Phc2pwm is an utility program to synchronize a pwm with ptp clock
to generate PPS.
This is mainly intended for the below hardware configuration:
- A PTP supporting IP that is not capable of generating PPS signal
- A PWM signal that is connected to the above PTP hardware
- On every rising edge of PWM, PTP hardware should be able to send
the current timestamp to userspace.
- This PWM signal can be used as a PPS signal that is synchronized to
PTP clock.
Signed-off-by: Lokesh Vutla <lokeshvu...@ti.com>
---
ToDO:
- I did not really use kp and ki for calculating errors. Even without
that I could see the error within ~60ns. May be in future these
constants might be needed
- I could not fit pwm servo within existing servo implementations. Let
me know if you have any idea to do it.
makefile | 6 +-
phc2pwm.c | 233 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 237 insertions(+), 2 deletions(-)
create mode 100644 phc2pwm.c
diff --git a/makefile b/makefile
index a965bd4..4d807bd 100644
--- a/makefile
+++ b/makefile
@@ -22,7 +22,7 @@ CC = $(CROSS_COMPILE)gcc
VER = -DVER=$(version)
CFLAGS = -Wall $(VER) $(incdefs) $(DEBUG) $(EXTRA_CFLAGS)
LDLIBS = -lm -lrt $(EXTRA_LDFLAGS)
-PRG = ptp4l hwstamp_ctl nsm phc2sys phc_ctl pmc timemaster
+PRG = ptp4l hwstamp_ctl nsm phc2sys phc_ctl pmc timemaster phc2pwm
FILTERS = filter.o mave.o mmedian.o
SERVOS = linreg.o ntpshm.o nullf.o pi.o servo.o
TRANSP = raw.o transport.o udp.o udp6.o uds.o
@@ -33,7 +33,7 @@ OBJ = bmc.o clock.o clockadj.o clockcheck.o config.o
designated_fsm.o \
unicast_fsm.o unicast_service.o util.o version.o pwm.o
OBJECTS = $(OBJ) hwstamp_ctl.o nsm.o phc2sys.o phc_ctl.o pmc.o
pmc_common.o \
- sysoff.o timemaster.o
+ sysoff.o timemaster.o phc2pwm.o
SRC = $(OBJECTS:.o=.c)
DEPEND = $(OBJECTS:.o=.d)
srcdir := $(dir $(lastword $(MAKEFILE_LIST)))
@@ -60,6 +60,8 @@ phc2sys: clockadj.o clockcheck.o config.o hash.o interface.o
msg.o \
phc.o phc2sys.o pmc_common.o print.o $(SERVOS) sk.o stats.o \
sysoff.o tlv.o $(TRANSP) util.o version.o
+phc2pwm: util.o pwm.o phc2pwm.o phc.o print.o sk.o
+
hwstamp_ctl: hwstamp_ctl.o version.o
phc_ctl: phc_ctl.o phc.o sk.o util.o clockadj.o sysoff.o print.o version.o
diff --git a/phc2pwm.c b/phc2pwm.c
new file mode 100644
index 0000000..a2d9a13
--- /dev/null
+++ b/phc2pwm.c
@@ -0,0 +1,233 @@
+/**
+ * @file phc2pwm.c
+ * @brief Utility program to synchronize a pwm with ptp clock to generate PPS.
+ * This is mainly intended for the below hardware configuration:
+ * - A PTP supporting IP that is not capable of generating PPS signal
+ * - A PWM signal that is connected to the above PTP hardware
+ * - On every rising edge of PWM, PTP hardware should be able to send
+ * the current timestamp to userspace.
+ * - This PWM signal can be used as a PPS signal that is synchronized to
+ * PTP clock.
+ *
+ * @assumptions:
+ * - PWM period and duty_cycle can be updated on the fly.
+ * - Update to PWM period and duty_cycle gets reflected in next cycle.
+ *
+ * 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 <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "util.h"
+#include "pwm.h"
+#include "phc.h"
+#include "missing.h"
+#include "print.h"
+
+#define NS_PER_SEC 1000000000LL
+#define PWM_PERIOD 1000000000
+#define PWM_DUTY_CYCLE 300000000
+
+static void usage(char *progname)
+{
+ fprintf(stderr,
+ "\n"
+ "usage: %s [options]\n\n"
+ "\n"
+ " -p [dev] Clock device to use\n"
+ " -e [id] PTP index for event/trigger\n"
+ " -w [id] PWM chip device id\n"
+ " -c [id] PWM channel id from PWM chip\n"
+ " -l [num] set the logging level to 'num'\n"
+ " -h prints this message and exits\n"
+ "\n",
+ progname);
+}
+
+#define PWM_SERVO_BUF 32
+#define PWM_DRIFT_COUNT 16
+
+struct pwm_servo {
+ uint64_t period[PWM_SERVO_BUF];
+ uint64_t ts[PWM_SERVO_BUF];
+ int state;
+ int count;
+};
+
+static uint64_t pwm_servo_sample(struct pwm_servo *ps, uint64_t ts)
+{
+ double avg_period, ts_diff;
+ int offset, i, drift_cnt;
+ uint64_t period, base;
+
+ offset = ts % NS_PER_SEC;
+ if (offset > 500000000)
+ offset = offset - NS_PER_SEC;
+
+ switch (ps->state) {
+ /*
+ * Since update to PWM period gets reflected in next cycle,
+ * Servo state 0 and 1 are used to bring down the error
+ * below 1ms.
