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USB "null modem" cables and related Linux driver questions

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  USB "null modem" cables and related Linux driver questions Richard Owlett <rowlett@cloud85.net> - 2018-05-31 16:30 +0200
    Re: USB "null modem" cables and related Linux driver questions Reco <recoverym4n@gmail.com> - 2018-05-31 16:50 +0200
    Re: USB "null modem" cables and related Linux driver questions Dan Ritter <dsr@randomstring.org> - 2018-05-31 18:10 +0200
      Re: USB "null modem" cables and related Linux driver questions Richard Owlett <rowlett@cloud85.net> - 2018-06-01 11:50 +0200
    Re: USB "null modem" cables and related Linux driver questions David Wright <deblis@lionunicorn.co.uk> - 2018-06-01 02:00 +0200
      Re: USB "null modem" cables and related Linux driver questions Richard Owlett <rowlett@cloud85.net> - 2018-06-01 12:00 +0200
        Re: USB "null modem" cables and related Linux driver questions <tomas@tuxteam.de> - 2018-06-01 12:30 +0200
          Re: USB "null modem" cables and related Linux driver questions Stefan Monnier <monnier@iro.umontreal.ca> - 2018-06-01 14:30 +0200
            Re: USB "null modem" cables and related Linux driver questions <tomas@tuxteam.de> - 2018-06-01 15:30 +0200
              Re: USB "null modem" cables and related Linux driver questions Richard Owlett <rowlett@cloud85.net> - 2018-06-01 16:10 +0200
                Re: USB "null modem" cables and related Linux driver questions David Wright <deblis@lionunicorn.co.uk> - 2018-06-02 06:50 +0200
                Re: USB "null modem" cables and related Linux driver questions Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2018-06-07 06:50 +0200
                  Re: USB "null modem" cables and related Linux driver questions Curt <curty@free.fr> - 2018-06-07 11:00 +0200
        Re: USB "null modem" cables and related Linux driver questions Michael Stone <mstone@debian.org> - 2018-06-01 16:10 +0200
          Re: USB "null modem" cables and related Linux driver questions Joe <joe@jretrading.com> - 2018-06-01 19:40 +0200
          Re: USB "null modem" cables and related Linux driver questions Richard Owlett <rowlett@cloud85.net> - 2018-06-01 21:20 +0200
            Re: USB "null modem" cables and related Linux driver questions Andy Smith <andy@strugglers.net> - 2018-06-01 23:10 +0200
            Re: USB "null modem" cables and related Linux driver questions Michael Stone <mstone@debian.org> - 2018-06-02 02:50 +0200
    Re: USB "null modem" cables and related Linux driver questions Stefan Monnier <monnier@iro.umontreal.ca> - 2018-06-01 05:10 +0200
      Re: USB "null modem" cables and related Linux driver questions Stefan Monnier <monnier@iro.umontreal.ca> - 2018-06-01 05:20 +0200
      Re: USB "null modem" cables and related Linux driver questions Richard Owlett <rowlett@cloud85.net> - 2018-06-01 12:30 +0200
        Re: USB "null modem" cables and related Linux driver questions Stefan Monnier <monnier@iro.umontreal.ca> - 2018-06-01 14:30 +0200
        Re: USB "null modem" cables and related Linux driver questions Gene Heskett <gheskett@shentel.net> - 2018-06-01 19:40 +0200
    Re: USB "null modem" cables and related Linux driver questions deloptes <deloptes@gmail.com> - 2018-06-01 08:30 +0200
      Re: USB "null modem" cables and related Linux driver questions <tomas@tuxteam.de> - 2018-06-01 10:30 +0200
      Re: USB "null modem" cables and related Linux driver questions Richard Owlett <rowlett@cloud85.net> - 2018-06-01 12:30 +0200
        Re: USB "null modem" cables and related Linux driver questions David Wright <deblis@lionunicorn.co.uk> - 2018-06-01 16:20 +0200
    Re: USB "null modem" cables and related Linux driver questions Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2018-06-07 06:50 +0200
      Re: USB "null modem" cables and related Linux driver questions Tixy <tixy@yxit.co.uk> - 2018-06-07 09:10 +0200
        Re: USB "null modem" cables and related Linux driver questions Michael Stone <mstone@debian.org> - 2018-06-07 14:40 +0200
    Re: USB "null modem" cables and related Linux driver questions David <bouncingcats@gmail.com> - 2018-06-18 14:20 +0200
      Re: USB "null modem" cables and related Linux driver questions Michael Stone <mstone@debian.org> - 2018-06-18 14:50 +0200
        Re: USB "null modem" cables and related Linux driver questions rhkramer@gmail.com - 2018-06-18 16:00 +0200
      Re: USB "null modem" cables and related Linux driver questions Richard Owlett <rowlett@cloud85.net> - 2018-06-18 15:40 +0200

