nmea.c

   1 /*
   2  *   This program is free software; you can redistribute it and/or modify
   3  *   it under the terms of the GNU General Public License as published by
   4  *   the Free Software Foundation; either version 2 of the License, or
   5  *   (at your option) any later version.
   6  *
   7  *   This program is distributed in the hope that it will be useful,
   8  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  *   GNU General Public License for more details.
  11  *
  12  *   You should have received a copy of the GNU General Public License
  13  *   along with this program; if not, write to the Free Software
  14  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
  15  *
  16  *   Copyright (C) 2014 John Crispin <blogic@openwrt.org>
  17  */
  18
  19 #define _BSD_SOURCE
  20 #define _XOPEN_SOURCE
  21 #include <time.h>
  22
  23 #include <sys/types.h>
  24 #include <sys/stat.h>
  25 #include <sys/ioctl.h>
  26 #include <sys/time.h>
  27
  28 #include <fcntl.h>
  29 #include <time.h>
  30 #include <stdlib.h>
  31 #include <stdio.h>
  32 #include <unistd.h>
  33
  34 #include <string.h>
  35 #include <termios.h>
  36
  37 #include <libubox/utils.h>
  38
  39 #include "log.h"
  40 #include "nmea.h"
  41
  42 #define MAX_NMEA_PARAM  20
  43 #define MAX_TIME_OFFSET 2
  44 #define MAX_BAD_TIME    3
  45
  46 struct nmea_param {
  47         char *str;
  48         int num;
  49 } nmea_params[MAX_NMEA_PARAM];
  50
  51 static int nmea_bad_time;
  52 char longitude[32] = { 0 }, latitude[32] = { 0 }, course[16] = { 0 }, speed[16] = { 0 }, elivation[16] = { 0 };
  53 int gps_valid = 0;
  54
  55 static void
  56 nmea_txt_cb(void)
  57 {
  58         char *ids[] = { "ERROR", "WARNING", "NOTICE", };
  59
  60         if (nmea_params[3].num < 0 || nmea_params[3].num > 2)
  61                 nmea_params[3].num = 0;
  62
  63         DEBUG(3, "%s: %s\n", ids[nmea_params[3].num], nmea_params[4].str);
  64 }
  65
  66 static void
  67 nmea_rmc_cb(void)
  68 {
  69         struct tm tm;
  70         char tmp[256];
  71
  72         if (*nmea_params[2].str != 'A') {
  73                 gps_valid = 0;
  74                 DEBUG(4, "waiting for valid signal\n");
  75                 return;
  76         }
  77
  78         gps_valid = 1;
  79         memset(&tm, 0, sizeof(tm));
  80         tm.tm_isdst = 1;
  81
  82         if (!strptime(nmea_params[1].str, "%H%M%S", &tm))
  83                 ERROR("failed to parse time\n");
  84         else if (!strptime(nmea_params[9].str, "%d%m%y", &tm))
  85                 ERROR("failed to parse date\n");
  86         else {
  87                 /* is there a libc api for the tz adjustment ? */
  88                 struct timeval tv = { mktime(&tm), 0 };
  89                 struct timeval cur;
  90
  91                 strftime(tmp, 256, "%D %02H:%02M:%02S", &tm);
  92                 DEBUG(3, "date: %s UTC\n", tmp);
  93
  94                 tv.tv_sec -= timezone;
  95                 if (daylight)
  96                         tv.tv_sec += 3600;
  97
  98                 gettimeofday(&cur, NULL);
  99
 100                 if (abs(cur.tv_sec - tv.tv_sec) > MAX_TIME_OFFSET) {
 101                         if (++nmea_bad_time > MAX_BAD_TIME) {
 102                                 LOG("system time differs from GPS time by more than %d seconds. Using %s UTC as the new time\n", MAX_TIME_OFFSET, tmp);
 103                                 settimeofday(&tv, NULL);
 104                         }
 105                 } else {
 106                         nmea_bad_time = 0;
