USB "null modem" cables and related Linux driver questions

[Richard Owlett]

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

Re: USB "null modem" cables and related Linux driver questions

[Reco]

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

Re: USB "null modem" cables and related Linux driver questions

[Dan Ritter]

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-

Re: USB "null modem" cables and related Linux driver questions

[Stefan Monnier]

> 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

Re: USB "null modem" cables and related Linux driver questions

[Stefan Monnier]

> 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

Re: USB "null modem" cables and related Linux driver questions

[deloptes]

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.
> 

J., why not take a crossover cable - all pcs have now ethernet port

https://en.wikipedia.org/wiki/Ethernet_crossover_cable

Re: USB "null modem" cables and related Linux driver questions

[tomas]

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On Fri, Jun 01, 2018 at 08:27:13AM +0200, deloptes wrote:
> 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.
> > 
> 
> J., why not take a crossover cable - all pcs have now ethernet port

FWIW these days, most devices are capable of doing the crossover thing
automatically [1], so you can just use a straight cable. From personal
experience, I haven't needed a crossover cable the last ten years (and
I do muck around with oldish hardware).

Cheers

[1] https://en.wikipedia.org/wiki/Medium_Dependent_Interface#Auto_MDI-X

- -- tomás
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=tkoi
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Re: USB "null modem" cables and related Linux driver questions

[Richard Owlett]

On 05/31/2018 10:07 PM, Stefan Monnier wrote:

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?


Essentially any ;/
In fact one of the thought experiments I was pursuing was how to do file 
copying/sharing over RS232 - even I would not actually attempt to implement.




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,


"Best" is not an invariant absolute.


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).


An explicit requirement is a wired, NOT WiFi, connection.
I that seriously. My internet access is a WiFi hotspot with its WiFi 
capability disabled.




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).


I saw it and it meets most (all?) my requirements except my reading 
suggested:

  1. obsolete
  2. available only for Windows/Mac
  3. no way to determine if any of machines were equipped



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


That's a 1 versus 3 items required per connection.



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

Re: USB "null modem" cables and related Linux driver questions

[Richard Owlett]

On 06/01/2018 01:27 AM, deloptes wrote:

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.



J., why not take a crossover cable - all pcs have now ethernet port

https://en.wikipedia.org/wiki/Ethernet_crossover_cable




Some combinations require crossover cable, some don't.
I investigated that and wen so fa as to purchase a {still shrink 
wrapped} 8-port switch as a solution. Decided clutter not worth it.

Re: USB "null modem" cables and related Linux driver questions

[Stefan Monnier]

>> 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).
>
> I saw it and it meets most (all?) my requirements except my reading
> suggested:
>   1. obsolete
>   2. available only for Windows/Mac
>   3. no way to determine if any of machines were equipped

Not obsolete at all.
Availability has nothing to do with the OS (I never use either of macOS
or Windows).

But yes, OTG rare (read: non-existing) on laptops/desktops.
They're very common on "embedded systems" which are expected to be
(occasionally) plugged into a computer.  E.g. many phones's USB port
is OTG.

>> If none of that are options, you can resort to using an "ethernet
>> dongle" on both sides and an ethernet cable between the two.
> That's a 1 versus 3 items required per connection.

I just gave you alternatives.  You'll let you decide what's better for
your planned use cases.


Stefan

Re: USB "null modem" cables and related Linux driver questions

[Stefan Monnier]

> 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

Re: USB "null modem" cables and related Linux driver questions

[tomas]

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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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Re: USB "null modem" cables and related Linux driver questions

[Michael Stone]

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

Re: USB "null modem" cables and related Linux driver questions

[Richard Owlett]

On 06/01/2018 08:21 AM, to...@tuxteam.de wrote:

-BEGIN PGP SIGNED MESSAGE-
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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!



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 $ ;/

Re: USB "null modem" cables and related Linux driver questions

[David Wright]

On Fri 01 Jun 2018 at 05:26:01 (-0500), Richard Owlett wrote:
> On 06/01/2018 01:27 AM, deloptes wrote:
> >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.
> >>
> >
> >J., why not take a crossover cable - all pcs have now ethernet port
> >
> >https://en.wikipedia.org/wiki/Ethernet_crossover_cable
> >
> >
> 
> Some combinations require crossover cable, some don't.
> I investigated that and wen so fa as to purchase a {still shrink
> wrapped} 8-port switch as a solution. Decided clutter not worth it.

Just forget anyone said "crossover cable¹". You'd have to be making a
direct connection between two museum pieces to require one, and as
you have a switch, you have absolutely no need to ever do that.
Coonect both to the switch instead.

Accessibility? Using the NIC (usually at the back), it gets inserted
permanently and then forgotten, rather than needing to be inserted
on each occasion you want connectivity. Tidier too.

Bear in mind you're using the hardware as intended: no risk of
blowing up your USB port. (Ever noticed how often flaky USB ports
are mentioned here?)

You might even find you can use wakeonlan on the desktop PCs
to save some power.

¹ If you *have* obtained one, just use it like an ordinary cable nowadays.

Cheers,
David.

Re: USB "null modem" cables and related Linux driver questions

[Joe]

On Fri, 1 Jun 2018 10:01:57 -0400
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 
> >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

Re: USB "null modem" cables and related Linux driver questions

[Gene Heskett]

On Friday 01 June 2018 06:20:59 Richard Owlett wrote:

> On 05/31/2018 10:07 PM, Stefan Monnier wrote:
> >> 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?
>
> Essentially any ;/
> In fact one of the thought experiments I was pursuing was how to do
> file copying/sharing over RS232 - even I would not actually attempt to
> implement.

Other than speed of the copy while the error correction verify's it 
sector by sector, why not. Both rsync and rzsz are quite capable of 
sending a file halfway around the planet with the last 17 miles on a 
barbed wire fence. And getting identical crc's in the final check.

