diff options
author | Eric S. Raymond <esr@thyrsus.com> | 2013-10-20 21:21:33 -0400 |
---|---|---|
committer | Eric S. Raymond <esr@thyrsus.com> | 2013-10-20 21:21:33 -0400 |
commit | d5bbb5285781c2fe36d6c219d3e738229d36ead2 (patch) | |
tree | 88f8c20fd706f2e6d51bbdd32da48d494073fc6b /www | |
parent | 809a7c3badbad2229bfdcf5716fc00bc60c49cf2 (diff) | |
download | gpsd-d5bbb5285781c2fe36d6c219d3e738229d36ead2.tar.gz |
HOWTO polishing by HÃ¥kan Johansson <f96hajo@chalmers.se>.
Diffstat (limited to 'www')
-rw-r--r-- | www/gpsd-time-service-howto.txt | 24 |
1 files changed, 12 insertions, 12 deletions
diff --git a/www/gpsd-time-service-howto.txt b/www/gpsd-time-service-howto.txt index 852d1342..5dbc4fa1 100644 --- a/www/gpsd-time-service-howto.txt +++ b/www/gpsd-time-service-howto.txt @@ -7,9 +7,9 @@ you can find the original at the GPSD project website. == Introduction == -GPSD, NTP and a GPS supplying 1PPS output can be used to set up a -high-quality NTP time server. This HOWTO explains the method and -various options you have in setting it up. +GPSD, NTP and a GPS supplying 1PPS (pulse-per-second) output can be +used to set up a high-quality NTP time server. This HOWTO explains the +method and various options you have in setting it up. The document you see is a draft in progress. We would like to produce a comprehensive guide suitable for people who know little about time @@ -91,16 +91,16 @@ pulse delivered by some GPSes to correct a local NTP instance. GPS satellites deliver a top-of-GPS-second notification that is nominally accurate to 50nSec. 1PPS-capable GPSes often use an RS-232 -control line to ship the 1PPS edge of second to the host system (usually -Carrier Detect or Ring Indicator; GPSD will quietly accept either). -Satellite top-of-second loses some accuracy on the way down due mainly -to variable delays in the ionophere; processing overhead in the GPS -itself adds a bit more latency, and your server detecting that pulse add -still more latency. But it's still often accurate to on the order of 1 -uSec. +control line to ship the 1PPS edge of second to the host system +(usually Carrier Detect or Ring Indicator; GPSD will quietly accept +either). Satellite top-of-second loses some accuracy on the way down +due mainly to variable delays in the ionosphere; processing overhead +in the GPS itself adds a bit more latency, and your server detecting +that pulse add still more latency and jitter. But it's still often +accurate to on the order of 1 uSec. Under most Unixes there are two ways to watch 1PPS; Kernel PPS (KPPS) -and plain PPS. KPPS is formally known as RFC 2783 PPS. These have +and plain PPS latching. KPPS is formally known as RFC 2783 PPS. These have different error budgets. Kernel PPS uses a kernel function to accurately timestamp the status @@ -356,7 +356,7 @@ $ su - chrony is an alternative open-source implementation of NTP service, originally designed for systems with low-bandwidth or intermittent -TCP/IP service. It interoperates with ntpd using the same protocols, +TCP/IP service. It interoperates with gpsd using the same protocols, but is somewhat easier to configure and administer. The chrony project has a home page at <<CHRONY>>. |