doc: update FAQ on improving accuracy

diff --git a/doc/faq.adoc b/doc/faq.adoc
index 32210c74edde8b4e547d18cb6361511619a862e2..06eaabcda4920855c85d662e8ca40eadaeee2433 100644 (file)
--- a/doc/faq.adoc
+++ b/doc/faq.adoc
@@ -381,7 +381,7 @@ outliers corrupting the minimum delay. For example:
 server ntp.local minpoll -7 maxpoll -7 filter 31 maxdelayquant 0.3 xleave
 ----
 
-As an experimental feature added in version 4.2, `chronyd` supports an NTPv4
+Since 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:
@@ -390,6 +390,18 @@ the `extfield F323` option. For example:
 server ntp.local minpoll 0 maxpoll 0 xleave extfield F323
 ----
 
+Since version 4.5, `chronyd` can apply corrections from PTP one-step end-to-end
+transparent clocks (e.g. network switches) to significantly improve accuracy of
+synchronisation in local networks. It requires the PTP transport to be enabled
+by the `ptpport` directive, HW timestamping, and the `extfield F324` option.
+For example:
+
+----
+server ntp.local minpoll -4 maxpoll -4 xleave extfield F323 extfield F324 port 319
+ptpport 319
+hwtimestamp eth0 minpoll -4
+----
+
 === Does `chronyd` have an ntpdate mode?
 
 Yes. With the `-q` option `chronyd` will set the system clock once and exit.