---------- Forwarded message --------- From: Chris Rhodin <cprho...@gmail.com> Date: Mon, Apr 6, 2020 at 7:28 PM Subject: Re: Serial Port Issues To: <to...@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 <to...@tuxteam.de> wrote: > On Mon, Apr 06, 2020 at 09:51:15AM -0400, rhkra...@gmail.com wrote: > > On Monday, April 06, 2020 03:50:59 AM to...@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 >