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#196293 — USB "null modem" cables and related Linux driver questions

I have two computers with USB ports.
I wish them to communicate as simply as mid-20th-century computers did.
Then we used RS232-C with a null modem &/or  appropriate software 
software at both ends.

The underlying problem is that both ends egotistically expect to be 
*MASTER*.

The hardware problem is solvable [e.g. 
http://www.ftdichip.com/Products/Cables/USBtoUSB.htm].

The software is another case :<
The best Linux specific link I've found is dated September 2005 
[http://www.linux-usb.org/usbnet/]

I've done DuckDuckGo searches for permutations/combinations of
   usb, "peer to peer", lan, and bridge.
Most is Windows/Mac centric.
There were hints that needed drivers may exist in current Linux core.

Pointers to good references and/or better search terms?
TIA

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#196295

	Hi.

On Thu, May 31, 2018 at 09:21:27AM -0500, Richard Owlett wrote:
> I have two computers with USB ports.
> I wish them to communicate as simply as mid-20th-century computers did.
> Then we used RS232-C with a null modem &/or  appropriate software software
> at both ends.
> 
> The underlying problem is that both ends egotistically expect to be
> *MASTER*.

I did the thing in the not-so-distant past.

It took two USB-RS232 converters (FDTI chipsets should work out of the
box), and a conventional RS232 null modem cable. Communication was
limited to 112500 bps, but I needed it for the serial console anyway.

As for the software part, agetty and minicom were all that was needed.

Reco

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#196298

On Thu, May 31, 2018 at 09:21:27AM -0500, Richard Owlett wrote:
> I have two computers with USB ports.
> I wish them to communicate as simply as mid-20th-century computers did.
> Then we used RS232-C with a null modem &/or  appropriate software software
> at both ends.
> 
> The underlying problem is that both ends egotistically expect to be
> *MASTER*.
> 
> The hardware problem is solvable [e.g.
> http://www.ftdichip.com/Products/Cables/USBtoUSB.htm].
> 
> The software is another case :<
> The best Linux specific link I've found is dated September 2005
> [http://www.linux-usb.org/usbnet/]
> 
> I've done DuckDuckGo searches for permutations/combinations of
>   usb, "peer to peer", lan, and bridge.
> Most is Windows/Mac centric.
> There were hints that needed drivers may exist in current Linux core.
> 
> Pointers to good references and/or better search terms?

Do you want:

- One end is a terminal, the other end offers login?   "agetty
  serial" and "minicom"

- TCP/IP over RS-232 serial?   Keyword is "PPP".

- TCP/IP over ethernet attached via USB? "usbnet" and treat them
  like ethernet adapters.

- Connect an actual hardware terminal like a VT320 to your Linux
  box? "agetty serial" again.

- Something else? Describe it.

-dsr-

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#196318

On 05/31/2018 11:07 AM, Dan Ritter wrote:
> On Thu, May 31, 2018 at 09:21:27AM -0500, Richard Owlett wrote:
>> I have two computers with USB ports.
>> I wish them to communicate as simply as mid-20th-century computers did.
>> Then we used RS232-C with a null modem &/or  appropriate software software
>> at both ends.
>>
>> The underlying problem is that both ends egotistically expect to be
>> *MASTER*.
>>
>> The hardware problem is solvable [e.g.
>> http://www.ftdichip.com/Products/Cables/USBtoUSB.htm].
>>
>> The software is another case :<
>> The best Linux specific link I've found is dated September 2005
>> [http://www.linux-usb.org/usbnet/]
>>
>> I've done DuckDuckGo searches for permutations/combinations of
>>    usb, "peer to peer", lan, and bridge.
>> Most is Windows/Mac centric.
>> There were hints that needed drivers may exist in current Linux core.
>>
>> Pointers to good references and/or better search terms?
> 
> Do you want:
> 
> - One end is a terminal, the other end offers login?   "agetty
>    serial" and "minicom"
> 
> - TCP/IP over RS-232 serial?   Keyword is "PPP".
> 
> - TCP/IP over ethernet attached via USB? "usbnet" and treat them
>    like ethernet adapters.
> 
> - Connect an actual hardware terminal like a VT320 to your Linux
>    box? "agetty serial" again.

