From 17e6258694e0b612bc59851c5a289631a869b0ac Mon Sep 17 00:00:00 2001 From: Miroslav Lichvar Date: Tue, 23 Nov 2021 16:05:16 +0100 Subject: [PATCH] doc: update FAQ --- doc/faq.adoc | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/doc/faq.adoc b/doc/faq.adoc index 80853b4..d1b4cf3 100644 --- a/doc/faq.adoc +++ b/doc/faq.adoc @@ -345,6 +345,15 @@ server ntp.local minpoll -6 maxpoll -6 filter 15 xleave hwtimestamp eth0 minpoll -6 ---- +As an experimental feature added in version 4.2, `chronyd` supports an NTPv4 +extension field containing an additional timestamp to enable frequency transfer +and significantly improve stability of synchronisation. It can be enabled by +the `extfield F323` option. For example: + +---- +server ntp.local minpoll 0 maxpoll 0 xleave extfield F323 +---- + === Does `chronyd` have an ntpdate mode? Yes. With the `-q` option `chronyd` will set the system clock once and exit. @@ -468,7 +477,8 @@ leap seconds from other sources (e.g. with the `leapsectz` directive in === Does `chrony` support PTP? -No, the Precision Time Protocol (PTP) is not supported and there are no plans +No, the Precision Time Protocol (PTP) is not supported as a protocol for +synchronisation of clocks and there are no plans to support it. It is a complex protocol, which shares some issues with the NTP broadcast mode. One of the main differences between NTP and PTP is that PTP was designed to be easily supported in hardware (e.g. network switches and @@ -483,6 +493,11 @@ packets (enabled by the `hwtimestamp` directive) if the NIC can timestamp other packets than PTP, which is usually the case at least for transmitted packets. The `ethtool -T` command can be used to verify the timestamping support. +As an experimental feature added in version 4.2, `chrony` can use PTP as a +transport for NTP messages (NTP over PTP) to enable hardware timestamping on +hardware which can timestamp PTP packets only. It can be enabled by the +`ptpport` directive. + === What happened to the `commandkey` and `generatecommandkey` directives? They were removed in version 2.2. Authentication is no longer supported in the