unleashed-firmware/applications/plugins/gps_nmea_uart/minmea.c

/*
 * Copyright © 2014 Kosma Moczek <kosma@cloudyourcar.com>
 * This program is free software. It comes without any warranty, to the extent
 * permitted by applicable law. You can redistribute it and/or modify it under
 * the terms of the Do What The Fuck You Want To Public License, Version 2, as
 * published by Sam Hocevar. See the COPYING file for more details.
 */

#include "minmea.h"

#include <stdlib.h>
#include <string.h>
#include <stdarg.h>

#define boolstr(s) ((s) ? "true" : "false")

static int hex2int(char c) {
    if(c >= '0' && c <= '9') return c - '0';
    if(c >= 'A' && c <= 'F') return c - 'A' + 10;
    if(c >= 'a' && c <= 'f') return c - 'a' + 10;
    return -1;
}

uint8_t minmea_checksum(const char* sentence) {
    // Support senteces with or without the starting dollar sign.
    if(*sentence == '$') sentence++;

    uint8_t checksum = 0x00;

    // The optional checksum is an XOR of all bytes between "$" and "*".
    while(*sentence && *sentence != '*') checksum ^= *sentence++;

    return checksum;
}

bool minmea_check(const char* sentence, bool strict) {
    uint8_t checksum = 0x00;

    // A valid sentence starts with "$".
    if(*sentence++ != '$') return false;

    // The optional checksum is an XOR of all bytes between "$" and "*".
    while(*sentence && *sentence != '*' && isprint((unsigned char)*sentence))
        checksum ^= *sentence++;

    // If checksum is present...
    if(*sentence == '*') {
        // Extract checksum.
        sentence++;
        int upper = hex2int(*sentence++);
        if(upper == -1) return false;
        int lower = hex2int(*sentence++);
        if(lower == -1) return false;
        int expected = upper << 4 | lower;

        // Check for checksum mismatch.
        if(checksum != expected) return false;
    } else if(strict) {
        // Discard non-checksummed frames in strict mode.
        return false;
    }

    // The only stuff allowed at this point is a newline.
    while(*sentence == '\r' || *sentence == '\n') {
        sentence++;
    }

    if(*sentence) {
        return false;
    }

    return true;
}

bool minmea_scan(const char* sentence, const char* format, ...) {
    bool result = false;
    bool optional = false;

    if(sentence == NULL) return false;

    va_list ap;
    va_start(ap, format);

    const char* field = sentence;
#define next_field()                                 \
    do {                                             \
        /* Progress to the next field. */            \
        while(minmea_isfield(*sentence)) sentence++; \
        /* Make sure there is a field there. */      \
        if(*sentence == ',') {                       \
            sentence++;                              \
            field = sentence;                        \
        } else {                                     \
            field = NULL;                            \
        }                                            \
    } while(0)

    while(*format) {
        char type = *format++;

        if(type == ';') {
            // All further fields are optional.
            optional = true;
            continue;
        }

        if(!field && !optional) {
            // Field requested but we ran out if input. Bail out.
            goto parse_error;
        }

        switch(type) {
        case 'c': { // Single character field (char).
            char value = '\0';

            if(field && minmea_isfield(*field)) value = *field;

            *va_arg(ap, char*) = value;
        } break;

        case 'd': { // Single character direction field (int).
            int value = 0;

            if(field && minmea_isfield(*field)) {
                switch(*field) {
                case 'N':
                case 'E':
                    value = 1;
                    break;
                case 'S':
                case 'W':
                    value = -1;
                    break;
                default:
                    goto parse_error;
                }
            }

            *va_arg(ap, int*) = value;
        } break;

        case 'f': { // Fractional value with scale (struct minmea_float).
            int sign = 0;
            int_least32_t value = -1;
            int_least32_t scale = 0;

            if(field) {
                while(minmea_isfield(*field)) {
                    if(*field == '+' && !sign && value == -1) {
                        sign = 1;
                    } else if(*field == '-' && !sign && value == -1) {
                        sign = -1;
                    } else if(isdigit((unsigned char)*field)) {
                        int digit = *field - '0';
                        if(value == -1) value = 0;
                        if(value > (INT_LEAST32_MAX - digit) / 10) {
                            /* we ran out of bits, what do we do? */
                            if(scale) {
                                /* truncate extra precision */
                                break;
                            } else {
                                /* integer overflow. bail out. */
                                goto parse_error;
                            }
                        }
                        value = (10 * value) + digit;
                        if(scale) scale *= 10;
                    } else if(*field == '.' && scale == 0) {
                        scale = 1;
                    } else if(*field == ' ') {
                        /* Allow spaces at the start of the field. Not NMEA
                             * conformant, but some modules do this. */
                        if(sign != 0 || value != -1 || scale != 0) goto parse_error;
                    } else {
                        goto parse_error;
                    }
                    field++;
                }
            }

            if((sign || scale) && value == -1) goto parse_error;

            if(value == -1) {
                /* No digits were scanned. */
                value = 0;
                scale = 0;
            } else if(scale == 0) {
                /* No decimal point. */
                scale = 1;
            }
            if(sign) value *= sign;

