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
NVIC	on-chip	nested vector interrupt controller
SPI	on-chip	Serial Peripheral Interface ports
I2C	on-chip	Inter-Integrated Circuit
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/arm/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 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.

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

Build the Zephyr kernel and the Hello World sample application:
```
west build -b seeeduino_xiao samples/hello_world
```
Connect the XIAO to your host computer using USB
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.
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
Short the RST and GND pads twice quickly to enter bootloader mode
Flash the image:
```
west build -b seeeduino_xiao samples/hello_world
west flash
```
You should see “Hello World! seeeduino_xiao” in your terminal.