 107                 }
 108         }
 109
 110         if (strlen(nmea_params[3].str) != 9 || strlen(nmea_params[5].str) != 10) {
 111                 ERROR("lat/lng have invalid string length\n");
 112         } else {
 113                 int latd, latm, lats;
 114                 int lngd, lngm, lngs;
 115                 float flats, flngs;
 116                 DEBUG(4, "position: %s, %s\n",
 117                         nmea_params[3].str, nmea_params[5].str);
 118                 latm = atoi(&nmea_params[3].str[2]);
 119                 nmea_params[3].str[2] = '\0';
 120                 latd = atoi(nmea_params[3].str);
 121                 lats = atoi(&nmea_params[3].str[5]);
 122                 if (*nmea_params[4].str != 'N')
 123                         latm *= -1;
 124
 125                 lngm = atoi(&nmea_params[5].str[3]);
 126                 nmea_params[5].str[3] = '\0';
 127                 lngd = atoi(nmea_params[5].str);
 128                 lngs = atoi(&nmea_params[5].str[6]);
 129                 if (*nmea_params[6].str != 'E')
 130                         lngm *= -1;
 131
 132                 flats = lats;
 133                 flats *= 60;
 134                 flats /= 10000;
 135
 136                 flngs = lngs;
 137                 flngs *= 60;
 138                 flngs /= 10000;
 139
 140 #define ms_to_deg(x, y) (((x * 10000) + y) / 60)
 141
 142                 DEBUG(4, "position: %d°%d.%04d, %d°%d.%04d\n",
 143                         latd, latm, lats, lngd, lngm, lngs);
 144                 DEBUG(4, "position: %d°%d'%.1f\" %d°%d'%.1f\"\n",
 145                         latd, latm, flats, lngd, lngm, flngs);
 146
 147                 snprintf(latitude, sizeof(latitude), "%d.%04d", latd, ms_to_deg(latm, lats));
 148                 snprintf(longitude, sizeof(longitude), "%d.%04d", lngd, ms_to_deg(lngm, lngs));
 149                 DEBUG(3, "position: %s %s\n", latitude, longitude);
 150                 gps_timestamp();
 151         }
 152 }
 153
 154 static void
 155 nmea_gga_cb(void)
 156 {
 157         if (!gps_valid)
 158                 return;
 159         strncpy(elivation, nmea_params[9].str, sizeof(elivation));
 160         DEBUG(4, "height: %s\n", elivation);
 161 }
 162
 163 static void
 164 nmea_vtg_cb(void)
 165 {
 166         if (!gps_valid)
 167                 return;
 168         strncpy(course, nmea_params[1].str, sizeof(course));
 169         strncpy(speed, nmea_params[6].str, sizeof(speed));
 170         DEBUG(4, "course: %s\n", course);
 171         DEBUG(4, "speed: %s\n", speed);
 172 }
 173
 174 static struct nmea_msg {
 175         char *msg;
 176         int cnt;
 177         void (*handler) (void);
 178 } nmea_msgs[] = {
 179         {
 180                 .msg = "TXT",
 181                 .cnt = 5,
 182                 .handler = nmea_txt_cb,
 183         }, {
 184                 .msg = "RMC",
 185                 .cnt = 11,
 186                 .handler = nmea_rmc_cb,
 187         }, {
 188                 .msg = "GGA",
 189                 .cnt = 14,
 190                 .handler = nmea_gga_cb,
 191         }, {
 192                 .msg = "VTG",
 193                 .cnt = 9,
 194                 .handler = nmea_vtg_cb,
 195         },
 196 };
 197
 198 static int
 199 nmea_verify_checksum(char *s)
 200 {
 201         char *csum = strrchr(s, '*');
 202         int isum, c = 0;
 203
 204         if (!csum)
 205                 return -1;
 206
 207         *csum = '\0';
 208         csum++;
 209         isum = strtol(csum, NULL, 16);
 210