            *va_arg(ap, struct minmea_float*) = (struct minmea_float){value, scale};
        } break;

        case 'i': { // Integer value, default 0 (int).
            int value = 0;

            if(field) {
                char* endptr;
                value = strtol(field, &endptr, 10);
                if(minmea_isfield(*endptr)) goto parse_error;
            }

            *va_arg(ap, int*) = value;
        } break;

        case 's': { // String value (char *).
            char* buf = va_arg(ap, char*);

            if(field) {
                while(minmea_isfield(*field)) *buf++ = *field++;
            }

            *buf = '\0';
        } break;

        case 't': { // NMEA talker+sentence identifier (char *).
            // This field is always mandatory.
            if(!field) goto parse_error;

            if(field[0] != '$') goto parse_error;
            for(int f = 0; f < 5; f++)
                if(!minmea_isfield(field[1 + f])) goto parse_error;

            char* buf = va_arg(ap, char*);
            memcpy(buf, field + 1, 5);
            buf[5] = '\0';
        } break;

        case 'D': { // Date (int, int, int), -1 if empty.
            struct minmea_date* date = va_arg(ap, struct minmea_date*);

            int d = -1, m = -1, y = -1;

            if(field && minmea_isfield(*field)) {
                // Always six digits.
                for(int f = 0; f < 6; f++)
                    if(!isdigit((unsigned char)field[f])) goto parse_error;

                char dArr[] = {field[0], field[1], '\0'};
                char mArr[] = {field[2], field[3], '\0'};
                char yArr[] = {field[4], field[5], '\0'};
                d = strtol(dArr, NULL, 10);
                m = strtol(mArr, NULL, 10);
                y = strtol(yArr, NULL, 10);
            }

            date->day = d;
            date->month = m;
            date->year = y;
        } break;

        case 'T': { // Time (int, int, int, int), -1 if empty.
            struct minmea_time* time_ = va_arg(ap, struct minmea_time*);

            int h = -1, i = -1, s = -1, u = -1;

            if(field && minmea_isfield(*field)) {
                // Minimum required: integer time.
                for(int f = 0; f < 6; f++)
                    if(!isdigit((unsigned char)field[f])) goto parse_error;

                char hArr[] = {field[0], field[1], '\0'};
                char iArr[] = {field[2], field[3], '\0'};
                char sArr[] = {field[4], field[5], '\0'};
                h = strtol(hArr, NULL, 10);
                i = strtol(iArr, NULL, 10);
                s = strtol(sArr, NULL, 10);
                field += 6;

                // Extra: fractional time. Saved as microseconds.
                if(*field++ == '.') {
                    uint32_t value = 0;
                    uint32_t scale = 1000000LU;
                    while(isdigit((unsigned char)*field) && scale > 1) {
                        value = (value * 10) + (*field++ - '0');
                        scale /= 10;
                    }
                    u = value * scale;
                } else {
                    u = 0;
                }
            }

            time_->hours = h;
            time_->minutes = i;
            time_->seconds = s;
            time_->microseconds = u;
        } break;

        case '_': { // Ignore the field.
        } break;

        default: { // Unknown.
            goto parse_error;
        }
        }

        next_field();
    }

    result = true;

parse_error:
    va_end(ap);
    return result;
}

bool minmea_talker_id(char talker[3], const char* sentence) {
    char type[6];
    if(!minmea_scan(sentence, "t", type)) return false;

    talker[0] = type[0];
    talker[1] = type[1];
    talker[2] = '\0';

    return true;
}

enum minmea_sentence_id minmea_sentence_id(const char* sentence, bool strict) {
    if(!minmea_check(sentence, strict)) return MINMEA_INVALID;

    char type[6];
    if(!minmea_scan(sentence, "t", type)) return MINMEA_INVALID;

    if(!strcmp(type + 2, "GBS")) return MINMEA_SENTENCE_GBS;
    if(!strcmp(type + 2, "GGA")) return MINMEA_SENTENCE_GGA;
    if(!strcmp(type + 2, "GLL")) return MINMEA_SENTENCE_GLL;
    if(!strcmp(type + 2, "GSA")) return MINMEA_SENTENCE_GSA;
    if(!strcmp(type + 2, "GST")) return MINMEA_SENTENCE_GST;
    if(!strcmp(type + 2, "GSV")) return MINMEA_SENTENCE_GSV;
    if(!strcmp(type + 2, "RMC")) return MINMEA_SENTENCE_RMC;
    if(!strcmp(type + 2, "VTG")) return MINMEA_SENTENCE_VTG;
    if(!strcmp(type + 2, "ZDA")) return MINMEA_SENTENCE_ZDA;

