RDS Group 4 CT(time) generation script

rds_ct_gen.c

#include <stdint.h>
#include <stdio.h>
#include <time.h>
#include <stdlib.h>

uint16_t blocks[3];

void main(){
        // Check time
        time_t now;
        struct tm *utc;

        now = time(NULL);
        utc = gmtime (&now);

        // Generate CT group
        int l = utc->tm_mon <= 1 ? 1 : 0;
        int mjd = 14956 + utc->tm_mday +
                                        (int)((utc->tm_year - l) * 365.25) +
                                        (int)((utc->tm_mon + 2 + l*12) * 30.6001);

        // 0x4400 means TP(Traffic Program) bit is set to on
        // If you don't want this, change to 0x4000
        // PTY can also be calculated, but it's irrelevant in group 4 data
        blocks[0] = 0x4400 | (mjd>>15);
        blocks[1] = (mjd<<1) | (utc->tm_hour>>4);
        blocks[2] = (utc->tm_hour & 0xF)<<12 | utc->tm_min<<6;

        utc = localtime(&now);

        //Beware that RDS timezone offset is calculated per half an hour
        int offset = utc->tm_gmtoff / (30 * 60);
        blocks[2] |= abs(offset);
        if(offset < 0) blocks[2] |= 0x20;

        printf("Generated CT: %04X %04X %04X\n", blocks[0], blocks[1], blocks[2]);
}