Seeing those references mentioned together in this context gives me 
hints towards understanding some of what I've read.

> 
> - Something else? Describe it.

Your list pretty much covers it.
Also a curiosity bump that's been around since USB 1.0 .

> 
> -dsr-
> 

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#196307

On Thu 31 May 2018 at 09:21:27 (-0500), Richard Owlett wrote:
> I have two computers with USB ports.
> I wish them to communicate as simply as mid-20th-century computers did.
> Then we used RS232-C with a null modem &/or  appropriate software
> software at both ends.

I remember soldering these cables together. It always seemed crazy to
be paying as much for a cable as a floppy drive.

> The underlying problem is that both ends egotistically expect to be
> *MASTER*.
> 
> The hardware problem is solvable [e.g.
> http://www.ftdichip.com/Products/Cables/USBtoUSB.htm].

https://shop.clickandbuild.com/cnb/shop/ftdichip?op=catalogue-products-null&prodCategoryID=354&title=Null+Modem+Cables
(thanks for your link) gives an idea of the price, and in this case I
can see some justification for it because they describe the
electronics hidden inside the plugs (we hope).

But considering that two NICs cost less than that cable, I'd need a
pressing reason to purchase the cable instead.

> The software is another case :<
> The best Linux specific link I've found is dated September 2005
> [http://www.linux-usb.org/usbnet/]
> 
> I've done DuckDuckGo searches for permutations/combinations of
>   usb, "peer to peer", lan, and bridge.
> Most is Windows/Mac centric.
> There were hints that needed drivers may exist in current Linux core.
> 
> Pointers to good references and/or better search terms?

"ppp over usb" gave me http://www.linux-usb.org/usbnet/
which might be what you want. I notice that such a module is
in the production kernels.

Cheers,
David.

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#196319

On 05/31/2018 06:58 PM, David Wright wrote:
> On Thu 31 May 2018 at 09:21:27 (-0500), Richard Owlett wrote:
>> I have two computers with USB ports.
>> I wish them to communicate as simply as mid-20th-century computers did.
>> Then we used RS232-C with a null modem &/or  appropriate software
>> software at both ends.
> 
> I remember soldering these cables together. It always seemed crazy to
> be paying as much for a cable as a floppy drive.
> 
>> The underlying problem is that both ends egotistically expect to be
>> *MASTER*.
>>
>> The hardware problem is solvable [e.g.
>> http://www.ftdichip.com/Products/Cables/USBtoUSB.htm].
> 
> https://shop.clickandbuild.com/cnb/shop/ftdichip?op=catalogue-products-null&prodCategoryID=354&title=Null+Modem+Cables
> (thanks for your link) gives an idea of the price, and in this case I
> can see some justification for it because they describe the
> electronics hidden inside the plugs (we hope).
> 
> But considering that two NICs cost less than that cable, I'd need a
> pressing reason to purchase the cable instead.

There is a perceived elegance aspect.
There is also a practical aspect the only known working and conveniently 
physically accessible ports are USB.

> 
>> The software is another case :<
>> The best Linux specific link I've found is dated September 2005
>> [http://www.linux-usb.org/usbnet/]
>>
>> I've done DuckDuckGo searches for permutations/combinations of
>>    usb, "peer to peer", lan, and bridge.
>> Most is Windows/Mac centric.
>> There were hints that needed drivers may exist in current Linux core.
>>
>> Pointers to good references and/or better search terms?
> 
> "ppp over usb" gave me http://www.linux-usb.org/usbnet/
> which might be what you want. I notice that such a module is
> in the production kernels.

I had seen the page. It told me that I was not pursuing an 
impossibility. I was hoping for a more recent reference than 2005.



> 
> Cheers,
> David.
> 
> 

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#196321

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On Fri, Jun 01, 2018 at 04:56:32AM -0500, Richard Owlett wrote:

[...]

