Platform Atmel SAM: Atmel | SMART offers Flash- based ARM products based on the ARM Cortex-M0+, Cortex-M3 and Cortex-M4 architectures, ranging from 8KB to 2MB of Flash including a rich peripheral and feature mix.

Microcontroller SAMR21G18A
Frequency 48MHz
Flash 256KB
Vendor Atmel


Please use samr21_xpro ID for board option in “platformio.ini” (Project Configuration File):

platform = atmelsam
board = samr21_xpro

You can override default Atmel ATSAMR21-XPRO settings per build environment using board_*** option, where *** is a JSON object path from board manifest samr21_xpro.json. For example, board_build.mcu, board_build.f_cpu, etc.

platform = atmelsam
board = samr21_xpro

; change microcontroller
board_build.mcu = samr21g18a

; change MCU frequency
board_build.f_cpu = 48000000L


Atmel ATSAMR21-XPRO supports the next uploading protocols:

  • atmel-ice
  • blackmagic
  • cmsis-dap
  • jlink

Default protocol is cmsis-dap

You can change upload protocol using upload_protocol option:

platform = atmelsam
board = samr21_xpro

upload_protocol = cmsis-dap


PIO Unified Debugger - “1-click” solution for debugging with a zero configuration.


You will need to install debug tool drivers depending on your system. Please click on compatible debug tool below for the further instructions and configuration information.

You can switch between debugging Tools & Debug Probes using debug_tool option in “platformio.ini” (Project Configuration File).

Atmel ATSAMR21-XPRO has on-board debug probe and IS READY for debugging. You don’t need to use/buy external debug probe.

Compatible Tools On-board Default
Black Magic Probe    


Name Description
Mbed The mbed framework The mbed SDK has been designed to provide enough hardware abstraction to be intuitive and concise, yet powerful enough to build complex projects. It is built on the low-level ARM CMSIS APIs, allowing you to code down to the metal if needed. In addition to RTOS, USB and Networking libraries, a cookbook of hundreds of reusable peripheral and module libraries have been built on top of the SDK by the mbed Developer Community.
Zephyr The Zephyr Project is a scalable real-time operating system (RTOS) supporting multiple hardware architectures, optimized for resource constrained devices, and built with safety and security in mind.