econet and other acorn specific networking • Re: SNTP over econet

OK, I've ordered the hardware, and this is what I intent to implement:

SETP
SETP (Simple Econet Time Protocol) is a client-server time synchronisation protocol, based on SNTP but adapted to the limitations of Econet. It does not cover peer-peer synchronisation between servers, but could probably be extended.

A synchronisation consists of three messages:

1. • The client sends a broadcast (address FF.FF) to port 7B. The 8-byte payload is a random identifier (SyncID) generated to avoid coincidences. The client records the time of transmission (OrgTime) as accurately as possible.
   • The server receives the broadcast, and records the time of arrival (RecvTime) as accurately as possible, along with SyncID and client address.
2. • The server sends a broadcast (address FF.FF) to port 7B, with the same SyncID as its payload. The server records the time of transmission (TransTime) as accurately as possible.
   • The client receives the broadcast (checking SyncID), and records the time of arrival (DestTime) as accurately as possible, along with the server address.
3. • The server sends a 48-byte data-block (based on NTP) to the client address, port &7B.
   • The client receives the data block, and checks that both the SyncID and server address match the broadcast.

The server will ignore further broadcasts with the same SyncID, to avoid messages bouncing between servers. If the client receives multiple replies from different servers, it can either use the first, pick a default, use the rest of the data to judge accuracy, or take an average.

The Data-Block
All times are 64-bit unsigned fixed 32.32 format, with zero at 1900-01-01.00:00:00 UTC, ignoring leap seconds. This will roll-over at 2036-02-07.06:28:16 UTC. The precision is about 232 picoseconds.

Byte	Name	Description	Details
0 bits 0-1	LI	Leap seconds due at end of month	0=0, 1=+1, 2=-1, 3=error
0 bits 2-4	VN	Version number	Must be 4 (current version)
0 bits 5-7	Mode	Protocol mode	Must be 4 (server)
1	Stratum	No. of steps to primary clock	0=kiss-of-death, 1=primary clock
2	Poll interval	Max time between poll messages	unsigned log2 seconds
3	Precision	Server clock precision	signed log2 seconds
4-7	Root delay	roundtrip time to primary clock	signed fixed 16.16 seconds
8-11	Root disp.	max error due to clock frequency	unsigned fixed 16.16 seconds
12-15	Ref. ID	Identifier for server time reference	see NTP for details
16-23	Ref. time	Time server clock was last set	fixed 32.32 seconds since 1900
24-31	SyncID	The identifier used in broadcasts	(in NTP this is OrgTime)
32-39	RecvTime	Time query arrived, on server clock	fixed 32.32 seconds since 1900
40-47	TransTime	Time reply sent, on server clock	fixed 32.32 seconds since 1900

Calculations
Roundtrip time = (DestTime - OrgTime) - (TransTime - RecvTime)
Correction to client clock = (RecvTime - OrgTime) + (TransTime - DestTime)) / 2

All suggestions for improvement welcome!

Statistics: Posted by Barneyntd — Thu Sep 04, 2025 9:12 pm

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