Subject: Re: [PATCH] ptp: measure the time offset between PHC and system clock

From: Richard Cochran <[email-masked]>
Date: Sat, 14 Sep 2013 16:31:46 +0200

On Sat, Sep 14, 2013 at 04:03:06PM +0800, Dong Zhu wrote:
> This patch add a method into testptp.c to measure the time offset
> between phc and system clock through the ioctl PTP_SYS_OFFSET.
> 

This is a nice addition to the testptp program. I do have a few
comments, below.

First off, the subject line should mention testptp. How about this?

    [PATCH] ptp: add the PTP_SYS_OFFSET ioctl to the testptp program

> Signed-off-by: Dong Zhu <[email-masked]>
> ---
>  Documentation/ptp/testptp.c | 40 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/ptp/testptp.c b/Documentation/ptp/testptp.c
> index f59ded0..72bb030 100644
> --- a/Documentation/ptp/testptp.c
> +++ b/Documentation/ptp/testptp.c
> @@ -112,6 +112,7 @@ static void usage(char *progname)
>  		" -f val     adjust the ptp clock frequency by 'val' ppb\n"
>  		" -g         get the ptp clock time\n"
>  		" -h         prints this message\n"
> +		" -k val     measure the time offset between PHC and system clock\n"

The help message should tell the user what 'val' is.

>  		" -p val     enable output with a period of 'val' nanoseconds\n"
>  		" -P val     enable or disable (val=1|0) the system clock PPS\n"
>  		" -s         set the ptp clock time from the system time\n"
> @@ -133,8 +134,12 @@ int main(int argc, char *argv[])
>  	struct itimerspec timeout;
>  	struct sigevent sigevent;
>  
> +	struct ptp_clock_time *pct;
> +	struct ptp_sys_offset *sysoff;
> +
> +
>  	char *progname;
> -	int c, cnt, fd;
> +	int i, c, cnt, fd;
>  
>  	char *device = DEVICE;
>  	clockid_t clkid;
> @@ -144,6 +149,8 @@ int main(int argc, char *argv[])
>  	int extts = 0;
>  	int gettime = 0;
>  	int oneshot = 0;
> +	int offset = 0;
> +	int n_samples = 0;
>  	int periodic = 0;
>  	int perout = -1;
>  	int pps = -1;
> @@ -151,7 +158,7 @@ int main(int argc, char *argv[])
>  
>  	progname = strrchr(argv[0], '/');
>  	progname = progname ? 1+progname : argv[0];
> -	while (EOF != (c = getopt(argc, argv, "a:A:cd:e:f:ghp:P:sSt:v"))) {
> +	while (EOF != (c = getopt(argc, argv, "a:A:cd:e:f:ghk:p:P:sSt:v"))) {
>  		switch (c) {
>  		case 'a':
>  			oneshot = atoi(optarg);
> @@ -174,6 +181,10 @@ int main(int argc, char *argv[])
>  		case 'g':
>  			gettime = 1;
>  			break;
> +		case 'k':
> +			offset = 1;
> +			n_samples = atoi(optarg);
> +			break;
>  		case 'p':
>  			perout = atoi(optarg);
>  			break;
> @@ -376,6 +387,31 @@ int main(int argc, char *argv[])
>  		}
>  	}
>  
> +	if (offset) {
> +		sysoff = calloc(1, sizeof(*sysoff));
> +		if (!sysoff) {
> +			perror("calloc");
> +			return -1;
> +		}
> +		sysoff->n_samples = n_samples;
> +
> +		if (ioctl(fd, PTP_SYS_OFFSET, sysoff))
> +			perror("PTP_SYS_OFFSET");
> +		else
> +			puts("time offset between PHC and
> +					 system clock request okay");
> +
> +		pct = &sysoff->ts[0];
> +		for (i = 0; i < sysoff->n_samples; i++, pct++) {
> +			printf("system time: %ld.%ld\n", pct->sec, pct->nsec);
> +			pct++;
> +			printf("phc    time: %ld.%ld\n\n", pct->sec, pct->nsec);
                                                    ^^^^
I think the output would look nicer with only one newline. After all,
each measurement is a {sys,phc,sys} triplet and not a {sys,phc} pair.

> +		}
> +		printf("system time: %ld.%ld\n", pct->sec, pct->nsec);
> +
> +		free(sysoff);
> +	}
> +

Thanks,
Richard