[time-nuts] Serial or other simple protocols for exchanging time
Bob kb8tq
kb8tq at n1k.org
Thu Aug 15 14:56:02 UTC 2019
Hi
Which all sort of begs the question:
Why not a simple “broadcast UDP” once a second time packet approach for a home LAN?
Unless you get really crazy, it’s not going to be a very big packet. Seconds since some
arbitrary point in time. Time zone offset. Maybe a leap second count. Server ID maybe.
Less than 100 bytes not including the overhead.
Bob
> On Aug 15, 2019, at 5:36 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
>
>
> ausserirdischesindgesund at gmail.com said:
>> I am a newbie and am wondering what options there are for exchanging time
>> on a more basic level than NTP or PTP (that is for situations when a
>> full network stack is too complex).
>
> You haven't described your problem fully yet.
>
> Are you interested in client side or server side? (or both)
>
> What sort of environment are you working in? What sort of hardware do you
> have available?
>
> NMEA over a serial port is probably what you want, but...
>
>
> Raspberry Pi and similar are not very expensive. They come with networking
> software. The Pi isn't very nice for time-nut work over the net because the
> Ethernet is on USB which adds jitter and/or hanging bridges. It does have
> GPIO.
>
>
> There is a lot of things you can do without a "full network stack".
>
> What level of hacking is reasonable depends on your environment. For a setup
> at home, you are unlikely to annoy anybody else.
>
> The Alto firmware could boot over the (3 MB) Ethernet. The boot servers would
> periodically send a boot-loader packet to a reserved hardware address. The
> firmware only had to setup the hardware to receive a packet, wait for one,
> sanity check things, and jump to it.
>
> If you use UDP rather than TCP, the "stack" level packet format is much
> simpler. Retransmission becomes trivial if you only have one un-ACKed packet
> to consider. Performance on a LAN is OK most of the time.
>
> For something like a NTP server, you can avoid routing and ARP by sending the
> reply back where it came from.
>
> For the client side, the normal problem is finding the server. If you only
> have one server, you can wire in the address.
>
>
>
>
> --
> These are my opinions. I hate spam.
>
>
>
>
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