Address: 127.127.7.u
Reference ID: CHU
Driver ID: CHU
Serial Port: /dev/chuu; 300 baud, 8-bits, no
parity
Features: chu_clk
This driver supports a shortwave receiver and special modem circuitry
described in the ./gadget directory of the xntp3 distribution. It
requires the chu_clk line discipline or streams module
described in the Line Disciplines and Streams
Drivers page. It also requires a gadget box and 300-bps modem, such
as described in the Pulse-per-second (PPS) Signal
Interfacing page.
Unlike the NIST time services, whose timecode requires quite specialized hardware to interpret, the CHU timecode can be received directly via a serial port after demodulation. While there are currently no known commercial CHU receivers, the hardware required to receive the CHU timecode is fairly simple to build. While it is possible to configure several CHU units simultaneously, this is in general not useful.
The time1 fudge option can be used to set the CHU
propagation delay, compensate for inherent latencies in the serial port
hardware and operating system. The default value is 0.0025 seconds,
which is about right for Toronto. Values for other locations can be
calculated using the propdelay program in the util directory of the
xntp3 distribution or equivalent means.
The time2 fudge option can also be used to compensate
for inherent latencies in the serial port hardware and operating system.
The value, which defaults to zero, is in addition to the propagation
delay provided by the time1 option. The default value is 0.0002 seconds,
which is about right for typical telephone modem chips.
The flag1 option can be used to modify the averaging
algorithm used to smooth the clock indications. Ordinarily, the
algorithm picks the median of a set of samples, which is appropriate
under conditions of poor to fair radio propagation conditions. If the
clock is located relatively close to the WWV or WWVH transmitters,
setting this flag will cause the algorithm to average the set of
samples, which can reduce the residual jitter and improve accuracy.
When enabled by the flag4 fudge flag, every received
timecode is written as-is to the clockstats file.
time1 time
time2 time
stratum number
refid string
CHU.
flag1 0 | 1
flag2 0 | 1
flag3 0 | 1
flag4 0 | 1
clockstats recording if set.