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USB serial ports, was: Re: Mecrisp on the TI Stellaris Launchpad

From Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP>
Newsgroups comp.arch.embedded
Subject USB serial ports, was: Re: Mecrisp on the TI Stellaris Launchpad
Date 2015-04-18 18:34 +0000
Organization A noiseless patient Spider
Message-ID <mgu844$dm6$1@dont-email.me> (permalink)
References (5 earlier) <mgq1j5$b0a$1@dont-email.me> <87h9sfwdy1.fsf@jester.gateway.pace.com> <mgrket$1d0$1@dont-email.me> <mgs7uk$75f$1@dont-email.me> <mgsemm$ans$1@dont-email.me>

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On 2015-04-17, Mel Wilson <mwilson@the-wire.com> wrote:
> On Fri, 17 Apr 2015 20:20:30 -0400, rickman wrote:
> [ ... ]
>> Even once I get a terminal emulator running, I'm not sure how to find
>> the ID of the device I'll be talking to with it.  It is a TI launchpad
>> with a USB emulated UART.  These things are like falling off a rock in
>> the PC world... mainly because I've come up the learning curve and know
>> it.  Will miniterm have the smarts to find the one serial port on the
>> machine or do I have to figure out the ID of this USB serial port and
>> tell it?
>
> What do you mean by USB emulated UART?  When I plug one of my Sparkfun 
> FTDI boards into a Pi, it shows up to lsusb as "0403:6001 Future 
> Technology Devices International, Ltd FT232 USB-Serial (UART) IC" and 
> gets assigned to /dev/ttyUSB0.
> A different device, Arduino based, announces itself as "2341:0010 Arduino 
> SA Mega 2560 (CDC ACM)" and gets assigned as /dev/ttyACM0.  This is on a 
> stock Raspbian distribution.
> The difference between the two is apparently that the FTDI emulates a 
> UART, whereas the Arduino emulates a modem, and that's somehow recognized 
> when they're establishing the USB connection.

To expand on that:

There's a standard for accessing serial ports on the USB specifications
which is the CDC ACM specification. This is fully open and documented
and many implementations exist (I did a simple version myself as a
learning exercise a few years ago).

However, as you say, it's targetted towards modems in it's model of
operation although serial ports work just fine with it. However, the
hardware flow control signals don't get directly passed through to
the host (there's no direct handling of CTS for example).

The way people like Microchip appear to handle this (in devices like
the MCP2200) is to handle the flow control on the device itself.

FTDI (and Prolific (PL-2303)) have their own closed USB protocol
specifications for their own devices. These specifications are not
available without signing an NDA (I know; in the case of FTDI I actually
asked them about this).

There are however drivers for these manufacturers in the Linux kernel
and (as you have discovered) they show up in a different way to the
standards compliant CDC ACM devices.

As for how Linux knows the difference, the different types of USB serial
ports are encoded differently in the configuration descriptors on the
device (with the CDC ACM devices using configuration values assigned
by the USB standards).

