hwclock: refactor processing of PHC readings

Move processing of PHC readings from sys_linux to hwclock, where
statistics can be collected and filtering improved.

In the PHC refclock driver accumulate the samples even if not in the
external timestamping mode to update the context which will be needed
for improved filtering.

hwclock.c

@@ -64,6 +64,9 @@ struct HCL_Instance_Record {
   /* Minimum interval between samples */
   double min_separation;
 
+  /* Expected precision of readings */
+  double precision;
+
   /* Flag indicating the offset and frequency values are valid */
   int valid_coefs;
 
@@ -92,7 +95,7 @@ handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq,
 /* ================================================== */
 
 HCL_Instance
-HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
+HCL_CreateInstance(int min_samples, int max_samples, double min_separation, double precision)
 {
   HCL_Instance clock;
 
@@ -110,6 +113,7 @@ HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
   clock->n_samples = 0;
   clock->valid_coefs = 0;
   clock->min_separation = min_separation;
+  clock->precision = precision;
 
   LCL_AddParameterChangeHandler(handle_slew, clock);
 
@@ -140,6 +144,53 @@ HCL_NeedsNewSample(HCL_Instance clock, struct timespec *now)
 
 /* ================================================== */
 
+int
+HCL_ProcessReadings(HCL_Instance clock, int n_readings, struct timespec tss[][3],
+                    struct timespec *hw_ts, struct timespec *local_ts, double *err)
+{
+  double delay, min_delay = 0.0, hw_sum, local_sum, local_prec;
+  int i, combined;
+
+  if (n_readings < 1)
+    return 0;
+
+  for (i = 0; i < n_readings; i++) {
+    delay = UTI_DiffTimespecsToDouble(&tss[i][2], &tss[i][0]);
+
+    if (delay < 0.0) {
+      /* Step in the middle of a reading? */
+      DEBUG_LOG("Bad reading delay=%e", delay);
+      return 0;
+    }
+
+    if (i == 0 || min_delay > delay)
+      min_delay = delay;
+  }
+
+  local_prec = LCL_GetSysPrecisionAsQuantum();
+
+  /* Combine best readings */
+  for (i = combined = 0, hw_sum = local_sum = 0.0; i < n_readings; i++) {
+    delay = UTI_DiffTimespecsToDouble(&tss[i][2], &tss[i][0]);
+    if (delay > min_delay + MAX(local_prec, clock->precision))
+      continue;
+
+    hw_sum += UTI_DiffTimespecsToDouble(&tss[i][1], &tss[0][1]);
+    local_sum += UTI_DiffTimespecsToDouble(&tss[i][0], &tss[0][0]) + delay / 2.0;
+    combined++;
+  }
+
+  assert(combined);
+
+  UTI_AddDoubleToTimespec(&tss[0][1], hw_sum / combined, hw_ts);
+  UTI_AddDoubleToTimespec(&tss[0][0], local_sum / combined, local_ts);
+  *err = MAX(min_delay / 2.0, clock->precision);
+
+  return 1;
+}
+
+/* ================================================== */
+
 void
 HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,
                      struct timespec *local_ts, double err)