    return MINMEA_UNKNOWN;
}

bool minmea_parse_gbs(struct minmea_sentence_gbs* frame, const char* sentence) {
    // $GNGBS,170556.00,3.0,2.9,8.3,,,,*5C
    char type[6];
    if(!minmea_scan(
           sentence,
           "tTfffifff",
           type,
           &frame->time,
           &frame->err_latitude,
           &frame->err_longitude,
           &frame->err_altitude,
           &frame->svid,
           &frame->prob,
           &frame->bias,
           &frame->stddev))
        return false;
    if(strcmp(type + 2, "GBS")) return false;

    return true;
}

bool minmea_parse_rmc(struct minmea_sentence_rmc* frame, const char* sentence) {
    // $GPRMC,081836,A,3751.65,S,14507.36,E,000.0,360.0,130998,011.3,E*62
    char type[6];
    char validity;
    int latitude_direction;
    int longitude_direction;
    int variation_direction;
    if(!minmea_scan(
           sentence,
           "tTcfdfdffDfd",
           type,
           &frame->time,
           &validity,
           &frame->latitude,
           &latitude_direction,
           &frame->longitude,
           &longitude_direction,
           &frame->speed,
           &frame->course,
           &frame->date,
           &frame->variation,
           &variation_direction))
        return false;
    if(strcmp(type + 2, "RMC")) return false;

    frame->valid = (validity == 'A');
    frame->latitude.value *= latitude_direction;
    frame->longitude.value *= longitude_direction;
    frame->variation.value *= variation_direction;

    return true;
}

bool minmea_parse_gga(struct minmea_sentence_gga* frame, const char* sentence) {
    // $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
    char type[6];
    int latitude_direction;
    int longitude_direction;

    if(!minmea_scan(
           sentence,
           "tTfdfdiiffcfcf_",
           type,
           &frame->time,
           &frame->latitude,
           &latitude_direction,
           &frame->longitude,
           &longitude_direction,
           &frame->fix_quality,
           &frame->satellites_tracked,
           &frame->hdop,
           &frame->altitude,
           &frame->altitude_units,
           &frame->height,
           &frame->height_units,
           &frame->dgps_age))
        return false;
    if(strcmp(type + 2, "GGA")) return false;

    frame->latitude.value *= latitude_direction;
    frame->longitude.value *= longitude_direction;

    return true;
}

bool minmea_parse_gsa(struct minmea_sentence_gsa* frame, const char* sentence) {
    // $GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39
    char type[6];

    if(!minmea_scan(
           sentence,
           "tciiiiiiiiiiiiifff",
           type,
           &frame->mode,
           &frame->fix_type,
           &frame->sats[0],
           &frame->sats[1],
           &frame->sats[2],
           &frame->sats[3],
           &frame->sats[4],
           &frame->sats[5],
           &frame->sats[6],
           &frame->sats[7],
           &frame->sats[8],
           &frame->sats[9],
           &frame->sats[10],
           &frame->sats[11],
           &frame->pdop,
           &frame->hdop,
           &frame->vdop))
        return false;
    if(strcmp(type + 2, "GSA")) return false;

    return true;
}

bool minmea_parse_gll(struct minmea_sentence_gll* frame, const char* sentence) {
    // $GPGLL,3723.2475,N,12158.3416,W,161229.487,A,A*41$;
    char type[6];
    int latitude_direction;
    int longitude_direction;

    if(!minmea_scan(
           sentence,
           "tfdfdTc;c",
           type,
           &frame->latitude,
           &latitude_direction,
           &frame->longitude,
           &longitude_direction,
           &frame->time,
           &frame->status,
           &frame->mode))
        return false;
    if(strcmp(type + 2, "GLL")) return false;

    frame->latitude.value *= latitude_direction;
    frame->longitude.value *= longitude_direction;

    return true;
}

bool minmea_parse_gst(struct minmea_sentence_gst* frame, const char* sentence) {
    // $GPGST,024603.00,3.2,6.6,4.7,47.3,5.8,5.6,22.0*58
    char type[6];

    if(!minmea_scan(
           sentence,
           "tTfffffff",
           type,
           &frame->time,
           &frame->rms_deviation,
           &frame->semi_major_deviation,
           &frame->semi_minor_deviation,
           &frame->semi_major_orientation,
           &frame->latitude_error_deviation,
           &frame->longitude_error_deviation,
           &frame->altitude_error_deviation))
        return false;
    if(strcmp(type + 2, "GST")) return false;

