CIRCUITPY

CIRCUITPY is the default filename used by many Adafruit microcontroller boards to boot into the CircuitPython firmware. When a board such as the Adafruit Feather, Metro, or Trinket is powered on, the bootloader automatically mounts the internal storage block device as a USB mass storage volume and writes the firmware into a file named CIRCUITPY. This file then acts as a virtual terminal and contains a ready‑to‑use Python interpreter pre‑loaded with libraries and examples.

The CIRCUITPY volume presents a straightforward environment for rapid prototyping. Users can plug a USB cable into a PC, drag and drop Python scripts (.py files) and support modules into the root directory, and the board immediately executes them on reconnect. Changing the firmware or boot behavior is accomplished by replacing or resizing the CIRCUITPY file on the device.

CircuitPython itself is a derivative of MicroPython tailored for microcontrollers, offering simplified I/O, built‑in support for peripheral drivers, and a large community supply of open‑source libraries. The CIRCUITPY mechanism encapsulates the firmware image into a file that appears as a flash partition, eliminating the need for a separate bootloader or firmware installer. This design allows developers to focus on code rather than device configuration, and it keeps the board in a state that is consistent with the latest stable CircuitPython releases.