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Fwd: Serial Port Issues

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---------- 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






















































































....0

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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