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