chrony/local.c

/*
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
 * Copyright (C) Miroslav Lichvar  2011, 2014-2015
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
 * published by the Free Software Foundation.
 * 
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 * 
 **********************************************************************

  =======================================================================

  The routines in this file present a common local (system) clock
  interface to the rest of the software.

  They interface with the system specific driver files in sys_*.c
  */

#include "config.h"

#include "sysincl.h"

#include "conf.h"
#include "local.h"
#include "localp.h"
#include "memory.h"
#include "smooth.h"
#include "util.h"
#include "logging.h"

/* ================================================== */

/* Variable to store the current frequency, in ppm */
static double current_freq_ppm;

/* Maximum allowed frequency, in ppm */
static double max_freq_ppm;

/* Temperature compensation, in ppm */
static double temp_comp_ppm;

/* ================================================== */
/* Store the system dependent drivers */

static lcl_ReadFrequencyDriver drv_read_freq;
static lcl_SetFrequencyDriver drv_set_freq;
static lcl_AccrueOffsetDriver drv_accrue_offset;
static lcl_ApplyStepOffsetDriver drv_apply_step_offset;
static lcl_OffsetCorrectionDriver drv_offset_convert;
static lcl_SetLeapDriver drv_set_leap;
static lcl_SetSyncStatusDriver drv_set_sync_status;

/* ================================================== */

/* Types and variables associated with handling the parameter change
   list */

typedef struct _ChangeListEntry {
  struct _ChangeListEntry *next;
  struct _ChangeListEntry *prev;
  LCL_ParameterChangeHandler handler;
  void *anything;
} ChangeListEntry;

static ChangeListEntry change_list;

/* ================================================== */

/* Types and variables associated with handling the parameter change
   list */

typedef struct _DispersionNotifyListEntry {
  struct _DispersionNotifyListEntry *next;
  struct _DispersionNotifyListEntry *prev;
  LCL_DispersionNotifyHandler handler;
  void *anything;
} DispersionNotifyListEntry;

static DispersionNotifyListEntry dispersion_notify_list;

/* ================================================== */

static int precision_log;
static double precision_quantum;

static double max_clock_error;

#define NSEC_PER_SEC 1000000000

/* ================================================== */

/* Ask the system for the resolution of the system clock.  The Linux
   clock_getres() is not usable, because it reports the internal timer
   resolution, which is 1 ns when high-resolution timers are enabled,
   even when using a lower-resolution clocksource. */

static int
get_clock_resolution(void)
{
#if defined(HAVE_CLOCK_GETTIME) && !defined(LINUX)
  struct timespec res;

  if (clock_getres(CLOCK_REALTIME, &res) < 0)
    return 0;

  return NSEC_PER_SEC * res.tv_sec + res.tv_nsec;
#else
  return 0;
#endif
}

/* ================================================== */

#if defined(LINUX) && defined(HAVE_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC_RAW)

static int
compare_ints(const void *a, const void *b)
{
  return *(const int *)a - *(const int *)b;
}

#define READINGS 64

/* On Linux, try to measure the actual resolution of the system
   clock by performing a varying amount of busy work between clock
   readings and finding the minimum change in the measured interval.
   Require a change of at least two nanoseconds to ignore errors
   caused by conversion to timespec.  Use the raw monotonic clock
   to avoid the impact of potential frequency changes due to NTP
   adjustments made by other processes, and the kernel dithering of
   the 32-bit multiplier. */

static int
measure_clock_resolution(void)
{
  int i, j, b, busy, diffs[READINGS - 1], diff2, min;
  struct timespec start_ts, ts[READINGS];
  uint32_t acc;

  if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_ts) < 0)
    return 0;

  for (acc = 0, busy = 1; busy < 100000; busy = busy * 3 / 2 + 1) {
    for (i = 0, b = busy * READINGS; i < READINGS; i++, b -= busy) {
      if (clock_gettime(CLOCK_MONOTONIC_RAW, &ts[i]) < 0)
        return 0;

      for (j = b; j > 0; j--)
        acc += (acc & 1) + (uint32_t)ts[i].tv_nsec;
    }

