[gpsd-dev] [PATCH] Fix PPS with large offsets.

[Miroslav Lichvar]

This was broken by commit 575444. The check if the PPS time isn't
referenced with an old message time used PPS offset instead of the
difference between local PPS time and local time of the last message.
The PPS sample was reported via SHM or chrony socket only if the offset
was between -1 and 1000001 seconds.

Keep the local timestamp of the last fix in struct gps_device_t in
addition to the real timestamp and use it to check the PPS delay.
Rename the l_offset variable to delay to avoid further confusion.
---
 gpsd.c      |  5 +++--
 gpsd.h-tail |  5 ++++-
 gpsmon.c    |  2 +-
 ppsthread.c | 22 ++++++++++++----------
 4 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/gpsd.c b/gpsd.c
index 53d68d1..ffaf680 100644
--- a/gpsd.c
+++ b/gpsd.c
@@ -1557,7 +1557,7 @@ static void all_reports(struct gps_device_t *device, 
gps_mask_t changed)
        //gpsd_report(context.debug, LOG_PROG, "NTP: No time this packet\n");
     } else if (isnan(device->newdata.time)) {
        //gpsd_report(context.debug, LOG_PROG, "NTP: bad new time\n");
-    } else if (device->newdata.time == device->last_fixtime) {
+    } else if (device->newdata.time == device->last_fixtime.real) {
        //gpsd_report(context.debug, LOG_PROG, "NTP: Not a new time\n");
     } else if (!device->ship_to_ntpd) {
        //gpsd_report(context.debug, LOG_PROG, "NTP: No precision time 
report\n");
@@ -1588,7 +1588,8 @@ static void all_reports(struct gps_device_t *device, 
gps_mask_t changed)
        /address@hidden@*/
        (void)ntpshm_put(device, device->shmIndex, &td);
        /address@hidden@*/
-       device->last_fixtime = device->newdata.time;
+       device->last_fixtime.real = device->newdata.time;
+       device->last_fixtime.clock = td.clock.tv_sec + td.clock.tv_nsec / 1e9;
     }
 #endif /* NTPSHM_ENABLE */
 
diff --git a/gpsd.h-tail b/gpsd.h-tail
index 8040094..08e0d59 100644
--- a/gpsd.h-tail
+++ b/gpsd.h-tail
@@ -475,7 +475,10 @@ struct gps_device_t {
     int shmIndexPPS;
 # endif /* PPS_ENABLE */
 #endif /* NTPSHM_ENABLE */
-    volatile timestamp_t last_fixtime;         /* so updates happen once */
+    volatile struct {
+       timestamp_t real;
+       timestamp_t clock;
+    } last_fixtime;    /* so updates happen once */
 #ifdef PPS_ENABLE
 #if defined(HAVE_SYS_TIMEPPS_H)
     pps_handle_t kernelpps_handle;
diff --git a/gpsmon.c b/gpsmon.c
index b030979..77b6558 100644
--- a/gpsmon.c
+++ b/gpsmon.c
@@ -770,7 +770,7 @@ static void gpsmon_hook(struct gps_device_t *device, 
gps_mask_t changed UNUSED)
     report_unlock();
 
     /* Update the last fix time seen for PPS. FIXME: do this here? */
-    device->last_fixtime = device->newdata.time;
+    device->last_fixtime.real = device->newdata.time;
 }
 /address@hidden +nullpass +globstate +compdef address@hidden/
 
diff --git a/ppsthread.c b/ppsthread.c
index d9e431e..ed5c7ef 100644
--- a/ppsthread.c
+++ b/ppsthread.c
@@ -238,7 +238,7 @@ static int init_kernel_pps(struct gps_device_t *session)
 static /address@hidden@*/ void *gpsd_ppsmonitor(void *arg)
 {
     struct gps_device_t *session = (struct gps_device_t *)arg;
-    double last_fixtime = 0;
+    double last_fixtime_real = 0, last_fixtime_clock = 0;
 #ifndef HAVE_CLOCK_GETTIME
     struct timeval  clock_tv = {0, 0};
 #endif /* HAVE_CLOCK_GETTIME */
@@ -299,7 +299,8 @@ static /address@hidden@*/ void *gpsd_ppsmonitor(void *arg)
            break;
        }
         /* quick, grab a copy of last_fixtime before it changes */
-       last_fixtime = session->last_fixtime;
+       last_fixtime_real = session->last_fixtime.real;
+       last_fixtime_clock = session->last_fixtime.clock;
 
 /address@hidden@*/
         /* get the time after we just woke up */
@@ -541,7 +542,7 @@ static /address@hidden@*/ void *gpsd_ppsmonitor(void *arg)
            log = "Too long for 0.5Hz\n";
        }
 #endif /* TIOCMIWAIT */
-       if ( ok && last_second_used >= last_fixtime ) {
+       if ( ok && last_second_used >= last_fixtime_real ) {
                /* uh, oh, this second already handled */
                ok = 0;
                log = "this second already handled\n";
@@ -550,7 +551,8 @@ static /address@hidden@*/ void *gpsd_ppsmonitor(void *arg)
        if (ok) {
            /* offset is the skew from expected to observed pulse time */
            double offset;
-           long l_offset;
+           /* delay after last fix */
+           double delay;
            char *log1 = NULL;
            /* drift.real is the time we think the pulse represents  */
            struct timedrift_t drift;
@@ -580,7 +582,7 @@ static /address@hidden@*/ void *gpsd_ppsmonitor(void *arg)
              */
 
            /address@hidden@*/
-           drift.real.tv_sec = last_fixtime + 1;
+           drift.real.tv_sec = last_fixtime_real + 1;
            drift.real.tv_nsec = 0;  /* need to be fixed for 5Hz */
            drift.clock = clock_ts;
            /address@hidden@*/
@@ -589,15 +591,15 @@ static /address@hidden@*/ void *gpsd_ppsmonitor(void *arg)
             * GPS serial input then use that */
            offset = (drift.real.tv_sec - drift.clock.tv_sec);
            offset += ((drift.real.tv_nsec - drift.clock.tv_nsec) / 1e9);
-           l_offset = (long) offset;
-           if (0 > l_offset || 1000000 < l_offset) {
+           delay = (drift.clock.tv_sec + drift.clock.tv_nsec / 1e9) - 
last_fixtime_clock;
+           if (0.0 > delay || 1.0 < delay) {
                gpsd_report(session->context->debug, LOG_RAW,
-                           "PPS: no current GPS seconds: %ld\n",
-                           (long)l_offset);
+                           "PPS: no current GPS seconds: %f\n",
+                           delay);
                log1 = "timestamp out of range";
            } else {
                /address@hidden@*/
-               last_second_used = last_fixtime;
+               last_second_used = last_fixtime_real;
                if (session->thread_report_hook != NULL) 
                    log1 = session->thread_report_hook(session, &drift);
                else
-- 
1.9.0