> >>Pointers to good references and/or better search terms?
> >
> >"ppp over usb" gave me http://www.linux-usb.org/usbnet/
> >which might be what you want. I notice that such a module is
> >in the production kernels.
> 
> I had seen the page. It told me that I was not pursuing an
> impossibility. I was hoping for a more recent reference than 2005.

Perhaps this helps you in your research.

As you've found out by now, USB is an asymmetric protocol: each
network has a "boss" and the rest are all subordinates (perhaps
this design reflects the organization structures in the involved
companies [1], but I disgress).

Of course, some folks always wanted to connect two devices with
enough "personality" that they both wanted to be masters.

The one choice you have is that one of both sides takes a step
back and plays "gadget" (the jargon term, somewhat unfortunate
as search engine fodder). There seems to be something out there
for that, e.g. [2].

The other choice seems to be USB On The Go (aka "OTG") [3]. You
seem to need a special cable for that.

There seem to be Linux drivers to let the USB "stack" play along
with OTG [4], but I have no experience whatsoever with this

Now you have some terms to feed your favourite search engine
(hopefully not The Goog, but I disgress again ;)

Cheers

[1] There's a name for this: Conway's law
    (https://en.wikipedia.org/wiki/Conway%27s_law)
    And those companies? Well, Compaq, DEC, IBM, Intel, Microsoft,
    NEC, and Nortel. 'Nuff said ;-)

[2] https://www.kernel.org/doc/html/latest/driver-api/usb/gadget.html

[3] https://en.wikipedia.org/wiki/USB_On-The-Go

[4] https://superuser.com/questions/1051005/how-to-determine-usb-otg-mode-on-linux

- -- tomás
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=Hhee
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#196324

> The one choice you have is that one of both sides takes a step
> back and plays "gadget" (the jargon term, somewhat unfortunate
> as search engine fodder). There seems to be something out there
> for that, e.g. [2].

The gadget API is the programming API offered by the kernel for the OTG
ports: no OTG => no gadget!

> The other choice seems to be USB On The Go (aka "OTG") [3].
> You seem to need a special cable for that.

More importantly, the USB ports which support OTG are driven by
different hardware.

> There seem to be Linux drivers to let the USB "stack" play along
> with OTG [4], but I have no experience whatsoever with this

Right, you need both your hardware's USB port to support OTG and you
need your kernel to have a driver that supports this hardware.
AFAIK the driver is usually available.


        Stefan

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#196326

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On Fri, Jun 01, 2018 at 08:23:42AM -0400, Stefan Monnier wrote:
> > The one choice you have is that one of both sides takes a step
> > back and plays "gadget" [...]

> The gadget API is the programming API offered by the kernel for the OTG
> ports: no OTG => no gadget!
> 
> > [OTG]

> More importantly, the USB ports which support OTG are driven by
> different hardware.

Ah, so the hardware has to play along...

> Right, you need both your hardware's USB port to support OTG and you
> need your kernel to have a driver that supports this hardware.
> AFAIK the driver is usually available.

Did I say I was handwaving?

Thanks for the clarifications!

Cheers
- -- tomás
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#196328

On 06/01/2018 08:21 AM, tomas@tuxteam.de wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On Fri, Jun 01, 2018 at 08:23:42AM -0400, Stefan Monnier wrote:
>>> The one choice you have is that one of both sides takes a step
>>> back and plays "gadget" [...]
> 
>> The gadget API is the programming API offered by the kernel for the OTG
>> ports: no OTG => no gadget!
>>
>>> [OTG]
> 
>> More importantly, the USB ports which support OTG are driven by
>> different hardware.
> 
> Ah, so the hardware has to play along...
> 
>> Right, you need both your hardware's USB port to support OTG and you
>> need your kernel to have a driver that supports this hardware.
>> AFAIK the driver is usually available.
> 
> Did I say I was handwaving?
> 
> Thanks for the clarifications!
> 

It also suggests that I frequently grasp some of the implications of 
what I read. Thank you.
As an illustration of my mindset:
If they had really intended USB to be *UNIVERSAL* serial bus, then it 
should have been OTG from the get go.
P.S. I know of thousands of reasons they did not.
      Vast majority preceded by $ ;/

