1.\" $OpenBSD: nmea.4,v 1.22 2008/05/06 09:01:08 mbalmer Exp $ 2.\" 3.\" Copyright (c) 2006, 2007 Marc Balmer <mbalmer@openbsd.org> 4.\" 5.\" Permission to use, copy, modify, and distribute this software for any 6.\" purpose with or without fee is hereby granted, provided that the above 7.\" copyright notice and this permission notice appear in all copies. 8.\" 9.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16.\" 17.Dd $Mdocdate: May 6 2008 $ 18.Dt NMEA 4 19.Os 20.Sh NAME 21.Nm nmea 22.Nd NMEA 0183 timedelta sensor 23.Sh SYNOPSIS 24.Cd "pseudo-device nmea" Op Ar count 25.Sh DESCRIPTION 26This line discipline interfaces NMEA devices, 27such as GPS receivers attached to a serial or USB port. 28.Pp 29The line discipline is enabled by the following sequence: 30.Bd -literal -offset indent 31#include <sys/ttycom.h> 32int ldisc = NMEADISC, fildes; ... 33ioctl(fildes, TIOCSETD, &ldisc); 34.Ed 35.Pp 36The byte stream is unaltered by the line discipline which 37maintains a timedelta sensor using the NMEA data. 38The timedelta sensor will appear as nmea* in the list of sensors and the delta 39(in nanoseconds) between the received time information and the local time can 40be accessed through the 41.Xr sysctl 8 42interface. 43.Sh NMEA SENTENCES 44The 45.Nm 46line discipline decodes the following NMEA 0183 sentences: 47.Bl -tag -width "GPRMCXX" 48.It GPRMC 49Recommended Minimum Specific GPS/TRANSIT Data. 50Only the time and date information is extracted. 51The warning indication is used to provide the sensor status (see below). 52If the attached device sends the GPRMC message in the 13-field format, 53the operation mode of the GPS device is reported in the sensor description. 54The sensor timestamp is copied from the tty timestamp if a device with PPS 55is being used and tty timestamping has been turned on. 56Otherwise the sensor timestamp is taken when the initial `$' character of 57a message block is received from the NMEA device. 58.El 59.Sh SENSOR STATES 60The quality of the timedelta is reported as the sensor status: 61.Bl -tag -width "CRITICALXX" -offset indent 62.It OK 63The time information is valid. 64The timedelta is safe to use for applications like 65.Xr ntpd 8 . 66.It WARN 67The attached GPS receiver has been indicating a warning condition 68for at least the last ten minutes. 69The timedelta should be used with care. 70.It CRITICAL 71tty timestamping has been turned on but there is no PPS signal present or the 72GPS receiver indicated a warning condition for at least the last twenty 73minutes. 74Check your hardware. 75Some GPS units need PPS to be manually turned on. 76.El 77.Pp 78The status of a second sensor is used to report the status of the 79device itself: 80.Bl -tag -width "CRITICALXX" -offset indent 81.It OK 82The clock is synchronized, e.g. a GPS receiver has a fix. 83.It WARN 84The device issued a warning condition, e.g. a GPS receiver has no fix. 85.El 86.Sh SEE ALSO 87.Xr tty 4 , 88.Xr ldattach 8 , 89.Xr ntpd 8 , 90.Xr sysctl 8 91.Sh HISTORY 92The 93.Nm 94interface first appeared in 95.Ox 4.0 . 96.Sh AUTHORS 97The 98.Nm 99line discipline was written by 100.An Marc Balmer Aq mbalmer@openbsd.org . 101