ptp4l: add support for using configured_pi_f_offset servo option

This patch adds support for using the configured_pi_f_offset servo option to ptp4l.
If "pi_f_offset_const 0.0" is specified in the config file, stepping on the first
update is prevented. If any other positive value is specified, stepping on the
first update occurs when the offset is larger than the specified value.

change since v1
 - add the new option to default.cfg and gPTP.cfg

Signed-off-by: Ken ICHIKAWA <ichikawa.ken@jp.fujitsu.com>

config.c

@@ -313,6 +313,12 @@ static enum parser_result parse_global_setting(const char *option,
 			return r;
 		*cfg->pi_offset_const = df;
 
+	} else if (!strcmp(option, "pi_f_offset_const")) {
+		r = get_ranged_double(value, &df, 0.0, DBL_MAX);
+		if (r != PARSED_OK)
+			return r;
+		*cfg->pi_f_offset_const = df;
+
 	} else if (!strcmp(option, "pi_max_frequency")) {
 		r = get_ranged_int(value, &val, 0, INT_MAX);
 		if (r != PARSED_OK)

config.h

@@ -76,6 +76,7 @@ struct config {
 	double *pi_proportional_const;
 	double *pi_integral_const;
 	double *pi_offset_const;
+	double *pi_f_offset_const;
 	int *pi_max_frequency;
 
 	unsigned char *ptp_dst_mac;

default.cfg

@@ -41,6 +41,7 @@ kernel_leap		1
 pi_proportional_const	0.0
 pi_integral_const	0.0
 pi_offset_const		0.0
+pi_f_offset_const	0.0000001
 pi_max_frequency	900000000
 clock_servo		pi
 #

gPTP.cfg

@@ -40,6 +40,7 @@ kernel_leap		1
 pi_proportional_const	0.0
 pi_integral_const	0.0
 pi_offset_const		0.0
+pi_f_offset_const	0.0000001
 pi_max_frequency	900000000
 clock_servo		pi
 #

ptp4l.8

@@ -268,9 +268,15 @@ The default is 0.0.
 .B pi_offset_const
 The maximum offset the PI controller will correct by changing the clock
 frequency instead of stepping the clock. When set to 0.0, the controller will
-never step the clock.
+never step the clock except on start.
 The default is 0.0.
 .TP
+.B pi_f_offset_const
+The maximum offset the PI controller will correct by changing the clock
+frequency instead of stepping the clock. This is only applied on the first
+update. When set to 0.0, the controller won't step the clock on start.
+The default is 0.0000001 (100 nanoseconds).
+.TP
 .B pi_max_frequency
 The maximum allowed frequency adjustment of the clock in parts per billion
 (ppb). This is an additional limit to the maximum allowed by the hardware. When

ptp4l.c

@@ -96,6 +96,7 @@ static struct config cfg_settings = {
 	.pi_proportional_const = &configured_pi_kp,
 	.pi_integral_const = &configured_pi_ki,
 	.pi_offset_const = &configured_pi_offset,
+	.pi_f_offset_const = &configured_pi_f_offset,
 	.pi_max_frequency = &configured_pi_max_freq,
 
 	.ptp_dst_mac = ptp_dst_mac,