    /* Give up after 0.1 seconds */
    if (UTI_DiffTimespecsToDouble(&ts[READINGS - 1], &start_ts) > 0.1) {
      DEBUG_LOG("Measurement too slow");
      return 0;
    }

    for (i = 0; i < READINGS - 1; i++) {
      diffs[i] = NSEC_PER_SEC * (ts[i + 1].tv_sec - ts[i].tv_sec) +
                 (ts[i + 1].tv_nsec - ts[i].tv_nsec);

      /* Make sure the differences are sane.  A resolution larger than the
         reading time will be measured in measure_clock_read_delay(). */
      if (diffs[i] <= 0 || diffs[i] > NSEC_PER_SEC)
        return 0;
    }

    /* Sort the differences and keep values unique within 1 ns from the
       first half of the array, which are less likely to be impacted by CPU
       interruptions */
    qsort(diffs, READINGS - 1, sizeof (diffs[0]), compare_ints);
    for (i = 1, j = 0; i < READINGS / 2; i++) {
      if (diffs[j] + 1 < diffs[i])
        diffs[++j] = diffs[i];
    }
    j++;

#if 0
    for (i = 0; i < j; i++)
      DEBUG_LOG("busy %d diff %d %d", busy, i, diffs[i]);
#endif

    /* Require at least three unique differences to be more confident
       with the result */
    if (j < 3)
      continue;

    /* Find the smallest difference between the unique differences */
    for (i = 1, min = 0; i < j; i++) {
      diff2 = diffs[i] - diffs[i - 1];
      if (min == 0 || min > diff2)
        min = diff2;
    }

    if (min == 0)
      continue;

    /* Prevent the compiler from optimising the busy work out */
    if (acc == 0)
      min += 1;

    return min;
  }

  return 0;
}

#else
static int
measure_clock_resolution(void)
{
  return 0;
}
#endif

/* ================================================== */

/* As a fallback, measure how long it takes to read the clock.  It
   typically takes longer than the resolution of the clock (and it
   depends on the CPU speed), i.e. every reading gives a different
   value, but handle also low-resolution clocks that might give
   the same reading multiple times. */

/* Define the number of increments of the system clock that we want
   to see to be fairly sure that we've got something approaching
   the minimum increment.  Even on a crummy implementation that can't
   interpolate between 10ms ticks, we should get this done in
   under 1s of busy waiting. */
#define NITERS 100

static int
measure_clock_read_delay(void)
{
  struct timespec ts, old_ts;
  int iters, diff, best;

  LCL_ReadRawTime(&old_ts);

  /* Assume we must be better than a second */
  best = NSEC_PER_SEC;
  iters = 0;

  do {
    LCL_ReadRawTime(&ts);

    diff = NSEC_PER_SEC * (ts.tv_sec - old_ts.tv_sec) + (ts.tv_nsec - old_ts.tv_nsec);

    old_ts = ts;
    if (diff > 0) {
      if (diff < best)
        best = diff;
      iters++;
    }
  } while (iters < NITERS);

  assert(best > 0);

  return best;
}

/* ================================================== */

static double
measure_clock_precision(void)
{
  int res, delay, prec;

  res = get_clock_resolution();
  if (res <= 0)
    res = measure_clock_resolution();

  delay = measure_clock_read_delay();

  if (res > 0)
    prec = MIN(res, delay);
  else
    prec = delay;

  return prec / 1.0e9;
}

/* ================================================== */

void
LCL_Initialise(void)
{
  change_list.next = change_list.prev = &change_list;

  dispersion_notify_list.next = dispersion_notify_list.prev = &dispersion_notify_list;

  /* Null out the system drivers, so that we die
     if they never get defined before use */
  
  drv_read_freq = NULL;
  drv_set_freq = NULL;
  drv_accrue_offset = NULL;
  drv_offset_convert = NULL;

  /* This ought to be set from the system driver layer */
  current_freq_ppm = 0.0;
  temp_comp_ppm = 0.0;

  precision_quantum = CNF_GetClockPrecision();
  if (precision_quantum <= 0.0)
    precision_quantum = measure_clock_precision();

  precision_quantum = CLAMP(1.0e-9, precision_quantum, 1.0);
  precision_log = round(log(precision_quantum) / log(2.0));
  /* NTP code doesn't support smaller log than -30 */
  assert(precision_log >= -30);

