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

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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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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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