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#196343

On Fri 01 Jun 2018 at 09:08:53 (-0500), Richard Owlett wrote:
> On 06/01/2018 08:21 AM, tomas@tuxteam.de wrote:
> >On Fri, Jun 01, 2018 at 08:23:42AM -0400, Stefan Monnier wrote:
> >>>The one choice you have is that one of both sides takes a step
> >>>back and plays "gadget" [...]
> >
> >>The gadget API is the programming API offered by the kernel for the OTG
> >>ports: no OTG => no gadget!
> >>
> >>>[OTG]
> >
> >>More importantly, the USB ports which support OTG are driven by
> >>different hardware.
> >
> >Ah, so the hardware has to play along...
> >
> >>Right, you need both your hardware's USB port to support OTG and you
> >>need your kernel to have a driver that supports this hardware.
> >>AFAIK the driver is usually available.
> >
> >Did I say I was handwaving?
> >
> >Thanks for the clarifications!
> >
> 
> It also suggests that I frequently grasp some of the implications of
> what I read. Thank you.
> As an illustration of my mindset:
> If they had really intended USB to be *UNIVERSAL* serial bus, then
> it should have been OTG from the get go.
> P.S. I know of thousands of reasons they did not.
>      Vast majority preceded by $ ;/

I think you're misunderstanding the use of the word universal.
USB was designed to be a universal way of connecting "any"
peripherals to a PC (sensu lato) which acts as a unique,
controlling host for them.

It wasn't designed to duplicate networking hardware, communicating
between multiple hosts. Nor was OTG. OTG was designed to allow, for
example, what's normally a peripheral to be disconnected from the
host, be connected to a peripheral and effectively become a host
controlling it. Eg, a camera could act as a peripheral while
uploading photos to a PC, then act as a host when connected to an
inkjet to print them.

Cheers,
David.

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#196458

Richard Owlett <rowlett@cloud85.net> writes:

> On 06/01/2018 08:21 AM, tomas@tuxteam.de wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> On Fri, Jun 01, 2018 at 08:23:42AM -0400, Stefan Monnier wrote:
>>>> The one choice you have is that one of both sides takes a step
>>>> back and plays "gadget" [...]
>>
>>> The gadget API is the programming API offered by the kernel for the OTG
>>> ports: no OTG => no gadget!
>>>
>>>> [OTG]
>>
>>> More importantly, the USB ports which support OTG are driven by
>>> different hardware.
>>
>> Ah, so the hardware has to play along...
>>
>>> Right, you need both your hardware's USB port to support OTG and you
>>> need your kernel to have a driver that supports this hardware.
>>> AFAIK the driver is usually available.
>>
>> Did I say I was handwaving?
>>
>> Thanks for the clarifications!
>>
>
> It also suggests that I frequently grasp some of the implications of
> what I read. Thank you.
> As an illustration of my mindset:
> If they had really intended USB to be *UNIVERSAL* serial bus, then it
> should have been OTG from the get go.
> P.S. I know of thousands of reasons they did not.
>      Vast majority preceded by $ ;/

This depends on what you mean by "universal".  It was intended to be a
protocol for computers to use to communicate with peripherals;
"universal" in this context was restricted to peripherals.

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#196464

On 2018-06-07, Joe Pfeiffer <pfeiffer@cs.nmsu.edu> wrote:
>
> This depends on what you mean by "universal".  It was intended to be a
> protocol for computers to use to communicate with peripherals;
> "universal" in this context was restricted to peripherals.

And to the planet earth rather than all the way to the furthest reaches
of the cosmos and back as I doubt whether the folks living out by
Kepler-16 have much use for them.

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#196327

On Fri, Jun 01, 2018 at 04:56:32AM -0500, Richard Owlett wrote:
>On 05/31/2018 06:58 PM, David Wright wrote:
>>(thanks for your link) gives an idea of the price, and in this case I
>>can see some justification for it because they describe the
>>electronics hidden inside the plugs (we hope).
>>
>>But considering that two NICs cost less than that cable, I'd need a
>>pressing reason to purchase the cable instead.
>
>There is a perceived elegance aspect.
>There is also a practical aspect the only known working and 
>conveniently physically accessible ports are USB.

USB-Ethernet dongles would be a lot more useful in the long term than 
USB-Serial dongles. RS-232 had a really good 40 year run, but for 
general communications it was mostly obsolete nearly 20 years ago. You 
mentioned file transfers--I can't think of any applications where
that's going to be better over a pair of USB-Serial dongles than a pair 
of USB-Ethernet dongles.