For a circuit that was actually that dirty, I think I'd choose rzsz as 
its default packet size is 256 bytes.  If the crc of that packet fails, 
it requests a resend until it gets it right. So does rsync, but rsync's 
default packet is 64k, demanding a far cleaner path. rzsz unforch has 
several cousins 3x removed, so there is less than 100% compatibility. 
And the linux version is one of the worse compatibility violators.

> > 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,
>
> "Best" is not an invariant absolute.
>
> > 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).
>
> An explicit requirement is a wired, NOT WiFi, connection.
> I that seriously. My internet access is a WiFi hotspot with its WiFi
> capability disabled.
>
> > 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).
>
> I saw it and it meets most (all?) my requirements except my reading
> suggested:
>1. obsolete
>2. available only for Windows/Mac
>3. no way to determine if any of machines were equipped
>
> > If none of that are options, you can resort to using an "ethernet
> > dongle" on both sides and an ethernet cable between the two.
>
> That's a 1 versus 3 items required per connection.
>
> > 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



-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

Re: USB "null modem" cables and related Linux driver questions

[Richard Owlett]

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. !


-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

Re: USB "null modem" cables and related Linux driver questions

[Andy Smith]

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

Re: USB "null modem" cables and related Linux driver questions

[Michael Stone]

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. !


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

Re: USB "null modem" cables and related Linux driver questions

[David Wright]

On Fri 01 Jun 2018 at 09:08:53 (-0500), Richard Owlett wrote:
> On 06/01/2018 08:21 AM, to...@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.

Re: USB "null modem" cables and related Linux driver questions

[Joe Pfeiffer]

Richard Owlett  writes:

> On 06/01/2018 08:21 AM, to...@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.

Re: USB "null modem" cables and related Linux driver questions

[Joe Pfeiffer]

Richard Owlett  writes:

> 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].

Given how FTDI does things, I'd be really surprised if this didn't meet
your desires.  Have you actually tried it?  Are you sure there is no
driver in the kernel?

As for your actual needs...  if you want two computers to communicate,
you really ought to be using some sort of networking hardware.  You've
got a computer with a USB port, no serial port, and no ethernet or wifi?

Re: USB "null modem" cables and related Linux driver questions

[Tixy]

On Wed, 2018-06-06 at 22:26 -0600, Joe Pfeiffer wrote:
> Richard Owlett  writes:
> 
> > 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].
> 
> Given how FTDI does things, I'd be really surprised if this didn't
> meet
> your desires.  Have you actually tried it?  Are you sure there is no
> driver in the kernel?

There is a driver in Linux because, from what the datasheet says, that
cable is two of FTDIs standard USB-to-serial chips wired together. I.e.
it's equivalent to getting 2 USB to serial cables and connecting them
with a null modem cable.

-- 
Tixy

Re: USB "null modem" cables and related Linux driver questions

[Curt]

On 2018-06-07, Joe Pfeiffer  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.

Re: USB "null modem" cables and related Linux driver questions

[Michael Stone]

On Thu, Jun 07, 2018 at 08:07:15AM +0100, Tixy wrote:

On Wed, 2018-06-06 at 22:26 -0600, Joe Pfeiffer wrote:

Richard Owlett  writes:

> 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].

Given how FTDI does things, I'd be really surprised if this didn't
meet
your desires.  Have you actually tried it?  Are you sure there is no
driver in the kernel?


There is a driver in Linux because, from what the datasheet says, that
cable is two of FTDIs standard USB-to-serial chips wired together. I.e.
it's equivalent to getting 2 USB to serial cables and connecting them
with a null modem cable.


Yes, that's right. I have no idea why someone would want to do that, but 
that's exactly what it is.


There are also usb transfer cables which are basically a proprietary 
FIFO buffer with a usb master on both sides, which allow higher speed 
networking.  (Which at least seems more useful than going through a 
RS-232 conversion, but much more limited than an actual network. In some 
cases where you want more than gigabit speeds and will never have more 
than two computers it might be useful. I'm not sure how many of them can 
connect machines with different OSs, either. This is the "laplink" style 
connection.)


If you want a true, standardized, network session over your peripheral 
connection, then get firewire. (This is what not having a bus master 
allows.) It'll be old hardware, because it turns out that nobody 
actually wanted to pay more so that every device could be a master, and 
so firewire died. But once upon a time, this was one of its big 
advantages over usb.


Mike Stone

Re: USB "null modem" cables and related Linux driver questions

[David]

On 1 June 2018 at 00:21, Richard Owlett  wrote:
>
> I have two computers with USB ports.
> I wish them to communicate as simply as mid-20th-century computers did.

What is the make and model number of each computer?

Re: USB "null modem" cables and related Linux driver questions

[Michael Stone]

On Mon, Jun 18, 2018 at 10:17:21PM +1000, David wrote:

On 1 June 2018 at 00:21, Richard Owlett  wrote:


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


What is the make and model number of each computer?


He really doesn't want a sensible solution, just let it go.

Re: USB "null modem" cables and related Linux driver questions

[Richard Owlett]

On 06/18/2018 07:17 AM, David wrote:

On 1 June 2018 at 00:21, Richard Owlett  wrote:


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


What is the make and model number of each computer?


No longer a relevant question.
I have purchased a cable based on the Prolific PL-25A1 chipset.
Current kernels can make it look like an Ethernet connection.
Once I finish some configuration homework {primary motivation has 
shifted to education} I'll be able to have a client-server setup.

Re: USB "null modem" cables and related Linux driver questions

[rhkramer]

On Monday, June 18, 2018 08:44:20 AM Michael Stone wrote:
> He really doesn't want a sensible solution, just let it go.

+1