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 _DEFAULT_SOURCE
  20 #define _XOPEN_SOURCE
  21 #define _BSD_SOURCE
  22 #include <time.h>
  23
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26 #include <sys/ioctl.h>
  27 #include <sys/time.h>
  28
  29 #include <fcntl.h>
  30 #include <time.h>
  31 #include <stdlib.h>
  32 #include <stdio.h>
  33 #include <unistd.h>
  34 #include <errno.h>
  35 #include <math.h>
  36
  37 #include <string.h>
  38 #include <termios.h>
  39
  40 #include <libubox/utils.h>
  41
  42 #include "log.h"
  43 #include "nmea.h"
  44
  45 #define MAX_NMEA_PARAM  20
  46 #define MAX_TIME_OFFSET 5
  47 #define MAX_BAD_TIME    3
  48
  49 struct nmea_param {
  50         char *str;
  51         int num;
  52 } nmea_params[MAX_NMEA_PARAM];
  53
  54 static int nmea_bad_time;
  55 char longitude[33] = { 0 }, latitude[33] = { 0 }, course[17] = { 0 }, speed[17] = { 0 }, elevation[17] = { 0 };
  56 int gps_valid = 0;
  57
  58 static void
  59 nmea_txt_cb(void)
  60 {
  61         char *ids[] = { "ERROR", "WARNING", "NOTICE", };
  62
  63         if (nmea_params[3].num < 0 || nmea_params[3].num > 2)
  64                 nmea_params[3].num = 0;
  65
  66         DEBUG(3, "%s: %s\n", ids[nmea_params[3].num], nmea_params[4].str);
  67 }
  68
  69 static void
  70 do_adjust_clock(struct tm *tm)
  71 {
  72         char tmp[256];
  73
  74         strftime(tmp, 256, "%Y-%m-%dT%H:%M:%S", tm);
  75         DEBUG(3, "date: %s UTC\n", tmp);
  76
  77         if (adjust_clock) {
  78                 time_t sec = timegm(tm);
  79                 struct timeval cur;
  80
  81                 gettimeofday(&cur, NULL);
  82
  83                 if ((sec < 0) || (llabs(cur.tv_sec - sec) > MAX_TIME_OFFSET)) {
  84                         struct timeval tv = { 0 };
  85                         tv.tv_sec = sec;
  86                         if (++nmea_bad_time > MAX_BAD_TIME) {
  87                                 LOG("system time differs from GPS time by more than %d seconds. Using %s UTC as the new time\n", MAX_TIME_OFFSET, tmp);
  88                                 /* only set datetime if specified by command line argument! */
  89                                 settimeofday(&tv, NULL);
  90                         }
  91                 } else {
  92                         nmea_bad_time = 0;
  93                 }
  94         }
  95 }
  96
  97 static void
  98 nmea_rmc_cb(void)
  99 {
 100         struct tm tm;
 101
 102         if (*nmea_params[2].str != 'A') {
 103                 gps_valid = 0;
 104                 DEBUG(4, "waiting for valid signal\n");
 105                 return;
 106         }
 107
 108         gps_valid = 1;
 109         memset(&tm, 0, sizeof(tm));
 110         tm.tm_isdst = 1;
 111
 112         if (sscanf(nmea_params[1].str, "%02d%02d%02d",
 113                 &tm.tm_hour, &tm.tm_min, &tm.tm_sec) != 3) {
 114                 ERROR("failed to parse time '%s'\n", nmea_params[1].str);
 115         }
 116         else if (sscanf(nmea_params[9].str, "%02d%02d%02d",
 117                 &tm.tm_mday, &tm.tm_mon, &tm.tm_year) != 3) {
 118                 ERROR("failed to parse date '%s'\n", nmea_params[9].str);
 119         }
 120         else if (tm.tm_year == 0) {
 121                 DEBUG(4, "waiting for valid date\n");
 122                 return;
 123         }
 124         else {
 125                 tm.tm_year += 100; /* year starts with 1900 */
 126                 tm.tm_mon -= 1; /* month starts with 0 */
 127
 128                 do_adjust_clock(&tm);
 129         }
 130
 131         if (strlen(nmea_params[3].str) < 9 || strlen(nmea_params[5].str) < 10) {
 132                 ERROR("lat/lng have invalid string length %zu<9, %zu<10\n",
 133                        strlen(nmea_params[3].str), strlen(nmea_params[5].str));
