linuxptp/pi.c

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/**
* @file pi.c
* @brief Implements a Proportional Integral clock servo.
* @note Copyright (C) 2011 Richard Cochran <richardcochran@gmail.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* 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.
*/
#include <stdlib.h>
#include <math.h>
#include "pi.h"
#include "print.h"
#include "servo_private.h"
#define HWTS_KP_SCALE 0.7
#define HWTS_KI_SCALE 0.3
#define SWTS_KP_SCALE 0.1
#define SWTS_KI_SCALE 0.001
#define MAX_KP_NORM_MAX 1.0
#define MAX_KI_NORM_MAX 2.0
#define FREQ_EST_MARGIN 0.001
/* These take their values from the configuration file. (see ptp4l.c) */
double configured_pi_kp = 0.0;
double configured_pi_ki = 0.0;
double configured_pi_kp_scale = 0.0;
double configured_pi_kp_exponent = -0.3;
double configured_pi_kp_norm_max = 0.7;
double configured_pi_ki_scale = 0.0;
double configured_pi_ki_exponent = 0.4;
double configured_pi_ki_norm_max = 0.3;
struct pi_servo {
struct servo servo;
int64_t offset[2];
uint64_t local[2];
double drift;
double kp;
double ki;
double last_freq;
int count;
};
static void pi_destroy(struct servo *servo)
{
struct pi_servo *s = container_of(servo, struct pi_servo, servo);
free(s);
}
static double pi_sample(struct servo *servo,
int64_t offset,
uint64_t local_ts,
enum servo_state *state)
{
struct pi_servo *s = container_of(servo, struct pi_servo, servo);
double ki_term, ppb = s->last_freq;
double freq_est_interval, localdiff;
switch (s->count) {
case 0:
s->offset[0] = offset;
s->local[0] = local_ts;
*state = SERVO_UNLOCKED;
s->count = 1;
break;
case 1:
s->offset[1] = offset;
s->local[1] = local_ts;
/* Make sure the first sample is older than the second. */
if (s->local[0] >= s->local[1]) {
*state = SERVO_UNLOCKED;
s->count = 0;
break;
}
/* Wait long enough before estimating the frequency offset. */
localdiff = (s->local[1] - s->local[0]) / 1e9;
localdiff += localdiff * FREQ_EST_MARGIN;
freq_est_interval = 0.016 / s->ki;
if (freq_est_interval > 1000.0) {
freq_est_interval = 1000.0;
}
if (localdiff < freq_est_interval) {
*state = SERVO_UNLOCKED;
break;
}
/* Adjust drift by the measured frequency offset. */
s->drift += (1e9 - s->drift) * (s->offset[1] - s->offset[0]) /
(s->local[1] - s->local[0]);
if (s->drift < -servo->max_frequency)
s->drift = -servo->max_frequency;
else if (s->drift > servo->max_frequency)
s->drift = servo->max_frequency;
if ((servo->first_update &&
servo->first_step_threshold &&
servo->first_step_threshold < fabs(offset)) ||
(servo->step_threshold &&
servo->step_threshold < fabs(offset)))
*state = SERVO_JUMP;
else
*state = SERVO_LOCKED;
ppb = s->drift;
s->count = 2;
break;
case 2:
/*
* reset the clock servo when offset is greater than the max
* offset value. Note that the clock jump will be performed in
* step 1, so it is not necessary to have clock jump
* immediately. This allows re-calculating drift as in initial
* clock startup.
*/
if (servo->step_threshold &&
servo->step_threshold < fabs(offset)) {
*state = SERVO_UNLOCKED;
s->count = 0;
break;
}
ki_term = s->ki * offset;
ppb = s->kp * offset + s->drift + ki_term;
if (ppb < -servo->max_frequency) {
ppb = -servo->max_frequency;
} else if (ppb > servo->max_frequency) {
ppb = servo->max_frequency;
} else {
s->drift += ki_term;
}
*state = SERVO_LOCKED;
break;
}
s->last_freq = ppb;
return ppb;
}
static void pi_sync_interval(struct servo *servo, double interval)
{
struct pi_servo *s = container_of(servo, struct pi_servo, servo);
s->kp = configured_pi_kp_scale * pow(interval, configured_pi_kp_exponent);
if (s->kp > configured_pi_kp_norm_max / interval)
s->kp = configured_pi_kp_norm_max / interval;
s->ki = configured_pi_ki_scale * pow(interval, configured_pi_ki_exponent);
if (s->ki > configured_pi_ki_norm_max / interval)
s->ki = configured_pi_ki_norm_max / interval;
pr_debug("PI servo: sync interval %.3f kp %.3f ki %.6f",
interval, s->kp, s->ki);
}
static void pi_reset(struct servo *servo)
{
struct pi_servo *s = container_of(servo, struct pi_servo, servo);
s->count = 0;
}
struct servo *pi_servo_create(int fadj, int sw_ts)
{
struct pi_servo *s;
s = calloc(1, sizeof(*s));
if (!s)
return NULL;
s->servo.destroy = pi_destroy;
s->servo.sample = pi_sample;
s->servo.sync_interval = pi_sync_interval;
s->servo.reset = pi_reset;
s->drift = fadj;
s->last_freq = fadj;
s->kp = 0.0;
s->ki = 0.0;
if (configured_pi_kp && configured_pi_ki) {
/* Use the constants as configured by the user without
adjusting for sync interval unless they make the servo
unstable. */
configured_pi_kp_scale = configured_pi_kp;
configured_pi_ki_scale = configured_pi_ki;
configured_pi_kp_exponent = 0.0;
configured_pi_ki_exponent = 0.0;
configured_pi_kp_norm_max = MAX_KP_NORM_MAX;
configured_pi_ki_norm_max = MAX_KI_NORM_MAX;
} else if (!configured_pi_kp_scale || !configured_pi_ki_scale) {
if (sw_ts) {
configured_pi_kp_scale = SWTS_KP_SCALE;
configured_pi_ki_scale = SWTS_KI_SCALE;
} else {
configured_pi_kp_scale = HWTS_KP_SCALE;
configured_pi_ki_scale = HWTS_KI_SCALE;
}
}
return &s->servo;
}