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 nmea_rmc_cb(void)
  71 {
  72         struct tm tm;
  73         char tmp[256];
  74
  75         if (*nmea_params[2].str != 'A') {
  76                 gps_valid = 0;
  77                 DEBUG(4, "waiting for valid signal\n");
  78                 return;
  79         }
  80
  81         gps_valid = 1;
  82         memset(&tm, 0, sizeof(tm));
  83         tm.tm_isdst = 1;
  84
  85         if (sscanf(nmea_params[1].str, "%02d%02d%02d",
  86                 &tm.tm_hour, &tm.tm_min, &tm.tm_sec) != 3) {
  87                 ERROR("failed to parse time '%s'\n", nmea_params[1].str);
  88         }
  89         else if (sscanf(nmea_params[9].str, "%02d%02d%02d",
  90                 &tm.tm_mday, &tm.tm_mon, &tm.tm_year) != 3) {
  91                 ERROR("failed to parse date '%s'\n", nmea_params[9].str);
  92         }
  93         else if (tm.tm_year == 0) {
  94                 DEBUG(4, "waiting for valid date\n");
  95                 return;
  96         }
  97         else {
  98                 tm.tm_year += 100; /* year starts with 1900 */
  99                 tm.tm_mon -= 1; /* month starts with 0 */
 100
 101                 strftime(tmp, 256, "%Y-%m-%dT%H:%M:%S", &tm);
 102                 DEBUG(3, "date: %s UTC\n", tmp);
 103
 104                 if (adjust_clock) {
 105                         time_t sec = timegm(&tm);
 106                         struct timeval cur;
 107
 108                         gettimeofday(&cur, NULL);
 109
 110                         if ((sec < 0) || (abs(cur.tv_sec - sec) > MAX_TIME_OFFSET)) {
 111                                 struct timeval tv = { 0 };
 112                                 tv.tv_sec = sec;
 113                                 if (++nmea_bad_time > MAX_BAD_TIME) {
 114                                         LOG("system time differs from GPS time by more than %d seconds. Using %s UTC as the new time\n", MAX_TIME_OFFSET, tmp);
 115                                         /* only set datetime if specified by command line argument! */
 116                                         settimeofday(&tv, NULL);
 117                                 }
 118                         } else {
 119                                 nmea_bad_time = 0;
 120                         }
 121                 }
 122         }
 123
 124         if (strlen(nmea_params[3].str) < 9 || strlen(nmea_params[5].str) < 10) {
 125                 ERROR("lat/lng have invalid string length %zu<9, %zu<10\n",
 126                        strlen(nmea_params[3].str), strlen(nmea_params[5].str));
 127         } else {
 128                 float minutes;
 129                 float degrees;
 130                 float lat = strtof(nmea_params[3].str, NULL);
 131                 float lon = strtof(nmea_params[5].str, NULL);
 132
 133                 degrees = floor(lat / 100.0);
 134                 minutes = lat - (degrees * 100.0);
 135                 lat = degrees + minutes / 60.0;
 136
 137                 degrees = floor(lon / 100.0);
 138                 minutes = lon - (degrees * 100.0);
 139                 lon = degrees + minutes / 60.0;
 140
 141                 if (*nmea_params[4].str == 'S')
 142                         lat *= -1.0;
 143                 if (*nmea_params[6].str == 'W')
 144                         lon *= -1.0;
 145
 146                 snprintf(latitude, sizeof(latitude), "%f", lat);
 147                 snprintf(longitude, sizeof(longitude), "%f", lon);
 148
 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(elevation, nmea_params[9].str, sizeof(elevation));
 160         DEBUG(4, "height: %s\n", elevation);
 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[7].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 = strsep(&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 = strsep(&msg, ",");
 231         }
 232
 233         return cnt;
 234 }
 235
 236 static void
 237 nmea_process(char *a)
 238 {
 239         char *csum;
 240         int cnt;
 241         unsigned int i;
 242
 243         if (strncmp(a, "$GP", 3))
 244                 return;
 245
 246         a++;
 247         csum = strrchr(a, '*');
 248         if (!csum)
 249                 return;
 250
 251         if (nmea_verify_checksum(a)) {
 252                 ERROR("nmea message has invalid checksum\n");
 253                 return;
 254         }
 255
 256         cnt = nmea_tokenize(&a[2]);
 257         if (cnt < 0) {
 258                 ERROR("failed to tokenize %s\n", a);\
 259                 return;
 260         }
 261
 262         for (i = 0; i < ARRAY_SIZE(nmea_msgs); i++) {
 263                 if (strcmp(nmea_params[0].str, nmea_msgs[i].msg))
 264                         continue;
 265                 if (nmea_msgs[i].cnt <= cnt)
 266                         nmea_msgs[i].handler();
 267                 else
 268                         ERROR("%s datagram has wrong parameter count got %d but expected %d\n", nmea_msgs[i].msg, cnt, nmea_msgs[i].cnt);
 269                 return;
 270         }
 271 }
 272
 273 static int
 274 nmea_consume(struct ustream *s, char **a)
 275 {
 276         char *eol = strstr(*a, "\n");
 277
 278         if (!eol)
 279                 return -1;
 280
 281         *eol++ = '\0';
 282
 283         nmea_process(*a);
 284
 285         ustream_consume(s, eol - *a);
 286         *a = eol;
 287
 288         return 0;
 289 }
 290
 291 static void
 292 nmea_msg_cb(struct ustream *s, int bytes)
 293 {
 294         int len;
 295         char *a = ustream_get_read_buf(s, &len);
 296
 297         while (!nmea_consume(s, &a))
 298                 ;
 299 }
 300
 301 static void nmea_notify_cb(struct ustream *s)
 302 {
 303         if (!s->eof)
 304                 return;
 305
 306         ERROR("tty error, shutting down\n");
 307         exit(-1);
 308 }
 309
 310 int
 311 nmea_open(char *dev, struct ustream_fd *s, speed_t speed)
 312 {
 313         struct termios tio;
 314         int tty;
 315
 316         tty = open(dev, O_RDWR | O_NOCTTY | O_NONBLOCK);
 317         if (tty < 0) {
 318                 ERROR("%s: device open failed: %s\n", dev, strerror(errno));
 319                 return -1;
 320         }
 321
 322         tcgetattr(tty, &tio);
 323         tio.c_cflag |= CREAD;
 324         tio.c_cflag |= CS8;
 325         tio.c_iflag |= IGNPAR;
 326         tio.c_lflag &= ~(ICANON);
 327         tio.c_lflag &= ~(ECHO);
 328         tio.c_lflag &= ~(ECHOE);
 329         tio.c_lflag &= ~(ISIG);
 330         tio.c_cc[VMIN] = 1;
 331         tio.c_cc[VTIME] = 0;
 332         cfsetispeed(&tio, speed);
 333         cfsetospeed(&tio, speed);
 334         tcsetattr(tty, TCSANOW, &tio);
 335
 336         s->stream.string_data = true;
 337         s->stream.notify_read = nmea_msg_cb;
 338         s->stream.notify_state = nmea_notify_cb;
 339
 340         ustream_fd_init(s, tty);
 341
 342         tcflush(tty, TCIFLUSH);
 343
 344         return 0;
 345 }