 134         } else {
 135                 float minutes;
 136                 float degrees;
 137                 float lat = strtof(nmea_params[3].str, NULL);
 138                 float lon = strtof(nmea_params[5].str, NULL);
 139
 140                 degrees = floor(lat / 100.0);
 141                 minutes = lat - (degrees * 100.0);
 142                 lat = degrees + minutes / 60.0;
 143
 144                 degrees = floor(lon / 100.0);
 145                 minutes = lon - (degrees * 100.0);
 146                 lon = degrees + minutes / 60.0;
 147
 148                 if (*nmea_params[4].str == 'S')
 149                         lat *= -1.0;
 150                 if (*nmea_params[6].str == 'W')
 151                         lon *= -1.0;
 152
 153                 snprintf(latitude, sizeof(latitude), "%f", lat);
 154                 snprintf(longitude, sizeof(longitude), "%f", lon);
 155
 156                 DEBUG(3, "position: %s %s\n", latitude, longitude);
 157                 gps_timestamp();
 158         }
 159 }
 160
 161 static void
 162 nmea_zda_cb(void)
 163 {
 164         struct tm tm;
 165
 166         gps_valid = 1;
 167
 168         memset(&tm, 0, sizeof(tm));
 169         tm.tm_isdst = 1;
 170
 171         if (sscanf(nmea_params[1].str, "%02d%02d%02d",
 172                 &tm.tm_hour, &tm.tm_min, &tm.tm_sec) != 3) {
 173                 ERROR("failed to parse time '%s'\n", nmea_params[1].str);
 174                 return;
 175         }
 176
 177         if ((sscanf(nmea_params[2].str, "%02d", &tm.tm_mday) != 1) ||
 178             (sscanf(nmea_params[3].str, "%02d", &tm.tm_mon) != 1) ||
 179             (sscanf(nmea_params[4].str, "%04d", &tm.tm_year) != 1)) {
 180                 ERROR("failed to parse time '%s,%s,%s'\n",
 181                         nmea_params[2].str, nmea_params[3].str, nmea_params[4].str);
 182                 return;
 183         }
 184
 185         if (tm.tm_year == 0) {
 186                 DEBUG(4, "waiting for valid date\n");
 187                 return;
 188         }
 189
 190         tm.tm_mon -= 1; /* month starts with 0 */
 191         tm.tm_year -= 1900; /* full 4-digit year, tm expects years till 1900 */
 192
 193         do_adjust_clock(&tm);
 194 }
 195
 196 static void
 197 nmea_gga_cb(void)
 198 {
 199         if (!gps_valid)
 200                 return;
 201         strncpy(elevation, nmea_params[9].str, sizeof(elevation));
 202         DEBUG(4, "height: %s\n", elevation);
 203 }
 204
 205 static void
 206 nmea_vtg_cb(void)
 207 {
 208         if (!gps_valid)
 209                 return;
 210         strncpy(course, nmea_params[1].str, sizeof(course));
 211         strncpy(speed, nmea_params[7].str, sizeof(speed));
 212         DEBUG(4, "course: %s\n", course);
 213         DEBUG(4, "speed: %s\n", speed);
 214 }
 215
 216 static struct nmea_msg {
 217         char *msg;
 218         int cnt;
 219         void (*handler) (void);
 220 } nmea_msgs[] = {
 221         {
 222                 .msg = "TXT",
 223                 .cnt = 5,
 224                 .handler = nmea_txt_cb,
 225         }, {
 226                 .msg = "RMC",
 227                 .cnt = 11,
 228                 .handler = nmea_rmc_cb,
 229         }, {
 230                 .msg = "GGA",
 231                 .cnt = 14,
 232                 .handler = nmea_gga_cb,
 233         }, {
 234                 .msg = "VTG",
 235                 .cnt = 9,
 236                 .handler = nmea_vtg_cb,
 237         }, {
 238                 .msg = "ZDA",
 239                 .cnt = 5,
 240                 .handler = nmea_zda_cb,
 241         },
 242 };
 243
 244 static int
 245 nmea_verify_checksum(char *s)
 246 {
 247         char *csum = strrchr(s, '*');
 248         int isum, c = 0;