  DEBUG_LOG("Clock precision %.9f (%d)", precision_quantum, precision_log);

  /* This is the maximum allowed frequency offset in ppm, the time must
     never stop or run backwards */
  max_freq_ppm = CNF_GetMaxDrift();
  max_freq_ppm = CLAMP(0.0, max_freq_ppm, 500000.0);

  max_clock_error = CNF_GetMaxClockError() * 1e-6;
}

/* ================================================== */

void
LCL_Finalise(void)
{
  /* Make sure all handlers have been removed */
  BRIEF_ASSERT(change_list.next == &change_list);
  BRIEF_ASSERT(dispersion_notify_list.next == &dispersion_notify_list);
}

/* ================================================== */

/* Routine to read the system precision as a log to base 2 value. */
int
LCL_GetSysPrecisionAsLog(void)
{
  return precision_log;
}

/* ================================================== */
/* Routine to read the system precision in terms of the actual time step */

double
LCL_GetSysPrecisionAsQuantum(void)
{
  return precision_quantum;
}

/* ================================================== */

double
LCL_GetMaxClockError(void)
{
  return max_clock_error;
}

/* ================================================== */

void
LCL_AddParameterChangeHandler(LCL_ParameterChangeHandler handler, void *anything)
{
  ChangeListEntry *ptr, *new_entry;

  /* Check that the handler is not already registered */
  for (ptr = change_list.next; ptr != &change_list; ptr = ptr->next) {
    BRIEF_ASSERT(ptr->handler != handler || ptr->anything != anything);
  }

  new_entry = MallocNew(ChangeListEntry);

  new_entry->handler = handler;
  new_entry->anything = anything;

  /* Chain it into the list */
  new_entry->next = &change_list;
  new_entry->prev = change_list.prev;
  change_list.prev->next = new_entry;
  change_list.prev = new_entry;
}

/* ================================================== */

/* Remove a handler */
void LCL_RemoveParameterChangeHandler(LCL_ParameterChangeHandler handler, void *anything)
{

  ChangeListEntry *ptr;
  int ok;

  ptr = NULL;
  ok = 0;

  for (ptr = change_list.next; ptr != &change_list; ptr = ptr->next) {
    if (ptr->handler == handler && ptr->anything == anything) {
      ok = 1;
      break;
    }
  }

  assert(ok);

  /* Unlink entry from the list */
  ptr->next->prev = ptr->prev;
  ptr->prev->next = ptr->next;

  Free(ptr);
}

/* ================================================== */

int
LCL_IsFirstParameterChangeHandler(LCL_ParameterChangeHandler handler)
{
  return change_list.next->handler == handler;
}

/* ================================================== */

static void
invoke_parameter_change_handlers(struct timespec *raw, struct timespec *cooked,
                                 double dfreq, double doffset,
                                 LCL_ChangeType change_type)
{
  ChangeListEntry *ptr;

  for (ptr = change_list.next; ptr != &change_list; ptr = ptr->next) {
    (ptr->handler)(raw, cooked, dfreq, doffset, change_type, ptr->anything);
  }
}

/* ================================================== */

void
LCL_AddDispersionNotifyHandler(LCL_DispersionNotifyHandler handler, void *anything)
{
  DispersionNotifyListEntry *ptr, *new_entry;

  /* Check that the handler is not already registered */
  for (ptr = dispersion_notify_list.next; ptr != &dispersion_notify_list; ptr = ptr->next) {
    BRIEF_ASSERT(ptr->handler != handler || ptr->anything != anything);
  }

  new_entry = MallocNew(DispersionNotifyListEntry);

  new_entry->handler = handler;
  new_entry->anything = anything;

  /* Chain it into the list */
  new_entry->next = &dispersion_notify_list;
  new_entry->prev = dispersion_notify_list.prev;
  dispersion_notify_list.prev->next = new_entry;
  dispersion_notify_list.prev = new_entry;
}

/* ================================================== */

/* Remove a handler */
extern 
void LCL_RemoveDispersionNotifyHandler(LCL_DispersionNotifyHandler handler, void *anything)
{

