On Sun, 6 Mar 2022, Chris Albertson wrote:
Date: Sun, 6 Mar 2022 12:31:23 -0800 From: Chris Albertson <albertson.ch...@gmail.com> Reply-To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Subject: Re: [Emc-users] Pi4 with LinuxCNC and MESA 7i92HWhat is the actual goal? Keep anyone state it in exact terms? In past decades the Ethernet was a shared medium where every device was exposed to every packet sent by any other device. This was back in the time when we used coaxial cables. Then twisted pair Ethernet was invented but we all used "hubs" that simply retransmitted any incoming packet to every other port. This simulated the way coaxial networks worked. Then maybe 20 years ago? We started to use "Ethernet switches". These devices look at the packet header from each inbound packet on each port and only send it out the port it is addressed to. So on a modern Ethernet, a device like a Pi4 or MESA 7i92H never sees Ethernet packets that were not sent to it. OK, there are some broadcasts that are sent to every device. But simply using a modern switched Ethernet gets a LONG ways to an isolated network. My gues is the advice to use dedicated network hardware comes from the era before network switches where common So again, what exactly is the goal? Maybe the goal is not to delay outbound traffic from the Pi4 to the MESA 7i92H? So if the Pi4 is sending data to some web server we do not want our web surfing to be queued ahead of the LCNC related commands. But do you get this effect by installing a second Ethernet port? I doubt it. The only queue in the system is inside the Linux OS. It would be good to know EXACTLY what the problem is,
The bottleneck with a shared Ethernet port is the MAC/Phy which would mean outgoing and incoming real time packets might need to wait for normal (large packet) Internet traffic, adding considerable jitter. This is solved by using a separate physical interface.
Peter Wallace Mesa Electronics _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
