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 |
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.
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_worldConnect 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.