Re: [Linuxptp-users] sanity_freq_limit

[Daniel Le <dan...@ex...>]

> On Jun 18, 2015, at 2:58 AM, Miroslav Lichvar <mli...@re...> wrote:
> 
>> On Thu, Jun 18, 2015 at 01:58:13AM +0000, Daniel Le wrote:
>> Additionally, in slave clock operation and software time stamping mode, how (and where in the code) ptp4l can be forced to step the system clock with the time it first receives from a grandmaster clock?
> 
> ptp4l should do that by default, it's set by the first_step_threshold
> option.

Somehow when my system clock is initially (for example after a reboot) off the GM time by a couple of minutes, the master offset is huge and ptp4l takes hours to converge.

Thanks.

> 
>> I have a couple of questions about the frequency limit. How much may it be reasonably increased from the default of 200000000 (20%)? And this parameter is only configurable via the config file. Is that correct?
> 
> Why do you need to increase it? 20% is a safe value for SW
> timestamping. If you see clockcheck warning messages, it's probably a
> bug in the kernel/driver. With HW timestamping a limit of a few
> hundreds of ppm should be enough to cover the frequency offset between
> a typical system clock and PTP clock.
> 
> -- 
> Miroslav Lichvar