PPS code is now part of the main line.

1 files changed, 11 insertions, 2 deletions

diff --git a/gpsd.xml b/gpsd.xml
index 088969ee..d39709e9 100644
--- a/gpsd.xml
+++ b/gpsd.xml
@@ -588,12 +588,21 @@ updates.</para>
 
 <para>gpsd can provide reference clock information to
 <application>ntpd</application>, to keep the system clock synchronized
-to the time provided by the GPS receiver.</para>
+to the time provided by the GPS receiver.  Note that if you're going
+to use <application>gpsd</application> you probably want to run it
+<option>-n</option> mode so the clock will be updated ebven when no
+clients are active.</para>
 
 <para>Note that deriving time from messages received from the GPS
 receiver is not as accurate as you might expect.  Messages are often
 delayed in the receiver and on the link by several hundred
-milliseconds, and this delay is not constant.</para>
+milliseconds, and this delay is not constant.  On Linux,
+<application>gpsd</application> includes support for interpreting the
+PPS pulses emitted at the start of every clock second on the
+carrier-detect lines of some serial GPSes; this pulse is used to
+update NTP at much higher precision.  You can determine whethher
+your GPS emits this pulse by running at -D 5 and watching for 
+carrier-detect state change messages in the logfile.</para>
 
 <para>When <application>gpsd</application> receives a sentence with a
 timestamp, it packages the received timestamp with current local time