Serial Port Tools on Linux

Posted on May 28, 2019 | uart

This page lists a set of tips that I have collected over the years using serial port for interacting with embedded boards.

Minicom #

  1. Use minicom -w to start minicom with line wrapping enabled.

  2. Add yourself to the ‘dialout’ group to open Serial ports without using sudo. Remember to logout and login for the newly added group membership to take effect.

    $ sudo adduser vmandela dialout

  3. Use minicom -C log.txt to the UART port output.

  4. Hit Ctrl+a,N to toggle timestamps in minicom. I normally use GrabSerial instead if I need timing information from uart logs.

Minicom config files #

  1. The system wide configuration file for minicom is in /etc/minicom/minirc.dfl. You can override the system configuration by creating a config file at ~/.minirc.dfl.

  2. To open a specific port by name(say usb0), create a file ~/.minirc.usb0 and include all the required configuration parameters in it.

    $ cat ~/.minirc.usb0
pu port             /dev/ttyUSB0
pu baudrate         115200
pu bits             8
pu parity           N
pu stopbits         1

    Now you can open /dev/ttyUSB0 by doing

    $ minicom usb0

    instead of

    $ minicom -D /dev/ttyUSB0

Use Byobu for multiple serial ports #

For boards which have multiple UART outputs, I use byobu + tmux to open all the UART ports in one command. The boards usually have multiple UART’s multiplexed on to a single USB port using an FTDI chip.

$ cat ~/.byobu/windows.tmux.evm1
new-session -n port0 -c /home/vmandela/work/ minicom -c on -w -C port0.txt usb0;
new-window -n port1 -c /home/vmandela/work/ minicom  -c on -w -C port1.txt usb1;
new-window -n port2 -c /home/vmandela/work/ minicom  -c on -w -C a53.txt usb2;
rename-session EVM1-UART
$ BYOBU_WINDOWS=evm1 byobu

GrabSerial #

Grabserial is an amazing tool for capturing and timestamping UART logs. I used it extensively when performing boot time optimizations. Grabserial provides a running time stamp as well as delta from the previous line. This makes it easy to identify functionality consuming most time.

You can install grabserial from ubuntu repositories.

$ sudo apt install grabserial

It is also available in the NixOS repositories.

$ nix-env -iA nixpkgs.grabserial

The below command captures logs from ttyUSB5 until 120 seconds or receiving the string “test(s)”

$ grabserial -d /dev/ttyUSB5 -q 'test\(s\)' -e 120 | tee /home/vmandela/work/usb5.txt

Add the -t command line option to enable timestamping.

XModem File transfer #

One of the issues with minicom is the lack of scripting facilities. On Windows, TeraTerm offers scripting with its own TTL language. I did not find a viable alternative on Linux yet and had to use python to automate booting of an board over UART. Here is a python script that boots a AM6 EVM over UART. The script is based on the example at xmodem pypi page.

#!/usr/bin/env python
import serial
import sys
from xmodem import XMODEM
import logging
import subprocess

# Uncomment for logs on XMODEM block transfer
# logging.basicConfig(level=logging.DEBUG)

uart_port='/dev/ttyUSB5'
print "Port used is " + uart_port

bin_loc='test.bin'
port = serial.Serial(uart_port,
                     115200, timeout=1) # or whatever port you need

def getc(size, timeout=1):
    return port.read(size) or None

def putc(data, timeout=1):
    return port.write(data)  # note that this ignores the timeout

modem = XMODEM(getc, putc)

# Wait for character indicating the EVM is ready to receive the binary
print "Waiting for C"
rcv = 'd'
while rcv != 'C':
    rcv = port.read(1)
    if rcv:
        print rcv

print "Sending file"
bin = open(bin_loc, 'rb')
modem.send(bin)
bin.close()
port.close()

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