Re: [Linuxptp-devel] [PATCH v1] phc_ctl: Implement setting frequency from system time.

[Richard C. <ric...@gm...>]

On Wed, Sep 13, 2023 at 05:09:04PM +0000, Maciek Machnikowski wrote:
> Implement auto mode for frequency setting. In this mode the tool
> will measure the frequency difference between PHC and CLOCK_REALTIME
> and apply the correction to the PHC to match the system clock.

...

> +		/* Try sysoff first */
> +		method = sysoff_probe(fd, N_SAMPLES);
> +		if (method >= 0) {
> +			if (sysoff_measure(fd, method, N_SAMPLES,
> +					   &t1_sys_offset,
> +					   &t1_sys_ts, &t1_delay)) {
> +				return -1;
> +			}
> +
> +			sleep(1);

This measurement interval is WAY too short.  The time stamp error will
spoil the syntonization.
 
> +			if (sysoff_measure(fd, method, N_SAMPLES,
> +					   &t2_sys_offset,
> +					   &t2_sys_ts, &t2_delay)) {
> +				return -1;
> +		       }
> +
> +			sys_diff = t2_sys_ts - t1_sys_ts;
> +			clk_diff = t2_sys_offset - t1_sys_offset;
> +			ppb += (1e9 - ppb) * ((double)clk_diff / (double)sys_diff);

Thanks,
Richard