1.\" $OpenBSD: udcf.4,v 1.25 2008/07/05 12:18:27 mbalmer Exp $ 2.\" 3.\" Copyright (c) 2006 - 2008 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: July 5 2008 $ 18.Dt UDCF 4 19.Os 20.Sh NAME 21.Nm udcf 22.Nd Gude ADS Expert mouseCLOCK USB timedelta sensor 23.Sh SYNOPSIS 24.Cd "udcf* at uhub?" 25.Sh DESCRIPTION 26The 27.Nm 28driver provides support for the Gude ADS Expert mouseCLOCK USB and 29the Expert mouseCLOCK USB II, receivers for the German DCF77 and the 30Swiss HBG time signal stations. 31While receivers for the British MSF time signal station are also 32being made, 33.Nm 34lacks support for them. 35.Pp 36.Nm 37implements a timedelta sensor and the delta (in nanoseconds) between the 38received time information and the local time can be accessed through the 39.Xr sysctl 8 40interface. 41The clock type is indicated in the sensor description: 42.Bl -tag -width "CRITICALXX" -offset indent 43.It DCF77 44German DCF77 time signal station 45(77.5 kHz longwave transmitter located in Mainflingen near Frankfurt). 46.It HBG 47Swiss HBG time signal station 48(75 kHz longwave transmitter located in Prangins near Geneva). 49.It Unknown 50The clock type has not been determined. 51.El 52.Pp 53The quality of the timedelta is reported as the sensor status: 54.Bl -tag -width "CRITICALXX" -offset indent 55.It UNKNOWN 56No valid time information has been received yet. 57.It OK 58The time information is valid and the timedelta is safe to use for 59applications like 60.Xr ntpd 8 . 61.It WARN 62The time information is still valid, but no new time information has been 63decoded for at least 5 minutes due to a reception or parity error. 64The timedelta should be used with care. 65.It CRITICAL 66No valid time information has been received for more than 15 minutes since 67the sensor state degraded from OK to WARN. 68This is an indication that hardware should be checked 69to see if it is still functional. 70The timedelta will eventually degrade to a lie 71as all computer internal clocks have a drift. 72.El 73.Sh SEE ALSO 74.Xr intro 4 , 75.Xr uhub 4 , 76.Xr usb 4 , 77.Xr ntpd 8 , 78.Xr sysctl 8 79.Sh HISTORY 80The 81.Nm 82driver first appeared in 83.Ox 4.0 . 84.Sh AUTHORS 85.An -nosplit 86The 87.Nm 88driver was written by 89.An Marc Balmer Aq mbalmer@openbsd.org . 90.Sh CAVEATS 91DCF77 uses a 77.5 kHz long wave radio signal transmitted from near Frankfurt, 92Germany. 93Up to about 900 km, the radio signal can travel directly to the receiver, 94providing a linearly increasing time offset based on distance. 95Due to the curvature of the Earth, beyond this distance the signal must 96bounce off the lower ionosphere (residing at approximately 70 km elevation 97during the day, and 90 km at night), thus causing a non-linearly increasing 98time offset which can only be roughly calculated using trigonometry. 99Since the distance and transmission geometry is not known, 100the clock receivers and 101.Nm 102driver currently make no effort to calculate this offset. 103We simply assume that the offset is small. 104.Pp 105In Germany, the train system uses DCF77 clocks. 106As the distance from Frankfurt increases, 107trains can be expected to run later. 108