 249
 250         if (!csum)
 251                 return -1;
 252
 253         *csum = '\0';
 254         csum++;
 255         isum = strtol(csum, NULL, 16);
 256
 257         while(*s)
 258                 c ^= *s++;
 259
 260         if (isum != c)
 261                 return -1;
 262
 263         return 0;
 264 }
 265
 266 static int
 267 nmea_tokenize(char *msg)
 268 {
 269         int cnt = 0;
 270         char *tok = strsep(&msg, ",");
 271
 272         while (tok && cnt < MAX_NMEA_PARAM) {
 273                 nmea_params[cnt].str = tok;
 274                 nmea_params[cnt].num = atoi(tok);
 275                 cnt++;
 276                 tok = strsep(&msg, ",");
 277         }
 278
 279         return cnt;
 280 }
 281
 282 static void
 283 nmea_process(char *a)
 284 {
 285         char *csum;
 286         int cnt;
 287         unsigned int i;
 288
 289         if (strncmp(a, "$GP", 3))
 290                 return;
 291
 292         a++;
 293         csum = strrchr(a, '*');
 294         if (!csum)
 295                 return;
 296
 297         if (nmea_verify_checksum(a)) {
 298                 ERROR("nmea message has invalid checksum\n");
 299                 return;
 300         }
 301
 302         cnt = nmea_tokenize(&a[2]);
 303         if (cnt < 0) {
 304                 ERROR("failed to tokenize %s\n", a);\
 305                 return;
 306         }
 307
 308         for (i = 0; i < ARRAY_SIZE(nmea_msgs); i++) {
 309                 if (strcmp(nmea_params[0].str, nmea_msgs[i].msg))
 310                         continue;
 311                 if (nmea_msgs[i].cnt <= cnt)
 312                         nmea_msgs[i].handler();
 313                 else
 314                         ERROR("%s datagram has wrong parameter count got %d but expected %d\n", nmea_msgs[i].msg, cnt, nmea_msgs[i].cnt);
 315                 return;
 316         }
 317 }
 318
 319 static int
 320 nmea_consume(struct ustream *s, char **a)
 321 {
 322         char *eol = strstr(*a, "\n");
 323
 324         if (!eol)
 325                 return -1;
 326
 327         *eol++ = '\0';
 328
 329         nmea_process(*a);
 330
 331         ustream_consume(s, eol - *a);
 332         *a = eol;
 333
 334         return 0;
 335 }
 336
 337 static void
 338 nmea_msg_cb(struct ustream *s, int bytes)
 339 {
 340         int len;
 341         char *a = ustream_get_read_buf(s, &len);
 342
 343         while (!nmea_consume(s, &a))
 344                 ;
 345 }
 346
 347 static void nmea_notify_cb(struct ustream *s)
 348 {
 349         if (!s->eof)
 350                 return;
 351
 352         ERROR("tty error, shutting down\n");
 353         exit(-1);
 354 }
 355
 356 int
 357 nmea_open(char *dev, struct ustream_fd *s, speed_t speed)
 358 {
 359         struct termios tio;
 360         int tty;
 361
 362         tty = open(dev, O_RDWR | O_NOCTTY | O_NONBLOCK);
 363         if (tty < 0) {
 364                 ERROR("%s: device open failed: %s\n", dev, strerror(errno));
 365                 return -1;
 366         }
 367
 368         tcgetattr(tty, &tio);
 369         tio.c_cflag |= CREAD;
 370         tio.c_cflag |= CS8;
 371         tio.c_iflag |= IGNPAR;
 372         tio.c_lflag &= ~(ICANON);
 373         tio.c_lflag &= ~(ECHO);
 374         tio.c_lflag &= ~(ECHOE);
 375         tio.c_lflag &= ~(ISIG);
 376         tio.c_cc[VMIN] = 1;
 377         tio.c_cc[VTIME] = 0;
 378         cfsetispeed(&tio, speed);
 379         cfsetospeed(&tio, speed);
 380         tcsetattr(tty, TCSANOW, &tio);
 381
 382         s->stream.string_data = true;
 383         s->stream.notify_read = nmea_msg_cb;
 384         s->stream.notify_state = nmea_notify_cb;
 385
 386         ustream_fd_init(s, tty);
 387
 388         tcflush(tty, TCIFLUSH);
 389
 390         return 0;
 391 }