Mike Stone

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#196335

On Fri, 1 Jun 2018 10:01:57 -0400
Michael Stone <mstone@debian.org> wrote:

> On Fri, Jun 01, 2018 at 04:56:32AM -0500, Richard Owlett wrote:
> >On 05/31/2018 06:58 PM, David Wright wrote:  
> >>(thanks for your link) gives an idea of the price, and in this case
> >>I can see some justification for it because they describe the
> >>electronics hidden inside the plugs (we hope).
> >>
> >>But considering that two NICs cost less than that cable, I'd need a
> >>pressing reason to purchase the cable instead.  
> >
> >There is a perceived elegance aspect.
> >There is also a practical aspect the only known working and 
> >conveniently physically accessible ports are USB.  
> 
> USB-Ethernet dongles would be a lot more useful in the long term than 
> USB-Serial dongles. RS-232 had a really good 40 year run, but for 
> general communications it was mostly obsolete nearly 20 years ago.
> You mentioned file transfers--I can't think of any applications where
> that's going to be better over a pair of USB-Serial dongles than a
> pair of USB-Ethernet dongles.
> 
>
Radio? This gadget:

https://www.lensadaptor.com/mtf-effect-control-unit-3-kit

 uses straight point-to-point 8-bit serial over Zigbee type RF
tranceivers. Bluetooth is basically 8-bit serial over radio, though
with a very short range.

-- 
Joe
https://en.wikipedia.org/wiki/Zigbee

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#196338

On 06/01/2018 09:01 AM, Michael Stone wrote:
> On Fri, Jun 01, 2018 at 04:56:32AM -0500, Richard Owlett wrote:
>> On 05/31/2018 06:58 PM, David Wright wrote:
>>> (thanks for your link) gives an idea of the price, and in this case I
>>> can see some justification for it because they describe the
>>> electronics hidden inside the plugs (we hope).
>>>
>>> But considering that two NICs cost less than that cable, I'd need a
>>> pressing reason to purchase the cable instead.
>>
>> There is a perceived elegance aspect.
>> There is also a practical aspect the only known working and 
8>> conveniently physically accessible ports are USB.
> 
> USB-Ethernet dongles would be a lot more useful in the long term than 
> USB-Serial dongles.

*WHO* said anything about a "USB-Serial dongle"?
I want a USB-USB object. Subtle, but important, distinction.



> RS-232 had a really good 40 year run, but for 
> general communications it was mostly obsolete nearly 20 years ago. You 
> mentioned file transfers-

So what?
I get grief for not mentioning immediate goals.
I casually mention a potential use and get *UNIVERSAL ADVICE*:
     Don't do that. <ROFL>!


-I can't think of any applications where
> that's going to be better over a pair of USB-Serial dongles than a pair 
> of USB-Ethernet dongles.

Please read my stated goals.
Not my PREsumed goals.
*ROFL*

> 
> Mike Stone
> 

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#196340

Richard,

On Fri, Jun 01, 2018 at 02:16:47PM -0500, Richard Owlett wrote:
> On 06/01/2018 09:01 AM, Michael Stone wrote:
> >I can't think of any applications where that's going to be better
> >over a pair of USB-Serial dongles than a pair of USB-Ethernet
> >dongles.
> 
> Please read my stated goals.
> Not my PREsumed goals.
> *ROFL*

Laugh all you want at people trying to help you, but time and time
again you end up posting volumes of text here without finding a
solution because you suck at concisely describing what you want to
achieve. Everyone else fails to understand you, every time, so is
everyone just stupid, or is it that the common factor here is you?

Your first email said you wanted your machines to "communicate".
That's as specific as you got.

Dan then tried to narrow it down to one specific form of
communication by spending a lot of their time listing out everything
they could think of that you might have meant, and you replied,
"Your list pretty much covers it." Useless and frustrating.

Then Stefan tried:

> > What kind of "communicate" do you need there?

Your response?

> Essentially any :/

I don't know what kind of response you expect to that uselessly
vague comment. By doing that you force people to spend a lot of
their time trying to cover every base, and then you complain at them
when they try. It really seems like you just want to complain when
people try their best to help you, even against your best efforts.

I expect to just get a barrel of whinging back for this, but I hate
to write a totally useless email myself, so…

You mentioned you want to transfer files.

