Adafruit Trinket M0


The Adafruit Trinket M0 is a tiny (27 mm x 15 mm) ARM development board with an onboard RGB LED, USB port, and range of I/O broken out onto 5 pins.

Adafruit Trinket M0


  • ATSAMD21E18A ARM Cortex-M0+ processor at 48 MHz
  • 256 KiB flash memory and 32 KiB of RAM
  • Internal trimmed 8 MHz oscillator
  • A user LED
  • An RGB DotStar LED
  • Native USB port
  • One reset button

Supported Features

The adafruit_trinket_m0 board configuration supports the following hardware features:

Interface Controller Driver/Component
NVIC on-chip nested vector interrupt controller
Flash on-chip Can be used with NFFS to store files
SYSTICK on-chip systick
WDT on-chip Watchdog
GPIO on-chip I/O ports
USART on-chip Serial ports
SPI on-chip Serial Peripheral Interface ports
USB on-chip USB device

Other hardware features are not currently supported by Zephyr.

The default configuration can be found in the Kconfig file boards/arm/adafruit_trinket_m0/adafruit_trinket_m0_defconfig.

Connections and IOs

The Adafruit Trinket M0 Learn site [1] has detailed information about the board including pinouts [2] and the schematic [3].

System Clock

The SAMD21 MCU is configured to use the 8 MHz internal oscillator with the on-chip PLL generating the 48 MHz system clock. The internal APB and GCLK unit are set up in the same way as the upstream Arduino libraries.

Serial Port

The SAMD21 MCU has 6 SERCOM based USARTs. On the Trinket, SERCOM0 is the Zephyr console and is available on pins 3 (RX) and 4 (TX). SERCOM2 is available on pins 2 (RX) and 0 (TX).

SPI Port

The SAMD21 MCU has 6 SERCOM based SPIs. On the Trinket, SERCOM1 is used to drive the DotStar RGB LED. SERCOM0 can be put into SPI mode and used to connect to devices over pin 2 (MISO), pin 4 (MOSI), and pin 3 (SCK).

USB Device Port

The SAMD21 MCU has a USB device port that can be used to communicate with a host PC. See the USB Samples sample applications for more, such as the USB CDC ACM Sample Application sample which sets up a virtual serial port that echos characters back to the host PC.

Programming and Debugging

The Trinket M0 ships the BOSSA compatible UF2 bootloader. The bootloader can be entered by quickly tapping the reset button twice.


  1. Build the Zephyr kernel and the Hello World sample application:

    # On Linux/macOS
    cd $ZEPHYR_BASE/samples/hello_world
    mkdir build && cd build
    # On Windows
    cd %ZEPHYR_BASE%\samples\hello_world
    mkdir build & cd build
    cmake -GNinja -DBOARD=adafruit_trinket_m0 ..
  2. Connect the Trinket M0 to your host computer using USB

  3. Connect a 3.3 V USB to serial adapter to the board and to the host. See the Serial Port section above for the board’s pin connections.

  4. Run your favorite terminal program to listen for output. Under Linux the terminal should be /dev/ttyACM0. For example:

    $ minicom -D /dev/ttyACM0 -o

    The -o option tells minicom not to send the modem initialization string. Connection should be configured as follows:

    • Speed: 115200
    • Data: 8 bits
    • Parity: None
    • Stop bits: 1
  5. Tap the reset button twice quickly to enter bootloader mode

  6. Flash the image:

    # On Linux/macOS
    cd $ZEPHYR_BASE/samples/hello_world
    mkdir build && cd build
    # On Windows
    cd %ZEPHYR_BASE%\samples\hello_world
    mkdir build & cd build
    cmake -GNinja -DBOARD=adafruit_trinket_m0 ..
    ninja flash

    You should see “Hello World! arm” in your terminal.