+ */
+ case 0:
+ period = ps->period[1] = PWM_PERIOD;
+ ps->state = 1;
+ break;
+ case 1:
+ if (abs(offset) < 1000000) {
+ period = ps->period[ps->count + 2] = PWM_PERIOD;
+ ps->ts[ps->count] = ts;
+ ps->state = 2;
+ ps->count++;
+ } else {
+ period = PWM_PERIOD - offset;
+ ps->state = 0;
+ }
+ break;
+ case 2:
+ /*
+ * Offset is calculated in 2 different methods:
+ * - samples collected are < PWM_DRIFT_COUNT: Calculate offset
+ * based on the last 2 timestamps
+ * - samples collected are > PWM_DRIFT_COUNT: Calculate offset
+ * based on last PWM_DRIFT_COUNT timestamps.
+ */
+ ps->ts[ps->count % PWM_SERVO_BUF] = ts;
+ drift_cnt = (ps->count > PWM_DRIFT_COUNT) ? PWM_DRIFT_COUNT : 1;
+ avg_period = 0;
+ for (i = 0; i < drift_cnt; i++)
+ avg_period += ps->period[(ps->count - i) %
PWM_SERVO_BUF];
+ ts_diff = ps->ts[ps->count % PWM_SERVO_BUF] -
+ ps->ts[(ps->count - drift_cnt) % PWM_SERVO_BUF];
+
+ /*
+ * Calculate the base period based on programmed period and
+ * observed timestamps.
+ */
+ base = avg_period / (ts_diff*1e-9) + 0.5;
+
+ /*
+ * Account for the drift in current period which is programmed
+ * in last cycle.
+ * */
+ offset += ps->period[(ps->count + 1) % PWM_SERVO_BUF] - base;
+
+ period = base - offset;
+ ps->period[(ps->count + 2) % PWM_SERVO_BUF] = period;
+ ps->count++;
+
+ /* If error is out of bounds, reset the servo */
+ if (abs(offset) > 1000000) {
+ period = PWM_PERIOD;
+ ps->count = 0;
+ ps->state = 0;
+ }
+ break;
+ }
+
+ return period;
+}
+
+int main(int argc, char *argv[])
+{
+ unsigned int pwm_chip, pwm_chan, event_index;
+ int c, err, level = LOG_INFO;
+ char *progname, *ptp_dev;
+ struct pwm_chan *chan;
+ struct pwm_servo ps;
+ clockid_t clkid;
+ uint64_t ts;
+
+ handle_term_signals();
+
+ /* Process the command line arguments. */
+ progname = strrchr(argv[0], '/');
+ progname = progname ? 1+progname : argv[0];
+
+ while (EOF != (c = getopt(argc, argv, "p:e:w:c:l:h"))) {
+ switch (c) {
+ case 'p':
+ ptp_dev = optarg;
+ break;
+ case 'e':
+ event_index = atoi(optarg);
+ break;
+ case 'w':
+ pwm_chip = atoi(optarg);
+ break;
+ case 'c':
+ pwm_chan = atoi(optarg);
+ break;
+ case 'l':
+ level = atoi(optarg);
+ break;
+ case 'h':
+ usage(progname);
+ return 0;
+ case '?':
+ default:
+ usage(progname);
+ return -1;
+ }
+ }
+ handle_term_signals();
+ print_set_progname(progname);
+ print_set_level(level);
+
+ clkid = phc_open(ptp_dev);
+ if (clkid == CLOCK_INVALID)
+ return -1;
+
+ chan = pwm_chan_create(pwm_chip, pwm_chan);
+ if (!chan) {
+ err = -1;
+ goto phc_clean;
+ }
+
+ err = phc_enable_extts(clkid, event_index);
+ if (err)
+ goto pwm_chan_clean;
+
+ pwm_chan_set_period(chan, PWM_PERIOD);
+ pwm_chan_set_duty_cycle(chan, PWM_DUTY_CYCLE);
+ ps.period[0] = PWM_PERIOD;
+ ps.count = ps.state = 0;
+
+ err = pwm_chan_enable(chan);
+ if (err)
+ goto extts_clean;
+
+ while(is_running()) {
+ if (phc_read_extts(clkid, &ts))
+ continue;
+
+ fprintf(stdout, "Timestamp = %lld.%09lld\n", ts / NS_PER_SEC,
+ ts % NS_PER_SEC);
+ pwm_chan_set_period(chan, pwm_servo_sample(&ps, ts));
+ }
+
+extts_clean:
+ phc_disable_extts(clkid, event_index);
+pwm_chan_clean:
+ pwm_chan_destroy(chan);
+phc_clean:
+ phc_close(clkid);
+
+ return err;
+}
--
2.23.0
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