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world

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Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-02 21:08 -0400
  Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-13 16:18 -0700
    Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-13 16:25 -0700
      Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-13 16:33 -0700
        Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-13 21:45 -0400
          Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-13 21:47 -0400
            Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-14 07:33 -0700
              Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-14 14:38 -0400
    Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-16 14:24 -0700
      Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-16 15:11 -0700
        Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-16 23:37 -0400
          Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-16 20:59 -0700
            Re: Mecrisp on the TI Stellaris Launchpad Mel Wilson <mwilson@the-wire.com> - 2015-04-17 13:16 +0000
          Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 00:19 -0400
            Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-16 21:56 -0700
              Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 14:47 -0400
                WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking rickman <gnuarm@gmail.com> - 2015-04-17 15:12 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking Martin Gregorie <martin@address-in-sig.invalid> - 2015-04-17 20:14 +0000
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking rickman <gnuarm@gmail.com> - 2015-04-17 16:59 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking David Brown <david.brown@hesbynett.no> - 2015-04-18 10:00 +0200
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking rickman <gnuarm@gmail.com> - 2015-04-18 09:32 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking Martin Gregorie <martin@address-in-sig.invalid> - 2015-04-18 15:15 +0000
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking rickman <gnuarm@gmail.com> - 2015-04-18 11:31 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line   Breaking Niklas Holsti <niklas.holsti@tidorum.invalid> - 2015-04-18 19:21 +0300
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line   Breaking rickman <gnuarm@gmail.com> - 2015-04-19 16:39 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking Alan Adams <alan@adamshome.org.uk> - 2015-04-18 18:52 +0100
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-04-18 18:55 -0400
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking The Natural Philosopher <tnp@invalid.invalid> - 2015-04-19 09:13 +0100
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-19 13:22 +0300
                Re: WAS: Mecrisp on the TI Stellaris Launchpad  IS: Thunderbird Line Breaking David Brown <david.brown@hesbynett.no> - 2015-04-19 22:09 +0200
                Re: Mecrisp on the TI Stellaris Launchpad mm0fmf <none@mailinator.com> - 2015-04-17 21:15 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 17:02 -0400
                Re: Mecrisp on the TI Stellaris Launchpad mm0fmf <none@mailinator.com> - 2015-04-18 17:06 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-19 16:57 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Alan Adams <alan@adamshome.org.uk> - 2015-04-20 09:33 +0100
                Re: Mecrisp on the TI Stellaris Launchpad mm0fmf <none@mailinator.com> - 2015-04-20 18:03 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-21 01:16 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:20 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 17:24 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:40 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 17:57 -0700
                Re: Mecrisp on the TI Stellaris Launchpad Mel Wilson <mwilson@the-wire.com> - 2015-04-18 02:14 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 02:05 -0400
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 10:16 +0200
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 09:56 -0400
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 17:46 +0200
                USB serial ports, was: Re: Mecrisp on the TI Stellaris Launchpad Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2015-04-18 18:34 +0000
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 10:04 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Jan Coombs <Jan-54 <jenfhaomndgfwutc@murmic.plus.com>> - 2015-04-18 09:38 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 11:04 -0400
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 17:54 +0200
                Re: Mecrisp on the TI Stellaris Launchpad hal-usenet@ip-64-139-1-69.sjc.megapath.net (Hal Murray) - 2015-04-18 15:36 -0500
                Re: Mecrisp on the TI Stellaris Launchpad Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-04-23 07:59 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-25 14:35 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-25 15:44 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-08 12:00 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-10 03:36 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-05-10 10:32 +0100
                Re: Mecrisp on the TI Stellaris Launchpad Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-05-10 12:56 +0300
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-10 10:48 -0400
                Re: Mecrisp on the TI Stellaris Launchpad The Natural Philosopher <tnp@invalid.invalid> - 2015-05-10 16:05 +0100
                Re: Mecrisp on the TI Stellaris Launchpad Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2015-05-10 23:26 +0000
                Re: Mecrisp on the TI Stellaris Launchpad Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2015-05-10 09:37 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-10 11:16 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2015-05-10 23:42 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-11 02:17 -0400
                Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-05-10 11:41 +0000
                Re: Mecrisp on the TI Stellaris Launchpad Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-05-10 16:56 +0100
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-05-10 13:01 -0400
                Re: Mecrisp on the TI Stellaris Launchpad lasselangwadtchristensen@gmail.com - 2015-04-18 12:13 -0700
            Re: Mecrisp on the TI Stellaris Launchpad stephen@mpeforth.com (Stephen Pelc) - 2015-04-18 19:22 +0000
              Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-19 17:04 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-04-20 13:24 +0300
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 13:23 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-22 20:44 +0300
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 13:51 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2015-04-22 19:10 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 15:31 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2015-04-23 02:08 +0000
                Re: Mecrisp on the TI Stellaris Launchpad Waldek Hebisch <hebisch@math.uni.wroc.pl> - 2015-04-24 02:52 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-25 14:40 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-25 15:42 -0400
                Re: Mecrisp on the TI Stellaris Launchpad sbattazzo@gmail.com - 2015-04-21 09:34 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 14:57 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-22 15:35 -0400
          Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-17 10:52 +0000
            Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-17 14:05 +0300
            Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 07:56 -0700
              Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-17 17:26 +0200
              Re: Mecrisp on the TI Stellaris Launchpad glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-04-17 17:01 +0000
          Re: Mecrisp on the TI Stellaris Launchpad Blajrs Jrolrsen <boegre@no.com> - 2015-04-17 13:36 +0000
            Re: Mecrisp on the TI Stellaris Launchpad anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-17 14:42 +0000
              Re: Mecrisp on the TI Stellaris Launchpad Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2015-04-18 00:25 +0200
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:03 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 17:14 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:26 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-17 17:32 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 20:47 -0400
                Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-18 08:47 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 11:19 -0400
                Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-18 15:52 +0000
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-19 17:07 -0400
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-06-09 03:04 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Robert Wessel <robertwessel2@yahoo.com> - 2015-04-18 00:11 -0500
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 10:32 +0200
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-18 11:26 -0400
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 17:57 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Paul Rubin <no.email@nospam.invalid> - 2015-04-18 09:42 -0700
                Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-19 17:11 -0400
                Re: Mecrisp on the TI Stellaris Launchpad Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2015-04-18 12:19 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-18 15:16 +0300
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 19:57 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-18 23:11 +0300
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-19 21:32 +0200
                Re: Mecrisp on the TI Stellaris Launchpad Dimiter_Popoff <dp@tgi-sci.com> - 2015-04-19 23:04 +0300
                Re: Mecrisp on the TI Stellaris Launchpad anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 09:15 +0000
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 12:17 +0200
                Re: Mecrisp on the TI Stellaris Launchpad anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 13:08 +0000
                Re: Mecrisp on the TI Stellaris Launchpad David Brown <david.brown@hesbynett.no> - 2015-04-18 20:17 +0200
                Re: Mecrisp on the TI Stellaris Launchpad anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-20 15:33 +0000
            Re: Mecrisp on the TI Stellaris Launchpad rickman <gnuarm@gmail.com> - 2015-04-17 14:52 -0400
            Re: Mecrisp on the TI Stellaris Launchpad albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-17 20:06 +0000
      Re: Mecrisp on the TI Stellaris Launchpad lasselangwadtchristensen@gmail.com - 2015-04-16 16:18 -0700

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