Linux: Selecting The Right Serial Port

 Computing, Linux  No Responses »
Jun 222020
 

I have a problem with serial ports (usually “virtual ones” or USB←→serial port dongles) – I have too many of them, and I usually end up with the wrong one. And selecting a TrueRNG serial port and connecting a terminal emulator to it gets very messy very quickly.

So I was searching around, semi-idly wondering if I could somehow build a device name to USB name mapping that I could stuff into rofi (or dmenu) and I discovered the /dev/serial/by-id/ which did 99% of the work for me.

So yes, I can invoke kermit and up will pop a menu allowing me to select which serial port to connect to :-

ls /dev/serial/by-id |\
  rofi -dmenu -l 20 -p "Pick a serial device" -font "mono 20"

That is the core of it, but to make it functional I need to embed it into a command line argument to kermit :-

alias kermit='kermit -C "set line /dev/serial/by-id/$(ls /dev/serial/by-id | rofi -dmenu -l 20 -p "Pick a serial device" -font "mono 20"),set carrier-watch off"'

Which is admittedly a bit of a mouthful!

But so useful if you have two or three USB to serial adopters plugged in plus a switch’s console port and a Linux widget that provides a serial console.

Building Kermit

 Computing, Linux  No Responses »
Jun 222020
 

Unfortunately, the serial communication program I tend to use (kermit) appears to have not been updated in quite a while. Which in some ways is reasonable (it’s a very old program and probably does not need much work), understandable (the main developer is no longer employed to make it work), but is somewhat frustrating when it no longer compiles.

To get it to work on my latest system :-

  1. Download the cku302.tar.gz source code and unpack.
  2. Try the first compile with make linux KFLAGS=-DNOARROWKEYS (losing the arrow keys is unfortunate but not fatal unless you’re in command mode far too long).
  3. If that doesn’t compile with zillions of undefined references to curses sounding functions (printw, stdscr, wmove, etc.) then scroll up to the top of the errors where the final command to “compile” all the objects into a final binary is available. Paste that command and add a “-lncurses” :-
$ gcc  -o wermit \
      ckcmai.o ckclib.o ckutio.o ckufio.o \
      ckcfns.o ckcfn2.o ckcfn3.o ckuxla.o \
      ckcpro.o ckucmd.o ckuus2.o ckuus3.o \
      ckuus4.o ckuus5.o ckuus6.o ckuus7.o \
      ckuusx.o ckuusy.o ckuusr.o ckucns.o \
      ckudia.o ckuscr.o ckcnet.o ckusig.o \
      ckctel.o ckcuni.o ckupty.o ckcftp.o \
      ckuath.o ck_crp.o ck_ssl.o -lutil -lresolv -lcrypt -lncurses -lm

The final output of “wermit” just needs to be stripped, moved to a proper location, and renamed :-

$ strip wermit
$ sudo mv wermit /opt/bin/kermit

And there it seems to work fine.

Of course this is not a proper fix, and we are missing a lot of features but it is at least working. And saves me from having to struggle with minicom, screen, or cu.