  DispersionNotifyListEntry *ptr;
  int ok;

  ptr = NULL;
  ok = 0;

  for (ptr = dispersion_notify_list.next; ptr != &dispersion_notify_list; ptr = ptr->next) {
    if (ptr->handler == handler && ptr->anything == anything) {
      ok = 1;
      break;
    }
  }

  assert(ok);

  /* Unlink entry from the list */
  ptr->next->prev = ptr->prev;
  ptr->prev->next = ptr->next;

  Free(ptr);
}

/* ================================================== */

void
LCL_ReadRawTime(struct timespec *ts)
{
#if HAVE_CLOCK_GETTIME
  if (clock_gettime(CLOCK_REALTIME, ts) < 0)
    LOG_FATAL("clock_gettime() failed : %s", strerror(errno));
#else
  struct timeval tv;

  if (gettimeofday(&tv, NULL) < 0)
    LOG_FATAL("gettimeofday() failed : %s", strerror(errno));

  UTI_TimevalToTimespec(&tv, ts);
#endif
}

/* ================================================== */

void
LCL_ReadCookedTime(struct timespec *result, double *err)
{
  struct timespec raw;

  LCL_ReadRawTime(&raw);
  LCL_CookTime(&raw, result, err);
}

/* ================================================== */

void
LCL_CookTime(struct timespec *raw, struct timespec *cooked, double *err)
{
  double correction;

  LCL_GetOffsetCorrection(raw, &correction, err);
  UTI_AddDoubleToTimespec(raw, correction, cooked);
}

/* ================================================== */

void
LCL_GetOffsetCorrection(struct timespec *raw, double *correction, double *err)
{
  /* Call system specific driver to get correction */
  (*drv_offset_convert)(raw, correction, err);
}

/* ================================================== */
/* Return current frequency */

double
LCL_ReadAbsoluteFrequency(void)
{
  double freq;

  freq = current_freq_ppm; 

  /* Undo temperature compensation */
  if (temp_comp_ppm != 0.0) {
    freq = (freq + temp_comp_ppm) / (1.0 - 1.0e-6 * temp_comp_ppm);
  }

  return freq;
}

/* ================================================== */

static double
clamp_freq(double freq)
{
  if (freq <= max_freq_ppm && freq >= -max_freq_ppm)
    return freq;

  LOG(LOGS_WARN, "Frequency %.1f ppm exceeds allowed maximum", freq);

  return CLAMP(-max_freq_ppm, freq, max_freq_ppm);
}

/* ================================================== */

static int
check_offset(struct timespec *now, double offset)
{
  /* Check if the time will be still sane with accumulated offset */
  if (UTI_IsTimeOffsetSane(now, -offset))
      return 1;

  LOG(LOGS_WARN, "Adjustment of %.1f seconds is invalid", -offset);
  return 0;
}

/* ================================================== */

/* This involves both setting the absolute frequency with the
   system-specific driver, as well as calling all notify handlers */

void
LCL_SetAbsoluteFrequency(double afreq_ppm)
{
  struct timespec raw, cooked;
  double dfreq;
  
  afreq_ppm = clamp_freq(afreq_ppm);

  /* Apply temperature compensation */
  if (temp_comp_ppm != 0.0) {
    afreq_ppm = afreq_ppm * (1.0 - 1.0e-6 * temp_comp_ppm) - temp_comp_ppm;
  }

  /* Call the system-specific driver for setting the frequency */
  
  afreq_ppm = (*drv_set_freq)(afreq_ppm);

  dfreq = (afreq_ppm - current_freq_ppm) / (1.0e6 - current_freq_ppm);

  LCL_ReadRawTime(&raw);
  LCL_CookTime(&raw, &cooked, NULL);

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, dfreq, 0.0, LCL_ChangeAdjust);

  current_freq_ppm = afreq_ppm;

}

/* ================================================== */

void
LCL_AccumulateDeltaFrequency(double dfreq)
{
  struct timespec raw, cooked;
  double old_freq_ppm;

  old_freq_ppm = current_freq_ppm;

