refclock: add option to filter wrong pulse edges

Add width option to the refclock directive to set expected width of
pulses in a PPS signal. The width adds a limit for the maximum offset
and root distance in order to reject PPS samples from wrong events, e.g.
PHCs which cannot be configured to timestamp only rising of falling
edges.

conf.c

@@ -676,7 +676,7 @@ parse_refclock(char *line)
   int n, poll, dpoll, filter_length, pps_rate, min_samples, max_samples, sel_options;
   int max_lock_age, pps_forced;
   uint32_t ref_id, lock_ref_id;
-  double offset, delay, precision, max_dispersion;
+  double offset, delay, precision, max_dispersion, pulse_width;
   char *p, *cmd, *name, *param;
   unsigned char ref[5];
   RefclockParameters *refclock;
@@ -693,6 +693,7 @@ parse_refclock(char *line)
   delay = 1e-9;
   precision = 0.0;
   max_dispersion = 0.0;
+  pulse_width = 0.0;
   ref_id = 0;
   max_lock_age = 2;
   lock_ref_id = 0;
@@ -766,6 +767,9 @@ parse_refclock(char *line)
     } else if (!strcasecmp(cmd, "maxdispersion")) {
       if (sscanf(line, "%lf%n", &max_dispersion, &n) != 1)
         break;
+    } else if (!strcasecmp(cmd, "width")) {
+      if (sscanf(line, "%lf%n", &pulse_width, &n) != 1)
+        break;
     } else if (!strcasecmp(cmd, "noselect")) {
       n = 0;
       sel_options |= SRC_SELECT_NOSELECT;
@@ -804,6 +808,7 @@ parse_refclock(char *line)
   refclock->delay = delay;
   refclock->precision = precision;
   refclock->max_dispersion = max_dispersion;
+  refclock->pulse_width = pulse_width;
   refclock->ref_id = ref_id;
   refclock->max_lock_age = max_lock_age;
   refclock->lock_ref_id = lock_ref_id;

refclock.c

@@ -85,6 +85,7 @@ struct RCL_Instance_Record {
   double offset;
   double delay;
   double precision;
+  double pulse_width;
   SCH_TimeoutID timeout_id;
   SRC_Instance source;
 };
@@ -208,6 +209,7 @@ RCL_AddRefclock(RefclockParameters *params)
   inst->delay = params->delay;
   if (params->precision > 0.0)
     inst->precision = params->precision;
+  inst->pulse_width = params->pulse_width;
   inst->timeout_id = -1;
   inst->source = NULL;
 
@@ -415,6 +417,27 @@ RCL_AddPulse(RCL_Instance instance, struct timespec *pulse_time, double second)
   return RCL_AddCookedPulse(instance, &cooked_time, second, dispersion, correction);
 }
 
+static int
+check_pulse_edge(RCL_Instance instance, double offset, double distance)
+{
+  double max_error;
+
+  if (instance->pulse_width <= 0.0)
+    return 1;
+
+  max_error = 1.0 / instance->pps_rate - instance->pulse_width;
+  max_error = MIN(instance->pulse_width, max_error);
+  max_error *= 0.5;
+
+  if (fabs(offset) > max_error || distance > max_error) {
+      DEBUG_LOG("refclock pulse ignored offset=%.9f distance=%.9f max_error=%.9f",
+                offset, distance, max_error);
+      return 0;
+  }
+
+  return 1;
+}
+
 int
 RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
                    double second, double dispersion, double raw_correction)
@@ -476,6 +499,9 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
       return 0;
     }
 
+    if (!check_pulse_edge(instance, ref_offset - offset, 0.0))
+      return 0;
+
     leap = lock_refclock->leap_status;
 
     DEBUG_LOG("refclock pulse offset=%.9f offdiff=%.9f samplediff=%.9f",
@@ -500,6 +526,9 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
       filter_reset(&instance->filter);
       return 0;
     }
+
+    if (!check_pulse_edge(instance, offset, distance))
+      return 0;
   }
 
   filter_add_sample(&instance->filter, cooked_time, offset, dispersion);

refclock.h

@@ -49,6 +49,7 @@ typedef struct {
   double delay;
   double precision;
   double max_dispersion;
+  double pulse_width;
 } RefclockParameters;
 
 typedef struct RCL_Instance_Record *RCL_Instance;