Chinese CNC 3020 / 6040 - USB variant

Todd, your being hostile.
so basically programmers like you just want to do your own thing without even trying to accept or understand the requests of others.
I made a clear and concise argument so to converse with you further would be a waste of oxygen.

Linuxcnc is a machine controller with all the bells and whistles that go with it, so real time is real requirement.
USB can not do real time, not by a long shot, it is inherently impossible to do control a machine through it.
There are solutions around it, like mach3 and some controller boards for it, but still it is not real time as stopping the machine while working or messing something up will last long enough for the machine to do it's thing, leaving the user with tears while watching the messed up machine.
On the brighter side of things, if you insist on using Linuxcnc through USB, search for DaBit, he did make it work to a certain extent quite well.
And i agree with Todd, parallel port is not going away any time soon, it is direct access hardware and that makes it very usable fur such needs, and it is very cheap.

Sorry if I'm coming off as hostile, don't mean to. I am by no means or in any way shape or form a programmer. (I don't even know what a HID is that you refereed to in your earlier post.) I'm just a lowly user/integrator (I've set up 8 machines with Linuxcnc) who has been extremely happy with what I've found in Linuxcnc. It has saved our company thousands of dollars, and increased machine productivity.

Neither am I a real-time expert. I only know what I've been told, and that is that USB doesn't work with real-time. You can still use USB with Linuxcnc for non real-time tasks, such as controlling a spindle VFD and HMI stuff. I've done both. My understanding also is that Ethernet can be marginal for real-time and that not all Ethernet hardware is real-time capable but I have no experience with trying it out.

Two of the machines I've set up used Mesa PCI cards, the rest have all used parallel ports. And for all of those parallel port machines, that has been perfectly adequate for their application and spending more money for some other interface would have been a waste.

If you review the USB CNC controller candidates, they have the motion controller embedded in a microchip on board. These came about in the Windows world where they have a non real time operating system.

Linuxcnc on the other hand IS THE MOTION CONTROLLER and it needs to operate in real time. This brings significant advantage to CNC because the PC based motion controller has vastly more resources in terms of memory and CPU processing power than a smooth stepper style board.

By design, USB has a serial protocol and is incapable of acting in real time so its not possible for it to be used to feed a real time motion loop as packets will arrive late. To buffer the input defeats the whole purpose of having a real time servo loop.

So the real point of difference with LInuxCNC is that it is the Motion controller. So your choices are to embrace the wonderful advantages that comes with the LInuxcnc paradigm or look to another solution that does motion control on a very limited external board..

By the time you pay for a Mach 3 license and a smooth stepper step generator it cost more than the Mesa card

I think the best in Linuxcnc :

If you want usb driver, sit down and write one.

m5c
Mike