GPS Time Standard and Linux NTP
This is a follow-up topic to the NTP thread of a couple weeks ago... for those of you who may be interested in accessing GPS as a time standard for your local Suse NTP server, as an alternative to using one of the primary or secondary external NTP servers. Often folks forget about the GPS alternative. I have been playing with the Earthmate GPS LT-20 by DeLorme (carried by BestBuy and others lately). This GPS unit is nicely compatible with Linux (specifically gpsdrive, and gpsd; both ship with Suse 10) as well as minicom or other serial terminal emulator. The device does not require M$ software, nor does it require proprietary drivers. The device is quite small 6.7cm x 4.5 cm x 1.5 cm, and comes complete with an attached 1.5 m USB cable. The LT-20 is USB powered, self-contained, and communicates outbound over USB using the NMEA ascii standard sentences. These sentences may be parsed by a simple script, or extracted via gpsd via telnet. The LT-20 uses a twelve channel RF receiver chip from SiGE (SE4100L) and the GPS micro controller chip from ST Microelectronics (STA2051). Operation is simple... plug it into an available USB port on your local Suse box and go... The NMEA output sentences can be accessed via minicom at 4800 baud N81 to device /dev/ttyUSBx (where x will be 0 for the first device). Otherwise gpsd can be started after plugging in the unit: gpsd -p /dev/ttyUSB0 By default gpsd uses port 2947. Accessing the NMEA output is as simple as running telnet to port 2947 and pressing the 'R' command to receive 'raw' data. telnet localhost 2947 ... the date and time can be extracted with the 'D' command. Obviously the beauty of the GPS receiver is to be able to provide global positioning for navigation, orienteering, etc... but often computer folks forget that the GPS system is an excellent time standard for a local NTP server, or other time coordination scheme. The myth is that GPS time can not be relied upon because of a leap second snafu. This is not true, however. The failure of GPS time has been in the firmware on GPS receivers (programming errors) not the GPS system, software, or clocks. Fortunately the LT-20 handles the time correctly. Consequently, the LT-20 can be used with your Suse linux system as a reliable time standard for your local server without the need for accessing external NTP servers. -- Kind regards, M Harris <><
M Harris wrote:
This is a follow-up topic to the NTP thread of a couple weeks ago... for those of you who may be interested in accessing GPS as a time standard for your local Suse NTP server, as an alternative to using one of the primary or secondary external NTP servers. Often folks forget about the GPS alternative.
I think the reason is that GPS receivers with the proper interfaces available are usually in a very different price class to DCF77 (Germany), Kalundborg (Denmark), MSF Rugby (UK) or HBG (Switzerland) longwave receivers. Some of these can be built for a few euros, especially if you've got a soldering iron and the basic parts. Per Jessen, Zurich -- http://www.spamchek.com/ - managed email security. Starting at SFr5/month/user.
participants (2)
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M Harris
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Per Jessen