  /* Work out new absolute frequency.  Note that absolute frequencies
   are handled in units of ppm, whereas the 'dfreq' argument is in
   terms of the gradient of the (offset) v (local time) function. */

  current_freq_ppm += dfreq * (1.0e6 - current_freq_ppm);

  current_freq_ppm = clamp_freq(current_freq_ppm);

  /* Call the system-specific driver for setting the frequency */
  current_freq_ppm = (*drv_set_freq)(current_freq_ppm);
  dfreq = (current_freq_ppm - old_freq_ppm) / (1.0e6 - old_freq_ppm);

  LCL_ReadRawTime(&raw);
  LCL_CookTime(&raw, &cooked, NULL);

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, dfreq, 0.0, LCL_ChangeAdjust);
}

/* ================================================== */

int
LCL_AccumulateOffset(double offset, double corr_rate)
{
  struct timespec raw, cooked;

  /* In this case, the cooked time to be passed to the notify clients
     has to be the cooked time BEFORE the change was made */

  LCL_ReadRawTime(&raw);
  LCL_CookTime(&raw, &cooked, NULL);

  if (!check_offset(&cooked, offset))
    return 0;

  (*drv_accrue_offset)(offset, corr_rate);

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, 0.0, offset, LCL_ChangeAdjust);

  return 1;
}

/* ================================================== */

int
LCL_ApplyStepOffset(double offset)
{
  struct timespec raw, cooked;

  /* In this case, the cooked time to be passed to the notify clients
     has to be the cooked time BEFORE the change was made */

  LCL_ReadRawTime(&raw);
  LCL_CookTime(&raw, &cooked, NULL);

  if (!check_offset(&raw, offset))
      return 0;

  if (!(*drv_apply_step_offset)(offset)) {
    LOG(LOGS_ERR, "Could not step system clock");
    return 0;
  }

  /* Reset smoothing on all clock steps */
  SMT_Reset(&cooked);

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, 0.0, offset, LCL_ChangeStep);

  return 1;
}

/* ================================================== */

void
LCL_NotifyExternalTimeStep(struct timespec *raw, struct timespec *cooked,
    double offset, double dispersion)
{
  LCL_CancelOffsetCorrection();

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(raw, cooked, 0.0, offset, LCL_ChangeUnknownStep);

  lcl_InvokeDispersionNotifyHandlers(dispersion);
}

/* ================================================== */

void
LCL_NotifyLeap(int leap)
{
  struct timespec raw, cooked;

  LCL_ReadRawTime(&raw);
  LCL_CookTime(&raw, &cooked, NULL);

  /* Smooth the leap second out */
  SMT_Leap(&cooked, leap);

  /* Dispatch to all handlers as if the clock was stepped */
  invoke_parameter_change_handlers(&raw, &cooked, 0.0, -leap, LCL_ChangeStep);
}

/* ================================================== */

int
LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)
{
  struct timespec raw, cooked;
  double old_freq_ppm;

  LCL_ReadRawTime(&raw);
  /* Due to modifying the offset, this has to be the cooked time prior
     to the change we are about to make */
  LCL_CookTime(&raw, &cooked, NULL);

  if (!check_offset(&cooked, doffset))
    return 0;

  old_freq_ppm = current_freq_ppm;

  /* Work out new absolute frequency.  Note that absolute frequencies
   are handled in units of ppm, whereas the 'dfreq' argument is in
   terms of the gradient of the (offset) v (local time) function. */
  current_freq_ppm += dfreq * (1.0e6 - current_freq_ppm);

  current_freq_ppm = clamp_freq(current_freq_ppm);

  DEBUG_LOG("old_freq=%.3fppm new_freq=%.3fppm offset=%.6fsec",
      old_freq_ppm, current_freq_ppm, doffset);

  /* Call the system-specific driver for setting the frequency */
  current_freq_ppm = (*drv_set_freq)(current_freq_ppm);
  dfreq = (current_freq_ppm - old_freq_ppm) / (1.0e6 - old_freq_ppm);

  (*drv_accrue_offset)(doffset, corr_rate);

