GPSD Overview<\/h3>\n
GPSD is the server that monitors the GNSS\/GPS (if included with your device) and makes time and position information available to client programs, such as gpsmon and NTPD.\u00a0 GPSD communicates with NTPD via shared memory to provide the GPS time. \u00a0The server allows multiple programs to use the GNSS\/GPS. \u00a0It also detects leap second and tells NTPD of an upcoming leap second and its direction on the day of the leap second.<\/p>\n
The script\u00a0\/usr\/sbin\/gpsd_fixed<\/strong>\u00a0has no parameters, but uses the file\u00a0\/etc\/default\/gpsd <\/strong>which\u00a0contains\u00a0the\u00a0parameter,\u00a0GPSFIX,<\/strong>\u00a0as a criteria to determine if the GNSS\/GPS currently has a fix (lock) on the satellites. If there is a fix, it creates a file\u00a0\/var\/run\/gpsfix<\/strong>, with the contents equal to the actual GPS fix value found. Otherwise the file is deleted.\u00a0The script\u00a0\/usr\/sbin\/gpsd_settime<\/strong>\u00a0checks for a GPS fix. If so, it sets the system clock to the GPS time, first using the GNSS\/GPS, in case there is a huge change, then using\u00a0ntpd -gq<\/strong>\u00a0to get it much closer.<\/p>\n NTP\/NTPD ultimately manages the time based reliability and availability of time sources (with top priority going to the GPS time).\u00a0For more information on NTPD and how it manages time, see the\u00a0NTPD<\/a>\u00a0page.<\/p>\n Here are the key files for setup of the GPSD on the device:<\/p>\n GPSD configuration file<\/b><\/span><\/p>\n Here is the default configuration file, \/etc\/default\/gpsd:<\/p>\n The GPSD program uses the uBlox proprietary binary message mode to communicate with the GPS as the most efficient method.<\/p>\n Here are the major elements of the GPSD<\/b> configuration file:.<\/p>\n gpsmon utility<\/b><\/span><\/p>\n The GNSS\/GPS output may be observed using the gpsmon utility<\/b>. gpsmon <\/b>works best using ssh and ethernet with the device.<\/p>\n To run the utility, enter the following command:<\/p>\n The resulting output displays:<\/p>\n Notice the box with the label NAV_SOL<\/b> <\/i>at the bottom. In this box, the bottom line is Fix 0x03<\/b>. This is one of the acceptable values mentioned in \/etc\/default\/gpsd for GPSFIX.<\/p>\n With the value of GPSFIX set to 03 05<\/b> in the configuration file, either 0x03<\/b> or 0x05<\/b> is acceptable in the gpsmon<\/b> output.<\/p>\n Bash script to check GNSS\/GPS status<\/b><\/span><\/p>\n This bash script<\/b> is located in\u00a0 \/usr\/sbin\/gpsd_fixed <\/b>on the device. It uses the utility, gpsmon,<\/b> to determine when the GPS fix field<\/b> in the UBX NAV SOL message<\/b> indicates a fix matching one of the fixes of the GPSFIX variables<\/b> specified in the configuration file (\/etc\/default\/gpsd<\/b>). The fix choices in the GPSFIX variable<\/b> are space separated and the values are in hex, but no value over 05<\/b> is allowed.<\/p>\n Here is how the bash script<\/b> works:<\/p>\n 1. To execute the b<\/strong>ash script<\/b>, enter the command:<\/p>\n 2. The script returns an exit status of 0 <\/b>if one of the fixes specified is achieved.<\/p>\n 3. One of the following occurs next:<\/p>\n a. If the script executes and one of the GPSFIX values<\/b> is achieved, the GPS fix field valu<\/b>e is placed in the file GPS_FIXFILE<\/b>, as specified in \/etc\/default\/gpsd<\/b>.<\/p>\n OR<\/strong><\/p>\n b. If the fix value<\/b> is not one of the values specified in GPSFIX<\/b>, the file GPS_FIXFILE<\/b> is removed. The GPS is not ready yet. Wait and try again.<\/p>\n 4. From powerup, it takes six to ten minutes before the GPS fix<\/b> reaches 0x03<\/b>, which is a 3D fix<\/b>.<\/p>\n Bash script to set the system clock <\/b><\/span><\/p>\n This bash script sets the system clock using gpsmon output <\/b>if \/usr\/sbin\/gpsd_fixed<\/b> indicates the GPS fix<\/b>.<\/p>\n To execute this script, enter the following:<\/p>\n This is needed prior to starting NTPD<\/b> to prevent the GPS<\/b> from being marked as a falseticker.<\/p>\n Using gpsd with the gpsd python library<\/b><\/span><\/p>\n The gpsd python library is contained in the following package:<\/p>\n python-pygps<\/p>\n This library is provided on the mLinux image, and from the Downloads page, the item named Pre-built Packages.<\/p>\n Using the library in a python script will require the following import statement:<\/p>\n from gps import *<\/p>\n You can download an example here:<\/p>\n\n
ENABLED=\"yes\"\r\nGPSD_SOCKET=\"\/var\/run\/gpsd.sock\"\r\nGPSD_OPTIONS=\"-n -D 1\"\r\n\r\n# Conduit 0.1 GPS devices\r\nGPS_LINE=\/dev\/ttyXRUSB2\r\n\r\n# Highest speed permitted by uBlox.\r\nGPS_BAUD=115200\r\nGPS_DEVICES=\"$GPS_LINE \/dev\/pps0\"\r\n\r\nGPS_FIXFILE=\/var\/run\/gpsfix\r\n\r\n# GPSD\/UBlox Lock requirement\r\n# Create GPS_FIXFILE when reached.# UBlox NAV SOL (0x01 0x06) at gpsFix value\r\n# and above\r\n# 00 No Fix\r\n# 01 Dead reckoning only\r\n# 02 2D fix\r\n# 03 3D fix\r\n# 04 GPS + dead reckoning combined\r\n# 05 Time only fix\r\nGPSFIX=\"03 05\"<\/pre>\n
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mtcdt: gpsmon<\/pre>\n
![\"\"](\"https:\/\/www.multitech.net\/developer\/wp-content\/uploads\/2017\/01\/gpsmon-utility-output.png\")
<\/p>\nmtcdt: \/usr\/sbin\/gpsd_fixed<\/pre>\n
mtcdt:\/usr\/sbin\/gpsd_settime<\/pre>\n