UDCF(4) | Device Drivers Manual | UDCF(4) |
udcf
— Gude ADS
Expert mouseCLOCK USB timedelta sensor
udcf* at uhub?
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:
The quality of the timedelta is reported as the sensor status:
The udcf
driver first appeared in
OpenBSD 4.0.
The udcf
driver was written by
Marc Balmer
<mbalmer@openbsd.org>.
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.
June 7, 2015 | OpenBSD-6.8 |