Ethernet VS USB

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Dave_C
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Ethernet VS USB

Post by Dave_C »

Dave_C,
you are still preaching the "faith" reason for not using an USB-Ethernet adapter but you haven't given one good fact other than "Centroid said". The fact that Windows could interrupt CNC operations with messages is a general Windows issue and not Ethernet Adapter specific.

-swissi
So whiteout writing a white paper on Computer science I'll just copy some data from an online article:

USB is a serial bus.

It uses 4 shielded wires: two for power (+5v & GND) and two for differential data signals (labelled as D+ and D- in pinout).

In a USB data cable Data+ and Data- signals are transmitted on a twisted pair with no termination needed. Half-duplex differential signaling is used to reduce the effects of electromagnetic noise on longer lines. D+ and D- operate together; they are not separate simplex connections.

USB supports four data rates:

Low Speed (1.5 Mbit per second) that is mostly used for Human Input Devices (HID) such as keyboards, mice, joysticks and often the buttons on higher speed devices such as printers or scanners;

Full Speed (12 Mbit per second) which is widely supported by USB hubs.

Hi-Speed (480 Mbit per second) was added in USB 2.0 specification. Not all USB 2.0 devices are Hi-Speed.

SuperSpeed (USB 3.0) rate of 4800 Mbit/s (~572 MB/s).

A USB device must indicate its speed by pulling either the D+ or D- line high to 3.3 volts. These pull up resistors at the device end will also be used by the host or hub to detect the presence of a device connected to its port. Without a pull up resistor, USB assumes there is nothing connected to the bus.

My input from here:

USB is a BUS and as such it has to share its workload with all other USB attached peripherals such as Keyboards, Mouse, Printer and all other such USB items.

USB is not full duplex!

USB only has a 2 wire transmit receive setup, while Ethernet is full duplex.

USB takes 20% of the available speed for housekeeping (overhead)

The real details are easily found by doing simple Internet searches so if you want to learn more, just google your questions until you are satisfied that Ethernet and USB are not the same!

Dave C.
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martyscncgarage
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Re: Ethernet VS USB

Post by martyscncgarage »

USB is not my first choice for motion control. Especially if its on a laptop. Power saving/suspend features etc.....

Ethernet is far better.
Reminder, for support please follow this post: viewtopic.php?f=20&t=383
We can't "SEE" what you see...
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swissi
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Re: Ethernet VS USB

Post by swissi »

Dave_C,

thanks to open anew thread for this subject but you completely missed the point I was trying to make. I never claimed that USB and Ethernet are the same and I don't think anybody would dispute that a genuine Ethernet port is the superior interface over an Ethernet connection through an Ethernet to USB adapter.

Also nobody would dispute that a large pickup truck is superior over a compact car if you have to pickup 1 ton of cement at the hardware store but if your task is to pickup a gallon of milk at the grocery store, the compact car is the more efficient option.

I always smile about the car commercials that claim their car is the best in its class. That statement doesn't mean anything if you don't specify exactly what that class is and which other cars are in it. The same is true with the technical specs you listed about the USB port. If you don't specify what limitation these specs impose to operating an Acorn controlled machine they don't mean much.

My real point is that so far I have only seen peoples opinion against an USB to Ethernet adapter based on faith and trust and not on quantified facts in relation to Acorn CNC operations.

Looking at the specs, we could see USB not being full duplex or having limited speed being a problem but I'm running two Acorns on Ethernet to USB adapters and I have not encountered any issues so far but I'm not saying that there couldn't be any.

What I'd like to know is if there's anybody out there that has run into or knows about issues that where related to running CNC12 over USB. I could see that the PC could not keep the Beagle board busy with very complex jobs but so far I have never run into this issue. If anybody has data if the Beagle board would even be fast enough to handle more command lines than the USB Ethernet connection could supply, that would be good to know.

People might have computers without an Ethernet adapter and we should not tell them not to use an Ethernet to USB adapter just because we have no "faith" in them. A better answer would be: We do not recommend it because it has these known limits x in CNC12 operations but as long as you stay within these limits it will work. And it's also ok to say: If you choose to use such an adapter, you won't get any support if you have any communication issues.

Once again, a Ferrari is a superior car over a Camry but we would not tell people they need to buy a Ferrari unless we could tell them exactly why the Camry would not be sufficient.

So if anybody has encountered or knows about proven limitations of CNC12 machine operation over an Ethernet to USB adapter, please come forward.

-swissi
If you are using Fusion 360, check out my CNC12 specific Post Processor
If you are using a Touch Probe, Tool Touch Off Device or a Triple Corner Finder Plate, check out my ProbeApp

Contact me at swissi2000@gmail.com
DannyB
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Re: Ethernet VS USB

Post by DannyB »

I'll go further than this:

What was posted is definitely no longer true, but you have to at least know enough about what you are doing.
Let's assume that ethernet over usb-bus itself is a complete no-go for *whatever* reason.

USB 3.1+ is in fact, mostly a connector/electrical specification at this point
It supports many different types of interfaces over that connector.

Thunderbolt 3 (using a USB-C connector) is literally just PCIe over a different type of cable.
(PCIe itself is already a network bus)

The lanes are routed to it the same way they are with card connectors inside the computer, etc.

