\t%d %d frac=%ld (%s) \n",
    ntohl(ntp->ntp_orits.intpart) - JAN_1970,
    FRAC2USEC(ntohl(ntp->ntp_orits.fracpart)),
    ntohl(ntp->ntp_orits.fracpart),
    ctime(&time) );

    time = ntohl(ntp->ntp_recvts.intpart) - JAN_1970;
    printf("Receive:\t%d %d (%s) \n",
    ntohl(ntp->ntp_recvts.intpart) - JAN_1970,
    FRAC2USEC(ntohl(ntp->ntp_recvts.fracpart)),
    ctime(&time) );

    time = ntohl(ntp->ntp_transts.intpart) - JAN_1970;
    printf("Transmit:\t%d %d (%s) \n",
    ntohl(ntp->ntp_transts.intpart) - JAN_1970,
    FRAC2USEC(ntohl(ntp->ntp_transts.fracpart)),
    ctime(&time) );
}


double get_rrt(const struct ntphdr *ntp, const struct timeval *recvtv)
{
    double t1, t2, t3, t4;

    t1 = NTP_LFIXED2DOUBLE(&ntp->ntp_orits);
    t2 = NTP_LFIXED2DOUBLE(&ntp->ntp_recvts);
    t3 = NTP_LFIXED2DOUBLE(&ntp->ntp_transts);
    t4 = recvtv->tv_sec + recvtv->tv_usec / 1000000.0;

    return (t4 - t1) - (t3 - t2);
}


double get_offset(const struct ntphdr *ntp, const struct timeval *recvtv)
{
    double t1, t2, t3, t4;

    t1 = NTP_LFIXED2DOUBLE(&ntp->ntp_orits);
    t2 = NTP_LFIXED2DOUBLE(&ntp->ntp_recvts);
    t3 = NTP_LFIXED2DOUBLE(&ntp->ntp_transts);
    t4 = recvtv->tv_sec + recvtv->tv_usec / 1000000.0;

    return ((t2 - t1) + (t3 - t4)) / 2;
}

#endif
#if 0
int main(int argc, char *argv[])
{
    char buf[BUFSIZE];
    size_t nbytes;
    struct timeval timeout, recvtv, tv;
    double offset;
	int i;
	int ret;

	ret = transport_open();
	if(ret){
		printf("open error!\n");
		return ret;
	}
	while(1){
    	nbytes = BUFSIZE;
    	if (get_ntp_packet(buf, &nbytes) != 0) {
    	    fprintf(stderr, "construct ntp request error \n");
    	    exit(-1);
   	 	}
		transport_sendPacketBuffer("\"182.92.12.11\",123",buf,nbytes);
		if((nbytes = transport_getdata(buf,BUFSIZE)) < 0){
			perror("recv error");
			exit(-1);
		}
		gettimeofday(&recvtv, NULL);
		offset = get_offset((struct ntphdr *)buf, &recvtv);

		gettimeofday(&tv, NULL);
		tv.tv_sec += (int) offset;
		tv.tv_usec += offset - (int) offset;
		printf("%s \n", ctime((time_t *) &tv.tv_sec));
	}

    return 0;
}
#endif