Seeeduino XIAO

Overview

The Seeeduino XIAO is a tiny (20 mm x 17.5 mm) ARM development board with onboard LEDs, USB port, and range of I/O broken out onto 14 pins.

Hardware

  • ATSAMD21G18A ARM Cortex-M0+ processor at 48 MHz

  • 256 KiB flash memory and 32 KiB of RAM

  • Three user LEDs

  • Native USB port

Supported Features

The seeeduino_xiao board configuration supports the following hardware features:

Interface

Controller

Driver/Component

DMA

on-chip

Direct memory access

DAC

on-chip

Digital to analogue converter

Flash

on-chip

Can be used with LittleFS to store files

GPIO

on-chip

I/O ports

HWINFO

on-chip

Hardware info

I2C

on-chip

Inter-Integrated Circuit

NVIC

on-chip

nested vector interrupt controller

SPI

on-chip

Serial Peripheral Interface ports

SYSTICK

on-chip

systick

USART

on-chip

Serial ports

USB

on-chip

USB device

WDT

on-chip

Watchdog

Other hardware features are not currently supported by Zephyr.

The default configuration can be found in the Kconfig file boards/seeed/seeeduino_xiao/seeeduino_xiao_defconfig.

Connections and IOs

The Seeeduino XIAO wiki [1] has detailed information about the board including pinouts [2] and the schematic [3].

System Clock

The SAMD21 MCU is configured to use the 32 kHz external crystal 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.

SPI Port

The SAMD21 MCU has 6 SERCOM based SPIs. On the XIAO, SERCOM0 can be put into SPI mode and used to connect to devices over pin 9 (MISO), pin 10 (MOSI), and pin 8 (SCK).

I2C Port

The SAMD21 MCU has 6 SERCOM based USARTs. On the XIAO, SERCOM2 is available on pin 4 (SDA) and pin 5 (SCL).

Serial Port

The SAMD21 MCU has 6 SERCOM based USARTs. On the XIAO, SERCOM4 is the Zephyr console and is available on pins 7 (RX) and 6 (TX).

USB Device Port

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

DAC

The SAMD21 MCU has a single channel DAC with 10 bits of resolution. On the XIAO, the DAC is available on pin 0.

Programming and Debugging

The XIAO ships the BOSSA compatible UF2 bootloader. The bootloader can be entered by shorting the RST and GND pads twice.

Additionally, if CONFIG_USB_CDC_ACM is enabled then the bootloader will be entered automatically when you run west flash.

Flashing

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

    west build -b seeeduino_xiao samples/hello_world

  2. Connect the XIAO 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/ttyUSB0. For example:

    $ minicom -D /dev/ttyUSB0 -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. Short the RST and GND pads twice quickly to enter bootloader mode

  6. Flash the image:

    west build -b seeeduino_xiao samples/hello_world
west flash

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

References