  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(&raw, &cooked, dfreq, doffset, LCL_ChangeAdjust);

  return 1;
}

/* ================================================== */

int
LCL_AccumulateFrequencyAndOffsetNoHandlers(double dfreq, double doffset, double corr_rate)
{
  ChangeListEntry *first_handler;
  int r;

  first_handler = change_list.next;
  change_list.next = &change_list;

  r = LCL_AccumulateFrequencyAndOffset(dfreq, doffset, corr_rate);

  change_list.next = first_handler;

  return r;
}

/* ================================================== */

void
lcl_InvokeDispersionNotifyHandlers(double dispersion)
{
  DispersionNotifyListEntry *ptr;

  for (ptr = dispersion_notify_list.next; ptr != &dispersion_notify_list; ptr = ptr->next) {
    (ptr->handler)(dispersion, ptr->anything);
  }

}

/* ================================================== */

void
lcl_RegisterSystemDrivers(lcl_ReadFrequencyDriver read_freq,
                          lcl_SetFrequencyDriver set_freq,
                          lcl_AccrueOffsetDriver accrue_offset,
                          lcl_ApplyStepOffsetDriver apply_step_offset,
                          lcl_OffsetCorrectionDriver offset_convert,
                          lcl_SetLeapDriver set_leap,
                          lcl_SetSyncStatusDriver set_sync_status)
{
  drv_read_freq = read_freq;
  drv_set_freq = set_freq;
  drv_accrue_offset = accrue_offset;
  drv_apply_step_offset = apply_step_offset;
  drv_offset_convert = offset_convert;
  drv_set_leap = set_leap;
  drv_set_sync_status = set_sync_status;

  current_freq_ppm = (*drv_read_freq)();

  DEBUG_LOG("Local freq=%.3fppm", current_freq_ppm);
}

/* ================================================== */
/* Look at the current difference between the system time and the NTP
   time, and make a step to cancel it. */

int
LCL_MakeStep(void)
{
  struct timespec raw;
  double correction;

  LCL_ReadRawTime(&raw);
  LCL_GetOffsetCorrection(&raw, &correction, NULL);

  if (!check_offset(&raw, -correction))
      return 0;

  /* Cancel remaining slew and make the step */
  LCL_AccumulateOffset(correction, 0.0);
  if (!LCL_ApplyStepOffset(-correction)) {
    /* Revert the correction */
    LCL_AccumulateOffset(-correction, 0.0);
    return 0;
  }

  LOG(LOGS_WARN, "System clock was stepped by %.6f seconds", correction);

  return 1;
}

/* ================================================== */

void
LCL_CancelOffsetCorrection(void)
{
  struct timespec raw;
  double correction;

  LCL_ReadRawTime(&raw);
  LCL_GetOffsetCorrection(&raw, &correction, NULL);
  LCL_AccumulateOffset(correction, 0.0);
}

/* ================================================== */

int
LCL_CanSystemLeap(void)
{
  return drv_set_leap ? 1 : 0;
}

/* ================================================== */

void
LCL_SetSystemLeap(int leap, int tai_offset)
{
  if (drv_set_leap) {
    (drv_set_leap)(leap, tai_offset);
  }
}

/* ================================================== */

double
LCL_SetTempComp(double comp)
{
  double uncomp_freq_ppm;

  if (temp_comp_ppm == comp)
    return comp;

  /* Undo previous compensation */
  current_freq_ppm = (current_freq_ppm + temp_comp_ppm) /
    (1.0 - 1.0e-6 * temp_comp_ppm);

  uncomp_freq_ppm = current_freq_ppm;

  /* Apply new compensation */
  current_freq_ppm = current_freq_ppm * (1.0 - 1.0e-6 * comp) - comp;

  /* Call the system-specific driver for setting the frequency */
  current_freq_ppm = (*drv_set_freq)(current_freq_ppm);

  temp_comp_ppm = (uncomp_freq_ppm - current_freq_ppm) /
    (1.0e-6 * uncomp_freq_ppm + 1.0);

  return temp_comp_ppm;
}

/* ================================================== */

void
LCL_SetSyncStatus(int synchronised, double est_error, double max_error)
{
  if (drv_set_sync_status) {
    (drv_set_sync_status)(synchronised, est_error, max_error);
  }
}

/* ================================================== */