🚀 go-pugleaf

Well, here's a comment out of the module of ntpd for unix.  It seems that
while you can get time samples from the clock, which one do you believe?

Other clocks, like the Spectracom 8170 WWVB clock, provide a seperate
TTL level output which is the on-time pulse.  It is driven high for 100 ms,
with the leading edge of the pulse corresponding to the beginning of the
second.

/* read_clock_heath() -- Read the Heath Radio Clock.
 *
 * Strategy Notes:
 *
 * When the heath clock is set at 9600 baud and is in continuous mode,
 * it will output an alternating set of two or three time strings per tenth
 * of a second.  For instance:
 *
 * 22:20:04.2     07/26/89<CR>
 * 22:20:04.2     07/26/89<CR>
 * 22:20:04.3     07/26/89<CR>
 * 22:20:04.3     07/26/89<CR>
 * 22:20:04.3     07/26/89<CR>
 * 22:20:04.4     07/26/89<CR>
 * 22:20:04.4     07/26/89<CR>
 * 22:20:04.5     07/26/89<CR>
 * 22:20:04.5     07/26/89<CR>
 * 22:20:04.5     07/26/89<CR>
 *
 * We assume that the best place to take a time sample is at the start of
 * the first string of a 3 string sequence.  This is based solely on the
 * guess that fitting 3 strings in 1/10th of a second means that the first
 * string is closer to "on-time" than if just two strings fit.
 */

Some other people have asked about sources of WWV/WWVB synchronized and other
reference clocks.  Here's a list of clocks and their sources:


Radio timecode receivers and other sources of synchronization

Following is a list of radio timecode receivers currently on the market.
These devices are attached via a serial asynchronous line, which is used to
send poll messages and receive responses in the following example formats:

Spectracom clock: <cr><lf>q  ddd hh:mm:ss  tz=zz<cr>    (22 chars)
Truetime clock:   <cr><lf><ctrl-a>ddd:hh:mm:ssq<cr>     (13 chars)
Heath clock:      <cr>hh:mm:ss.f     dd/mm/yr<cr>       (23 chars)
PST clock:        hh:mm:ss.fff  yy/dd/mm/ddd status<cr> (49 chars)

These formats are exhibited for example only. In some clocks an extensive
repitoire of commands and formats are available.

In the Fuzzball implementation the Spectracom and PST clocks are polled,
which return the time-code string shown, while the other clocks run
continuously. In the Truetime clock the start bit of the last <cr>
represents on-time, while in the other clocks the first <cr> represents on-
time. In the time code ddd is day of year, hh:mm:ss is time of day, f is
fractions of seconds, and dd/mm/yr is conventional (US) date. In the
Spectracom clock, q is " " for in-synch or "?" for off-synch and zz is the
time zone (always 00 for UT). In the Truetime clock, q is a precision
estimate in milliseconds and coded as follows: "?" +-500 msec, "#" +-50
msec, "*" +-5 msec, "." +-1 msec, <sp> less than 1 msec. In the Heath clock,
the hh:mm:ss.f field is displayed as 0?:??:??.? before synch is first
established and hh:mm:ss.? once synch is established and then lost again.

Model 8170 WWVB Synchronized Clock ($2500)
Spectracom Corporation
101 Despatch Drive
East Rochester, NY 14445
(716) 381-4827

     This is a LF receiver and decoder for the WWVB station. It is supported
     in the Fuzzball operating system. For expected accuracies less than 10
     ms, a special one-second on-time signal produced by the clock must be
     used to fine-tune the indication.

Model 468-DC Satellite Synchronized Clock ($4500)
True Time Division, Kinemetrics
3243 Santa Rosa Avenue, Santa Rosa, CA 95401
(707) 528-1230

     This is a UHF receiver and decoder for the GOES satellite. It is
     supported in the Fuzzball operating system.

Model 1020 Integrated Time Source ($1500)
Precision Standard Time, Inc.
105 Fourier Avenue, Fremont, CA 94539
(415) 656-4447

     This is an HF receiver and decoder for the WWV/WWVH stations. A Unix
     driver is included in the NTP daemon ntpd; however, Version 4.01 of the
     clock firmware is required. It is supported in the Fuzzball operating
     system. This receiver is now being marketed by the Traconex
     Corporation.

Model GC-1000 Most Accurate Clock ($300)
Heath Company
Benton Harbor, MI 49022
(616) 982-3411

     This is an HF receiver and decoder for the WWV/WWVH stations. It is
     supported in the Fuzzball operating system.

8101 Automated Computer Time Service (ACTS)
Time and Frequency Division, National Bureau of Standards
US Department of Commerce, Gaithersburg, MD 20899

     This is a package of C software for the IBM Personal Computer. It can
     be used to call a special NBS number using either 300-Hz or 1200-Hz
     modem and set the computer clock. The latest version has been adapted
     to run on Unix workstations.

Model ? MSF Synchronized Clock ($?)
European Electric Systems, Ltd.
Woodham Mortimer Place, Rectory Lane
Woodham Mortimer, Maldon, Essex. CM9 6SW, United Kingdom
+44 24541 5785, (FAX) +44 24541 5785

     This is a LF receiver for the MSF (Rugby, UK) station. It is reported
     they manufacture a US version for the WWVB station.
     
Model 5061A/B Cesium Clock ($40,000)
Hewlett Packard, Co., Customer Information Center
19310 Pruneridge Avenue, 49A
Cupertino, CA 95014

     This is a cesium-stabilized oscillator which produces various outputs,
     including a 1 pulse-per-second output which can be used to stabilize
     frequency and provide accurate time when used in conjunction with a
     radio clock. It is supported in the Fuzzball operating system.