 211         while(*s)
 212                 c ^= *s++;
 213
 214         if (isum != c)
 215                 return -1;
 216
 217         return 0;
 218 }
 219
 220 static int
 221 nmea_tokenize(char *msg)
 222 {
 223         int cnt = 0;
 224         char *tok = strtok(msg, ",");
 225
 226         while (tok && cnt < MAX_NMEA_PARAM) {
 227                 nmea_params[cnt].str = tok;
 228                 nmea_params[cnt].num = atoi(tok);
 229                 cnt++;
 230                 tok = strtok(NULL, ",");
 231         }
 232
 233         return cnt;
 234 }
 235
 236 static void
 237 nmea_process(char *a)
 238 {
 239         char *csum;
 240         int cnt, i;
 241
 242         if (strncmp(a, "$GP", 3))
 243                 return;
 244
 245         a++;
 246         csum = strrchr(a, '*');
 247         if (!csum)
 248                 return;
 249
 250         if (nmea_verify_checksum(a)) {
 251                 ERROR("nmea message has invlid checksum\n");
 252                 return;
 253         }
 254
 255         cnt = nmea_tokenize(&a[2]);
 256         if (cnt < 0) {
 257                 ERROR("failed to tokenize %s\n", a);\
 258                 return;
 259         }
 260
 261         for (i = 0; i < ARRAY_SIZE(nmea_msgs); i++) {
 262                 if (strcmp(nmea_params[0].str, nmea_msgs[i].msg))
 263                         continue;
 264                 if (nmea_msgs[i].cnt <= cnt)
 265                         nmea_msgs[i].handler();
 266                 else
 267                         ERROR("%s datagram has wrong parameter count got %d but expected %d\n", nmea_msgs[i].msg, cnt, nmea_msgs[i].cnt);
 268                 return;
 269         }
 270 }
 271
 272 static int
 273 nmea_consume(struct ustream *s, char **a)
 274 {
 275         char *eol = strstr(*a, "\n");
 276
 277         if (!eol)
 278                 return -1;
 279
 280         *eol++ = '\0';
 281
 282         nmea_process(*a);
 283
 284         ustream_consume(s, eol - *a);
 285         *a = eol;
 286
 287         return 0;
 288 }
 289
 290 static void
 291 nmea_msg_cb(struct ustream *s, int bytes)
 292 {
 293         int len;
 294         char *a = ustream_get_read_buf(s, &len);
 295
 296         while (!nmea_consume(s, &a))
 297                 ;
 298 }
 299
 300 static void nmea_notify_cb(struct ustream *s)
 301 {
 302         if (!s->eof)
 303                 return;
 304
 305         ERROR("tty error, shutting down\n");
 306         exit(-1);
 307 }
 308
 309 int
 310 nmea_open(char *dev, struct ustream_fd *s, speed_t speed)
 311 {
 312         struct termios tio;
 313         int tty;
 314
 315         tty = open(dev, O_RDWR | O_NOCTTY | O_NONBLOCK);
 316         if (tty < 0) {
 317                 ERROR("%s: device open failed\n", dev);
 318                 return -1;
 319         }
 320
 321         tcgetattr(tty, &tio);
 322         tio.c_cflag |= CREAD;
 323         tio.c_cflag |= CS8;
 324         tio.c_iflag |= IGNPAR;
 325         tio.c_lflag &= ~(ICANON);
 326         tio.c_lflag &= ~(ECHO);
 327         tio.c_lflag &= ~(ECHOE);
 328         tio.c_lflag &= ~(ISIG);
 329         tio.c_cc[VMIN] = 1;
 330         tio.c_cc[VTIME] = 0;
 331         cfsetispeed(&tio, speed);
 332         cfsetospeed(&tio, speed);
 333         tcsetattr(tty, TCSANOW, &tio);
 334
 335         s->stream.string_data = true;
 336         s->stream.notify_read = nmea_msg_cb;
 337         s->stream.notify_state = nmea_notify_cb;
 338
 339         ustream_fd_init(s, tty);
 340
 341         tcflush(tty, TCIFLUSH);
 342
 343         return 0;
 344 }