Atmel SAM L21 Xplained Pro

Support for the Atmel SAM L21 Xplained Pro board. More...

Detailed Description

Support for the Atmel SAM L21 Xplained Pro board.


The SAML21 Xplained Pro is an ultra-low power evaluation board by Atmel featuring a ATSAML21J18A SoC. The SoC includes a SAML21 ARM Cortex-M0+ micro- controller. For programming the MCU comes with 32Kb of RAM and 256Kb of flash memory.

The saml21-xpro is available from various hardware vendors for ~50USD (as of oct. 2015).

Please note:* ATMEL's most recent SAML21s are the B variant, or ATSAML21J18B. Because the driver changes are mostly small, throughout this reference the device will continue to be referred to as the ATSAML21J18[A/B] indiscriminately;


saml21-xpro image


Family ARM Cortex-M0+
Vendor Atmel
RAM 32Kb
Flash 256Kb
Frequency up to 48MHz
FPU no
Timers 8 (16-bit)
ADCs 1x 12-bit (20 channels)
UARTs max 6 (shared with SPI and I2C)
SPIs max 6 (see UART)
I2Cs max 6 (see UART)
Vcc 1.8V - 3.6V
Datasheet Datasheet
Board Manual Board Manual

User Interface

1 User button and 1 LED:

Device PIN
SW0 (button) PA02

Implementation Status

Device ID Supported Comments
MCU saml21 partly PLL clock not implemented
Low-level driver GPIO yes
PWM no
UART yes
I2C yes
SPI yes
USB no
RTT yes
RTC yes
RNG no
Timer yes
ADC yes

Flashing the device

Connect the device to your Micro-USB cable using the port labeled as EDBG.

The standard method for flashing RIOT to the saml21-xpro is using OpenOCD. Please note that even the latest official OpenOCD (v0.9 at the time of this writing) does not support B-variant SAML21 devices.

If you attempt to flash a board, and OpenOCD throws a Couldn't find part corresponding to DID XXXXXXXX error, you will need to compile your own OpenOCD from source.

Refer to for general instructions on building OpenOCD and make sure "cmsis-dap" and "hidapi-libusb" are enabled.

On Linux you will have to add a udev rule for hidraw, like

echo 'KERNEL=="hidraw*", SUBSYSTEM=="hidraw", MODE="0664", GROUP="plugdev"' \
| sudo tee -a /etc/udev/rules.d/99-usb.rules
sudo service udev restart

Arch Linux

With yaourt:

yaourt -S hidapi-git
yaourt -S openocd-git
# edit PKGBUILD, add "cmsis-dap hidapi-libusb" to "_features"


Although this refers to setting up the SAMR21, this guide is still very helpful to understanding how to set up a solid RIOT development environment for the SAML21:

Supported Toolchains

For using the saml21-xpro board we strongly recommend the usage of the GNU Tools for ARM Embedded Processors toolchain.

Known Issues / Problems

Stack sizes

The default stack sizes have not been tuned properly yet. If in doubt why your application crashes try increasing the default stack sizes and use ps to find out how much stack is being used. Tracked in

Not flashable by OpenOCD anymore

It can happen that OpenOCD is not able to program the board, because of wrong clock configuration or low power modes. In this case you can use this little tool to erase the flash. Just follow the instructions to build it and run ./edbg -e to erase the flash. Then press the reset button and you're able to program via OpenOCD again.


file  arduino_iomap.h
 Mapping from board pins to Arduino pins.
file  board.h
 Board specific definitions for the Atmel SAM L21 Xplained Pro board.
file  gpio_params.h
 Board specific configuration of direct mapped GPIOs.
file  periph_conf.h
 Peripheral MCU configuration for the Atmel SAM L21 Xplained Pro board.