If both machines have Ethernet interfaces then (as you've already
been advised) the simplest, most reliable and most performant way
will be direct Ethernet connection, or connection via a switch. If
file transfer is your goal, no need to bother with USB.

If somehow these machines don't both have Ethernet and USB really is
the only way, then again as you've already been advised, USB
Ethernet is the way to go.

We are now leaving the realms of simplicity and performance for more
subjective lands of doing things "just because" or for the retro
computing experience. You can certainly use a pair of USB serial adaptors
and then run a null modem cable between them, then run PPP over
that. Absolutely no idea why you would want to do this rather than
run Ethernet over USB. Instead of PPP you could use more arcane
forms of serial data transfer like zmodem or kermit.

If it's just a console you want, i.e. the console output and login
prompt from one machine to appear in a serial terminal program on
the other, then you can do that over Ethernet too! See "netconsole".

For a serial console when you don't have Ethernet (or want it
separate from the Ethernet infrastructure) then again it's USB
serial dongles on both ends, a null modem cable in between, then use
a serial terminal emulator like minicom or screen on the end you
want to be the client. There are configuration details involved for
the server end to get it to send console output to this USB-serial,
and put a login prompt on it.

Ask which parts you need more info on. Please be specific. Please
don't make this harder than it needs to be!

Cheers,
Andy

-- 
https://bitfolk.com/ -- No-nonsense VPS hosting

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#196342

On Fri, Jun 01, 2018 at 02:16:47PM -0500, Richard Owlett wrote:
>>USB-Ethernet dongles would be a lot more useful in the long term 
>>than USB-Serial dongles.
>
>*WHO* said anything about a "USB-Serial dongle"?
>I want a USB-USB object. Subtle, but important, distinction.

Well, you started out talking about RS232 and null modem cables, so 
don't be surprised if people are having trouble figuring out what you're 
asking for. Then you asked for better ideas. Then you got mad about all 
the ideas and started laughing hysterically. I have no idea what you 
actually want at this point.

>>RS-232 had a really good 40 year run, but for general communications 
>>it was mostly obsolete nearly 20 years ago. You mentioned file 
>>transfers-
>
>So what?
>I get grief for not mentioning immediate goals.
>I casually mention a potential use and get *UNIVERSAL ADVICE*:
>    Don't do that. <ROFL>!

So you can't articulate what you're trying to do at all? That will 
certainly reduce the odds of getting helpful advice.

It seems like you want to connect two computers via USB "just because". 
Good luck with that.

Mike Stone

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#196310

> I have two computers with USB ports.
> I wish them to communicate as simply as mid-20th-century computers did.

What kind of "communicate" do you need there?

The "way back machine" to simulate a "null modem" serial cable exists,
as you've seen, but it's rarely the best solution for nowadays's needs,
since nowadays connecting two computers is something completely normal,
supported by a deluge of tools, but they all expect a "network"
connection rather than a serial cable.

In most cases those two computers also have ethernet or wifi "ports" so
you can connect them via such a network (which usually offers faster
transmission than a serial cable, lets you seamlessly multiplex several
connections, and lets you use the many tools working over the network to
connect computers).

In some cases one of the two computers's USB port is an "OTG" port,
meaning that it can act either as "master" or not, in which case you can
just use a regular USB cable (and usually you then configure the OTG
side to pretend it's a network card, so it ends up looking to the
software like you've connected the two machines via an ethernet cable.
That's what I use between my BananaPi "router" and my office desktop).

If none of that are options, you can resort to using an "ethernet
dongle" on both sides and an ethernet cable between the two.

All of those things will typically work "out of the box" on a vanilla
Linux kernel (the usbnet drivers have been incorporated years ago).

Oh, and in case those computers are somewhat old, they may also come
with Firewire ports, and those (contrary to USB) don't have the
"slave/master" distinction so you can connect your computers this way
with a plain normal Firewire cable (and make it appear to the software,
again, as some kind of ethernet-like connection).


        Stefan

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#196311

> If none of that are options, you can resort to using an "ethernet
> dongle" on both sides and an ethernet cable between the two.

[ If one of the two computers has a free ethernet port, you can of
  course also such a dongle on the other computer.  ]

BTW, those ethernet dongles can be found pretty cheaply (like $10 or
less) and they can be handy in many cases to add an ethernet port (or
several ports, even).  IOW, it's a good tool to have in your box.


        Stefan

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