With a thunderbolt3 based network adapter connected to a usb-c port, there is literally no difference between having an adapter internal to the computer or external.
Period.

In fact, you can, if you wanted to be crazy, actually just move all the internal cards in your computer to somewhere else and just connect thunderbolt between your computer and somewhere else. They won't be able to tell the difference.

See, eg, https://www.sonnettech.com/product/echo ... rview.html or

So even if there ever *was* a reason not to use a usb based ethernet adapter in the past based on bandwidth or whatever, there shouldn't be one now if you choose one that is thunderbolt->usbc

(Cycle time was never a concern as PCIe is in the low nanoseconds to transfer data)
Dave_C
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Re: Ethernet VS USB

Post by Dave_C »

Has anyone built from scratch a real "High End" computer?

I'm sure many have, but ask yourself this. Why do the high end gaming Mother Board Manufacturers still include a PS2 port?

It is because the high end competitive gamers don't like the time delay when using a USB keyboard!

USB is, or can be very fast but has wait states while the bus looks for other input request from other attached USB items, so real competitive gamers who need instant response when they hit a keystroke use PS2 keyboards.

USB has cable length restrictions of no more than 15 feet and that is pushing it while Ethernet can go up to 300 feet or more depending on certain issues.

I am way too old to play games and I've forgotten way too much to stay in this silly argument so I'm standing down. IF you want to use USB, that is your choice...and your responsibility.

I just finished an 8 core 4.1Ghz, 32 gig of 3200 mem, ASUS motherboard and I use a PS2 keyboard! Not for gaming but very intensive 4K video editing and narration.

Back to the playoff games,

Dave C.
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Re: Ethernet VS USB

Post by slodat »

I believe PS2 port allows more simultaneous key presses than USB's HMI interface. I think I read this when looking at 3dConnexion SpaceMouse stuff.
Dave_C
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Re: Ethernet VS USB

Post by Dave_C »

I believe PS2 port allows more simultaneous key presses than USB's HMI interface. I think I read this when looking at 3dConnexion SpaceMouse stuff.
True!

Dave C.
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Re: Ethernet VS USB

Post by DannyB »

Dave_C wrote: Sun Jan 05, 2020 4:43 pm Has anyone built from scratch a real "High End" computer?
...


Dave C.
Yes, I have. I'm also very friendly with the folks who designed the usb-c connector and have attended various USB wg/if meetings in the past.

Nothing you just wrote is relevant to what I wrote (as it mostly concerns the hci spec), and what you wrote is very wrong in various ways.

The keyboard stuff is because they are using the low speed spec which has a minimum packet latency of 10ms. Not related to anything you would ever do with Ethernet, and definitely not relevant to the situation I described.

USB 2.0 polled at 0.125ms.
USB 3.0 *is not polling based*. It is *not* a shared bus system. It is a point to point link system. It is not looking at anything or locking.
Most devices achieve latency in the 10-20us range easily (time from device to random Windows App seeing it).
Here is a random example:
https://stackoverflow.com/a/26918988

A standard USB 3.0 (ie not thunderbolt) gigabit Ethernet adapter has identical user facing latency to a non USB one no matter what else is connected.

I can show you them running in hard real-time systems.

The thunderbolt over USB ones, as I said, are not distinguishable in a meaningful way from a card plugged into your computer.
Same bus, etc.

If you would like me to show you 10gb thunderbolt over usb-c adapter achieving 1 microsecond latency I'm happy to.

The practical max length limit for USB 3.0/3.1 speeds is about 60 feet. I can show you it working fine at that distance and speed with a normal spec meeting cable. It does require using appropriate gauge signal wire, etc (same as Ethernet)

For when USB is used as the electrical connector but not the bus, as I mentioned, it is even longer. For example, thunderbolt has a max cable length of 100 meters (same as Ethernet actually).

Your information is true and correct for USB as a bus as it was used and existed until 2.0, but it's really just not how it is done anymore.

It's fine if you choose not to use it for whatever reason, but let's not spread misinformation about capability
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Re: Ethernet VS USB

Post by Dave_C »

It's fine if you choose not to use it for whatever reason, but let's not spread misinformation about capability
That's all well and good but how many of these computers being used for CNC today actually have a USB3.0 or 3.1?

When Centroid says they support USB, I'll change my opinion but in the meantime, I'll go with Centroids recommendation since they are the creators of the Acorn Boards and they are a lot smarter than I am. (A lot younger too)

Dave C.
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Re: Ethernet VS USB

Post by DannyB »

Basically every computer manufactured since ~2010 has USB 3.0 (the first computers were earlier than that, but this is when it was the default for everyone)

The NUC centroid sells and ships now on their website (NUC8i3BEK1) has USB 3.1 gen 2
The NUC they sold before that on their website (NUC7i3BNH) has USB 3.1 gen 2.

Their recommended cncpc builds have usb 3.1 gen 2 (viewtopic.php?f=64&t=2794)

Look, you went with some info that was not right, and rather than saying "yeah, i was wrong", now you are trying to deflect to something else.
We all are wrong sometimes, and there is no shame in it.

Like I said, you can go with what you want, based on whoever's opinion you want to value, but let's at least keep correct info here. That is what helps people the most in the end.
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