Interesting comments. I will throw a bit more detail in here in case anyone else is or has headed down the same path and may have some tips or ideas to share.
Two or more devices on Ethernet is essentially a network. The ESS is (I am presuming) a popular motion controller for MACH, so the port of my 4th axis motor controller to Ethernet must be compatible. That makes three Ethernet devices in the 'network', hence a switch.
Modern computers can bridge internally so all you need is a second NIC to avoid the switch, and that is the only configuration where I would consider having any other Ethernet traffic for the PC to process. However, I am hoping the ESS address is configurable. My controller is somewhat similar to ESS in that it communicates with MACH thru a software interface to exchange data, but the step/dir signals are generated in dedicated on-board hardware. Fortunately, my controller does not have to deal with positioning, so there is no buffer, and in MACH4 the scan thru Ethernet Modbus is pretty quick . . to say the least.
In the sandbox will go the Motion controller's buffer, GB Ethernet speed, my controller hitting the Ethernet Modbus at less than 100hz with tiny packets. It won't take long to know if these kids are going to play nice together. Pappabear has the bit packing figured out, if I recall correctly, (I am not following this stuff closely) and as usual, has generously shared that information, so I can study that if needed and significantly reduce the volume of data passed to the controller.
The last snafu on my end was that the controller's processor stores params in non volatile memory and the new DUE board has none, but I have that problem solved so all of the puzzle pieces are in place. I have purchased MACH4 and I want the ESS and hopefully also the PDMX (426, I think it is) both in house before I start porting over to MACH4. The PDMX thread has gone quiet and Kflop does not seem to have any priority assigned to MACH4 so I may start with just the ESS when my schedule allows.
Jeff, thanks for the quick response and answers.
I will be purchasing from you and I recommend you as the preferred ESS source. Price is not an issue as your expertise and willingness to share it is beyond any reasonable expectation for a product at this price point . . . . . in my opinion. It is also encouraging that the developer is participating in the forum as well.