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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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#196322

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
> 
> 

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#196325

>> 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

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#196334

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 <http://geneslinuxbox.net:6309/gene>

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#196314

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

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#196316

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Hash: SHA1

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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#196320

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.

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#196329

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.

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#196457

Richard Owlett <rowlett@cloud85.net> 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?

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#196459

On Wed, 2018-06-06 at 22:26 -0600, Joe Pfeiffer wrote:
> Richard Owlett <rowlett@cloud85.net> 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

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#196468

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 <rowlett@cloud85.net> 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

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#196748

On 1 June 2018 at 00:21, Richard Owlett <rowlett@cloud85.net> 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?

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#196750

On Mon, Jun 18, 2018 at 10:17:21PM +1000, David wrote:
>On 1 June 2018 at 00:21, Richard Owlett <rowlett@cloud85.net> 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.

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#196753

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

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#196752

On 06/18/2018 07:17 AM, David wrote:
> On 1 June 2018 at 00:21, Richard Owlett <rowlett@cloud85.net> 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.

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