    return true;
}

bool minmea_parse_gsv(struct minmea_sentence_gsv* frame, const char* sentence) {
    // $GPGSV,3,1,11,03,03,111,00,04,15,270,00,06,01,010,00,13,06,292,00*74
    // $GPGSV,3,3,11,22,42,067,42,24,14,311,43,27,05,244,00,,,,*4D
    // $GPGSV,4,2,11,08,51,203,30,09,45,215,28*75
    // $GPGSV,4,4,13,39,31,170,27*40
    // $GPGSV,4,4,13*7B
    char type[6];

    if(!minmea_scan(
           sentence,
           "tiii;iiiiiiiiiiiiiiii",
           type,
           &frame->total_msgs,
           &frame->msg_nr,
           &frame->total_sats,
           &frame->sats[0].nr,
           &frame->sats[0].elevation,
           &frame->sats[0].azimuth,
           &frame->sats[0].snr,
           &frame->sats[1].nr,
           &frame->sats[1].elevation,
           &frame->sats[1].azimuth,
           &frame->sats[1].snr,
           &frame->sats[2].nr,
           &frame->sats[2].elevation,
           &frame->sats[2].azimuth,
           &frame->sats[2].snr,
           &frame->sats[3].nr,
           &frame->sats[3].elevation,
           &frame->sats[3].azimuth,
           &frame->sats[3].snr)) {
        return false;
    }
    if(strcmp(type + 2, "GSV")) return false;

    return true;
}

bool minmea_parse_vtg(struct minmea_sentence_vtg* frame, const char* sentence) {
    // $GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48
    // $GPVTG,156.1,T,140.9,M,0.0,N,0.0,K*41
    // $GPVTG,096.5,T,083.5,M,0.0,N,0.0,K,D*22
    // $GPVTG,188.36,T,,M,0.820,N,1.519,K,A*3F
    char type[6];
    char c_true, c_magnetic, c_knots, c_kph, c_faa_mode;

    if(!minmea_scan(
           sentence,
           "t;fcfcfcfcc",
           type,
           &frame->true_track_degrees,
           &c_true,
           &frame->magnetic_track_degrees,
           &c_magnetic,
           &frame->speed_knots,
           &c_knots,
           &frame->speed_kph,
           &c_kph,
           &c_faa_mode))
        return false;
    if(strcmp(type + 2, "VTG")) return false;
    // values are only valid with the accompanying characters
    if(c_true != 'T') frame->true_track_degrees.scale = 0;
    if(c_magnetic != 'M') frame->magnetic_track_degrees.scale = 0;
    if(c_knots != 'N') frame->speed_knots.scale = 0;
    if(c_kph != 'K') frame->speed_kph.scale = 0;
    frame->faa_mode = (enum minmea_faa_mode)c_faa_mode;

    return true;
}

bool minmea_parse_zda(struct minmea_sentence_zda* frame, const char* sentence) {
    // $GPZDA,201530.00,04,07,2002,00,00*60
    char type[6];

    if(!minmea_scan(
           sentence,
           "tTiiiii",
           type,
           &frame->time,
           &frame->date.day,
           &frame->date.month,
           &frame->date.year,
           &frame->hour_offset,
           &frame->minute_offset))
        return false;
    if(strcmp(type + 2, "ZDA")) return false;

    // check offsets
    if(abs(frame->hour_offset) > 13 || frame->minute_offset > 59 || frame->minute_offset < 0)
        return false;

    return true;
}

int minmea_getdatetime(
    struct tm* tm,
    const struct minmea_date* date,
    const struct minmea_time* time_) {
    if(date->year == -1 || time_->hours == -1) return -1;

    memset(tm, 0, sizeof(*tm));
    if(date->year < 80) {
        tm->tm_year = 2000 + date->year - 1900; // 2000-2079
    } else if(date->year >= 1900) {
        tm->tm_year = date->year - 1900; // 4 digit year, use directly
    } else {
        tm->tm_year = date->year; // 1980-1999
    }
    tm->tm_mon = date->month - 1;
    tm->tm_mday = date->day;
    tm->tm_hour = time_->hours;
    tm->tm_min = time_->minutes;
    tm->tm_sec = time_->seconds;

    return 0;
}

int minmea_gettime(
    struct timespec* ts,
    const struct minmea_date* date,
    const struct minmea_time* time_) {
    struct tm tm;
    if(minmea_getdatetime(&tm, date, time_)) return -1;

    time_t timestamp = mktime(&tm); /* See README.md if your system lacks timegm(). */
    if(timestamp != (time_t)-1) {
        ts->tv_sec = timestamp;
        ts->tv_nsec = time_->microseconds * 1000;
        return 0;
    } else {
        return -1;
    }
}

/* vim: set ts=4 sw=4 et: */