Gude ADS Expert mouseCLOCK USB timedelta sensor
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
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:
- 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:
- No valid time information has been received yet.
- The time information is valid and the timedelta is safe to use for
applications like ntpd(8).
- 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.
- 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
udcf driver first appeared in
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.