NAME
udcf —
Gude ADS Expert mouseCLOCK USB
timedelta sensor
SYNOPSIS
udcf* at uhub?
DESCRIPTION
The udcf driver provides support for the
Gude ADS Expert mouseCLOCK USB and the Expert mouseCLOCK USB II, receivers
for the German DCF77. While receivers for the British MSF time signal
station are also being made, udcf lacks support for
them.
udcf implements a timedelta sensor and the
delta (in nanoseconds) between the received time information and the local
time can be accessed through the
sysctl(8) interface. The clock type is indicated in the sensor
description:
- DCF77
- German DCF77 time signal station (77.5 kHz longwave transmitter located in Mainflingen near Frankfurt).
The quality of the timedelta is reported as the sensor status:
- UNKNOWN
- No valid time information has been received yet.
- OK
- The time information is valid and the timedelta is safe to use for applications like ntpd(8).
- WARN
- The time information is still valid, but no new time information has been decoded for at least 5 minutes due to a reception or parity error. The timedelta should be used with care.
- CRITICAL
- No valid time information has been received for more than 15 minutes since the sensor state degraded from OK to WARN. This is an indication that hardware should be checked to see if it is still functional. The timedelta will eventually degrade to a lie as all computer internal clocks have a drift.
SEE ALSO
HISTORY
The udcf driver first appeared in
OpenBSD 4.0.
AUTHORS
The udcf driver was written by
Marc Balmer
<mbalmer@openbsd.org>.
CAVEATS
DCF77 uses a 77.5 kHz long wave radio signal transmitted from near
Frankfurt, Germany. Up to about 900 km, the radio signal can travel directly
to the receiver, providing a linearly increasing time offset based on
distance. Due to the curvature of the Earth, beyond this distance the signal
must bounce off the lower ionosphere (residing at approximately 70 km
elevation during the day, and 90 km at night), thus causing a non-linearly
increasing time offset which can only be roughly calculated using
trigonometry. Since the distance and transmission geometry is not known, the
clock receivers and udcf driver currently make no
effort to calculate this offset. We simply assume that the offset is
small.
In Germany, the train system uses DCF77 clocks. As the distance from Frankfurt increases, trains can be expected to run later.