On 2019-06-25, Chris <xxx.syseng....@gfsys.co.uk> wrote: ... > > Thanks again for the replies. Did a bit of digging this morning and > find that the 1pps sync stuff has been done before. Well, many > years ago in fact and more or less how I had visualised it - ntp > data augmented by the 1 pps signal. Several pointers to the way > forward and it's also supported in the FreeBSD kernel, using either a > pin on a serial or parallel port for the 1 pps. Probably go for > the parallel port, as that avoids the hardware to convert 1 pps > ttl to rs232 levels.
Except most serial ports actually used on computers handle ttl levels just fine. > > Have a Minix mini-itx box with two network ports which only draws > about 12 watts. It has headers for the parallel and serial ports, > so looks ideal to experiment with. Already has FreeBSD 11.2, but > will reinstall 12 at minimum level to get the job done. Not after > perfection, but engineers always want the best result at minimum > cost and timescales :-). A few uS should be more than good enough to > maintain stratum 1 accuracy afaics, as network variables are Stratum 1 says nothing about accuracy. You could have stratum 1 come off smoke signals and have an accurcyof minutes, and a stratum 7 have an accuracy of usec. All it indicates is how many steps the time server is from a hardware time source. It says nothing about how good that time source is, or how good the connection is between servers. > orders of magnitude greater than that. Fun project anyway and > will document once it's working... > > > Chris > _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions