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Re: Serial Port Issues

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Thanks for all the help.

Chris

On Mon, Apr 6, 2020 at 11:59 PM Chris Rhodin <cprhodin@gmail.com> wrote:

> I figured it out.  It was user error.  When I diff'd the output of "stty"
> from my laptop and server I saw the server had "-crtscts" and laptop had
> "crtscts".  It turns out minicom enables hardware flow control by default
> and I had changed that default on my laptop somewhere in the past (at least
> 3 releases of Debain ago).  I thought I had checked this on the server but
> either I didn't or I just missed it.  Changing this in minicom made it work.
>
> Chris
>
>
> On Mon, Apr 6, 2020 at 10:53 PM Chris Rhodin <cprhodin@gmail.com> wrote:
>
>>
>>
>> ---------- Forwarded message ---------
>> From: Chris Rhodin <cprhodin@gmail.com>
>> Date: Mon, Apr 6, 2020 at 7:28 PM
>> Subject: Re: Serial Port Issues
>> To: <tomas@tuxteam.de>
>>
>>
>> I have two devices I'm trying to connect to, a UPS and a network switch.
>> By default the UPS runs at 2400 baud and the switch runs at 9600 baud.
>> Before connecting them to the server I verified the devices were working on
>> a laptop running Debian.  When I attached them to the server and powered
>> them up (with minicom already running) I saw the expected startup messages
>> being output by both devices (this is why I say I can receive serial
>> data).  I then started typing commands and but got no response.
>>
>> I started debugging.  I tried other cables, I tried USB to serial cables,
>> I reattached the devices to the laptop to verify they hadn't spontaneously
>> and simultaneously stopped working.  Next I simplified my test setup.  I
>> made a loop back cable that connects Tx to Rx.  I tested this cable on the
>> laptop and verified it echoed everything I typed.  On the server no echo.
>>
>> Based on responses here I've verified the permissions and tried running
>> as root.  I've also checked the flow control as reported by minicom.
>>
>> Q: Is "stty" the right command line tool to check all of a serial ports
>> settings?
>>
>> And finally, last night I burned a Debian live DVD and booted the server
>> with it.  After installing the proprietary network drivers and minicom I
>> tried the serial ports again with the same results.
>>
>> Tonight I'll look at the serial port ioctls and see if I can spot a
>> difference there.  I also try enabling flow control and fiddling with the
>> signals to see if that unstops it.
>>
>> ChrisR
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>> On Mon, Apr 6, 2020 at 7:08 AM <tomas@tuxteam.de> wrote:
>>
>>> On Mon, Apr 06, 2020 at 09:51:15AM -0400, rhkramer@gmail.com wrote:
>>> > On Monday, April 06, 2020 03:50:59 AM tomas@tuxteam.de wrote:
>>> > > Besides, a wrong baud rate would much less explain that writing is
>>> > > possible, but reading isn't. Not for classical "serials" (i.e.
>>> RS-232).
>>> >
>>> > From the OP: " On this system a serial port can only receive data and
>>> not
>>> > transmit."
>>> >
>>> > Wouldn't that mean that (from the perspective of a program running on
>>> the OP's
>>> > computer) that the serial port can read but not write?
>>>
>>> My recollection is the other way around: write but not read.
>>> But hey, I'm old and that.
>>>
>>> That (and the fact that another serial over USB showed the same
>>> symptoms) prompted me to (reluctantly) hint at permissions [1],
>>> since, to my knowledge, a honest serial port cannot be configured
>>> to different send and receive speeds. But this seems to be ruled
>>> out.
>>>
>>> Another possibility is, of course, the cable :-)
>>>
>>> Do we know in which way the port fails to read/write or whatever
>>> it fails at? Error messages?
>>>
>>> Cheers
>>> [1] this could be explained by a broken udev script setting
>>>    the wrong permissions -- that would, e.g. cover the USB
>>>    adapter case. It was such a nice model :-)
>>> -- t
>>>
>>

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Thread

Re: Serial Port Issues Chris Rhodin <cprhodin@gmail.com> - 2020-04-06 07:30 +0200
  Re: Serial Port Issues deloptes <deloptes@gmail.com> - 2020-04-06 09:00 +0200
    Re: Serial Port Issues Joe <joe@jretrading.com> - 2020-04-06 09:40 +0200
      Re: Serial Port Issues <tomas@tuxteam.de> - 2020-04-06 10:00 +0200
        Re: Serial Port Issues deloptes <deloptes@gmail.com> - 2020-04-06 10:10 +0200
        Re: Serial Port Issues rhkramer@gmail.com - 2020-04-06 16:00 +0200
          Re: Serial Port Issues <tomas@tuxteam.de> - 2020-04-06 16:10 +0200
            Fwd: Serial Port Issues Chris Rhodin <cprhodin@gmail.com> - 2020-04-07 08:00 +0200
              Re: Fwd: Serial Port Issues deloptes <deloptes@gmail.com> - 2020-04-07 08:50 +0200
                Re: Fwd: Serial Port Issues "Martin McCormick" <martin.m@suddenlink.net> - 2020-04-07 15:30 +0200
                Re: Serial Port Issues Joe <joe@jretrading.com> - 2020-04-07 18:50 +0200
              Re: Serial Port Issues Chris Rhodin <cprhodin@gmail.com> - 2020-04-07 09:00 +0200
                Re: Serial Port Issues <tomas@tuxteam.de> - 2020-04-07 09:10 +0200
                Re: Serial Port Issues Chris Rhodin <cprhodin@gmail.com> - 2020-04-07 09:10 +0200
                Re: Serial Port Issues songbird <songbird@anthive.com> - 2020-04-08 13:50 +0200
              Re: Serial Port Issues Joe <joe@jretrading.com> - 2020-04-07 09:30 +0200
      Re: Serial Port Issues Greg Wooledge <wooledg@eeg.ccf.org> - 2020-04-06 14:40 +0200
        Re: Serial Port Issues Joe <joe@jretrading.com> - 2020-04-06 15:30 +0200

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