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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").

USB Serial Console Alternative

For general terminal access over USB (not early boot debugging), see the USB Serial Console section in the USB Networking guide. The USB serial console runs at the same 1500000 baud and appears as /dev/ttyACM0 on Linux hosts.

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 prefer 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 default 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.