Skip to content

Serial Console Access

A hardware serial console is the most reliable way to debug early boot issues or recover a system when network access is unavailable. The Picocalc exposes a USB-to-UART bridge that enumerates as /dev/ttyUSB0 on most Linux hosts. The console runs at 1,500,000 baud, 8 data bits, no parity, and 1 stop bit ("1500000 8N1").

Prerequisites

  • Linux host with python3-serial (for miniterm.py) or minicom installed.
  • Access to /dev/ttyUSB0. If you are not root, add yourself to the dialout (or distribution-specific) group and re-login:

Info

If you prefeer a GUI tool to access the serial port but don't know what to choose, options on Linux desktops include CuteCom, and PuTTY among others; they provide point-and-click interfaces for selecting ports and baud rates. The only setting you will need to change is the 1,500,000 baud setting. 

sudo usermod -a -G dialout "$USER"
  • USB-C cable connecting the host to the Picocalc usb-c port.

Verifying the device node

After connecting the board, confirm the kernel created the serial device:

ls /dev/ttyUSB*

You should see /dev/ttyUSB0. If the device is missing, check dmesg for driver errors or verify cabling. If you already have other serial devices, it may have received a different number.

Using miniterm.py

miniterm.py ships with the pyserial package and provides a simple serial terminal.

  1. Launch the terminal with the required baud rate:
python3 -m serial.tools.miniterm /dev/ttyUSB0 1500000
  1. Interact with the console directly in the terminal window.
  2. Use Ctrl+] to open the miniterm command menu. From there you can toggle local echo (e), change settings, or quit (q).
  3. Exit with Ctrl+] followed by q.

Optional flags:

  • --raw disables line ending translations.
  • --write-log session.log records all serial traffic to a file.

Using minicom

minicom is a curses-based serial terminal that can persist configuration between sessions.

  1. Run the setup menu once to create a default profile:
sudo minicom -s
  1. In Serial port setup:
  2. Set Serial device to /dev/ttyUSB0.
  3. Set Bps/Par/Bits to 1500000 8N1.

  4. Disable both hardware (RTS/CTS) and software (XON/XOFF) flow control unless your setup requires them.

  5. Choose Save setup as dfl so future invocations reuse these settings, then Exit the configuration menu.

  6. Start minicom normally:

minicom

Key shortcuts while running:

  • Ctrl+A then Z: help and command summary.
  • Ctrl+A then O: reopen the setup menu.
  • Ctrl+A then W: toggle logging to the file defined in the configuration.
  • Ctrl+A then X: exit minicom.

Troubleshooting

  • Permission denied: ensure your user is in the correct group or run minicom with sudo. Avoid running graphical terminals as root for security reasons.
  • Garbled output: double-check the baud rate (must be 1,500,000) and make sure only one terminal program is connected to the port.
  • No output: confirm the board is powered and the USB-to-UART bridge is enumerated by the host (dmesg | tail).

With the correct baud rate and settings, the serial console provides boot logs, kernel messages, and a root shell even before networking is available.

Because this uses a hardware serial port, it will work even if no picocalc specific drivers are loaded.