On Wed, 3 Aug 2011 08:36:21 +0200, Rob van der Heij <rvdh...@gmail.com> w rote:
>On Tue, Aug 2, 2011 at 8:54 PM, David Boyes <dbo...@sinenomine.net> wrot e: > >> How come Z hardware doesn't come with one of these? 8-) > >Because the machines are mostly installed in places where you don't >have sufficiently open sky to receive GPS... Similar concerns >prevented usage of the radio beacons that feed consumer grade >automatic clocks. And you probably experienced once in a while that >your navigation system was off by far... you would need to harden the >signal seriously. It's amazing how complicated it gets when you want >to make it reliable enough to hook up to the mainframe. I actually used a 25-foot extension of CAT-3 cable to the 18-foot factory installed cable when I made mine because I was anticipating the need to potentially mount it outdoors. Turned out that was needless. It receive s quite well in my conventional wood frame house without a view of the sky while sitting atop my desk. More cable would be feasible. (Others have u sed a skylight and put the puck in the skylight.) It only needs five volts th us the beauty and simplicity of using USB for power only. If the cable was s o long that voltage drop off happened, then I'm sure that could be easily overcome. Sure, some mainframe systems are located in, umm, certain dee p underground facilities in the western USA. I think that "mostly installed in places" that cannot receive GPS is too harsh. I visited TONS of customer shops with windows or top floor machine rooms in my career. The bunker installs are not the only world of installed mainframes. ;-) Because the GPS in this usage is a stationary receiver (I do not drive my desk around the house like Conan O'brien does with his on his tv show), t he navigation fix is constant unless experiencing an earthquake. The navigation fix provided by the satellites allow the time to be determined and delivered, and *that* further allow the GPS to deliver the pulse-per-second signal because it knows when the second boundary crosses . GPSD gets the signal through the serial cable and notifies NTPD via a sha red memory segment. It doesn't get any faster than that for me. Microseconds precision. If nothing else, my desktop equipped with this can be a stratum one NTP t ime source for all of the other systems on my LAN with the shortest possible network delay. I could even open it up to the pool.ntp.org pool of serve rs if I cared to do that. Others who have built these have actually done tha t. -- Gary Eheman Fundamental Software, Inc.
