nmea: parse $GPZDA sentences for date/time

Some GPS receivers only send $GPZDA sentence for date/time. Parse it
and refactor NMEA-0138 code to avoid code duplication.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

diff --git a/nmea.c b/nmea.c
index 1204c20f61eb444bf0b58b2f95c14d807c527307..5bf6d9af7124a8d82528c44ee57aaacea0316c73 100644 (file)
--- a/nmea.c
+++ b/nmea.c
@@ -66,11 +66,38 @@ nmea_txt_cb(void)
        DEBUG(3, "%s: %s\n", ids[nmea_params[3].num], nmea_params[4].str);
 }
 
+static void
+do_adjust_clock(struct tm *tm)
+{
+       char tmp[256];
+
+       strftime(tmp, 256, "%Y-%m-%dT%H:%M:%S", tm);
+       DEBUG(3, "date: %s UTC\n", tmp);
+
+       if (adjust_clock) {
+               time_t sec = timegm(tm);
+               struct timeval cur;
+
+               gettimeofday(&cur, NULL);
+
+               if ((sec < 0) || (llabs(cur.tv_sec - sec) > MAX_TIME_OFFSET)) {
+                       struct timeval tv = { 0 };
+                       tv.tv_sec = sec;
+                       if (++nmea_bad_time > MAX_BAD_TIME) {
+                               LOG("system time differs from GPS time by more than %d seconds. Using %s UTC as the new time\n", MAX_TIME_OFFSET, tmp);
+                               /* only set datetime if specified by command line argument! */
+                               settimeofday(&tv, NULL);
+                       }
+               } else {
+                       nmea_bad_time = 0;
+               }
+       }
+}
+
 static void
 nmea_rmc_cb(void)
 {
        struct tm tm;
-       char tmp[256];
 
        if (*nmea_params[2].str != 'A') {
                gps_valid = 0;
@@ -98,27 +125,7 @@ nmea_rmc_cb(void)
                tm.tm_year += 100; /* year starts with 1900 */
                tm.tm_mon -= 1; /* month starts with 0 */
 
-               strftime(tmp, 256, "%Y-%m-%dT%H:%M:%S", &tm);
-               DEBUG(3, "date: %s UTC\n", tmp);
-
-               if (adjust_clock) {
-                       time_t sec = timegm(&tm);
-                       struct timeval cur;
-
-                       gettimeofday(&cur, NULL);
-
-                       if ((sec < 0) || (llabs(cur.tv_sec - sec) > MAX_TIME_OFFSET)) {
-                               struct timeval tv = { 0 };
-                               tv.tv_sec = sec;
-                               if (++nmea_bad_time > MAX_BAD_TIME) {
-                                       LOG("system time differs from GPS time by more than %d seconds. Using %s UTC as the new time\n", MAX_TIME_OFFSET, tmp);
-                                       /* only set datetime if specified by command line argument! */
-                                       settimeofday(&tv, NULL);
-                               }
-                       } else {
-                               nmea_bad_time = 0;
-                       }
-               }
+               do_adjust_clock(&tm);
        }
 
        if (strlen(nmea_params[3].str) < 9 || strlen(nmea_params[5].str) < 10) {
@@ -151,6 +158,41 @@ nmea_rmc_cb(void)
        }
 }
 
+static void
+nmea_zda_cb(void)
+{
+       struct tm tm;
+
+       gps_valid = 1;
+
+       memset(&tm, 0, sizeof(tm));
+       tm.tm_isdst = 1;
+
+       if (sscanf(nmea_params[1].str, "%02d%02d%02d",
+               &tm.tm_hour, &tm.tm_min, &tm.tm_sec) != 3) {
+               ERROR("failed to parse time '%s'\n", nmea_params[1].str);
+               return;
+       }
+
+       if ((sscanf(nmea_params[2].str, "%02d", &tm.tm_mday) != 1) ||
+           (sscanf(nmea_params[3].str, "%02d", &tm.tm_mon) != 1) ||
+           (sscanf(nmea_params[4].str, "%04d", &tm.tm_year) != 1)) {
+               ERROR("failed to parse time '%s,%s,%s'\n",
+                       nmea_params[2].str, nmea_params[3].str, nmea_params[4].str);
+               return;
+       }
+
+       if (tm.tm_year == 0) {
+               DEBUG(4, "waiting for valid date\n");
+               return;
+       }
+
+       tm.tm_mon -= 1; /* month starts with 0 */
+       tm.tm_year -= 1900; /* full 4-digit year, tm expects years till 1900 */
+
+       do_adjust_clock(&tm);
+}
+
 static void
 nmea_gga_cb(void)
 {
@@ -192,6 +234,10 @@ static struct nmea_msg {
                .msg = "VTG",
                .cnt = 9,
                .handler = nmea_vtg_cb,
+       }, {
+               .msg = "ZDA",
+               .cnt = 5,
+               .handler = nmea_zda_cb,
        },
 };