Ethernet for serial data.

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Lostgallifreyan
Posts: 83
Joined: Thu Jan 12, 2023 8:25 pm

Ethernet for serial data.

Post by Lostgallifreyan »

Given the inaccuracy of network time because of latency, variable server access, it is better to use a GPS module, and a Psion Organiser could be used to make an accurate time server on a LAN, probably as good as a Tier 1 NTP server, based on NMEA RMC with a 10 Hz report rate.

What method is best for converting between serial data and ethernet packets? It's likely that more tools than GPS modules can use such a thing, so I think there may be several good methods.

A Raspberry Pi might be ideal, and fast, but it's still a sledgehammer to crack a nut. Machine code on an Organiser might be a better way to make the packets (and parse them), so maybe the problem is reducible to converting a serial byte to an Ethernet byte (and vice versa) with minimal hardware with an RJ45 socket and enough 'brain' to set an address range and static IP via serial commands.

Any answer must be easy, otherwise it would be better to use the most available PC to get NMEA data directly via serial data and use a local time server based on software for other machines on a LAN to connect to, but he idea is NOT to have to do that because an Organiser might be a way to do it efficiently and independently of any other machine.

Given that Bluetooth is ideal for getting serial NMEA data over a distance of several tens of metres, a Bluetooth module that converts serial to ethernet is a very tempting notion because it would make it very easy to find somewhere to put each end of the system and not have any cable layout to do. I don't know if a serial-over-Bluetooth widget exists that has an RJ45 socket for use on a LAN exists, but it might be the best possible answer if it does, even if it means not using an Organiser in the data path, but having the Organiser inserted between a GPS module and a serial-to-Bluetooth widget does present interesting possibilities even if it's not used as part of ethernet packet handling...
amenjet
Posts: 179
Joined: Tue Jan 03, 2023 7:54 pm

Re: Ethernet for serial data.

Post by amenjet »

You can get serial to ethernet modules fairly cheaply. To get an ethernet port on an Organiser top slot would be quite a job. The RMII/RGMII interface to the PHY is quite a fast interface and beyond the top slot hardware. You'd probably have to essentially build a serial to ethernet adapter, so you may as well buy a module.

Andrew
Lostgallifreyan
Posts: 83
Joined: Thu Jan 12, 2023 8:25 pm

Re: Ethernet for serial data.

Post by Lostgallifreyan »

Thanks. A quick search for "RMII/RGMII interface to the PHY" (minus quotes) shows me stuff to convince me not to try reinventing that wheel.

I'm not familiar with these serial-to-ethernet devices, so please name at least two you think are worth looking into, that way I can narrow the search without missing something that might be important. SNR on general web searches is so low I can use the help..

I'm currently writing a Win32 program (based on big chunks of ORG-Link so will look vaguely familiar when it's done) to act as a GPS clock and UDP broadcaster on a LAN. The timing is very sharp (enough to detect that the BBC's Greenwich pips are very slightly late), so I may decide that an Organiser is too slow anyway, a Raspberry Pi might be a useful tool, though likely too versatile to want to use that way indefinitely.
amenjet
Posts: 179
Joined: Tue Jan 03, 2023 7:54 pm

Re: Ethernet for serial data.

Post by amenjet »

I've never used one, but a module called the HLK-RM04 seems to be an RS232/serial to ethernet adapter. Looks like it does wifi too, somehow.

Andrew
Lostgallifreyan
Posts: 83
Joined: Thu Jan 12, 2023 8:25 pm

Re: Ethernet for serial data.

Post by Lostgallifreyan »

Thanks. I looked into that for a few minutes, and found this:
https://rayshobby.net/wordpress/first-i ... fi-module/

I think I'm out of my depth for now, it's interesting but there are no fast or easy answers that way. What's odd is that the page started in 2014 I think, and nearly ten years later, maybe there still aren't....
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