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SAM R21 Xplained Pro Evaluation Kit

Overview

The SAM R21 Xplained Pro is a compact evaluation board by Atmel featuring a ATSAMR21G18A SoC. The SoC includes a SAMR21 ARM Cortex-M0+ micro-controller bundled with Atmel’s AT86RF233, a 2.4GHz IEEE802.15.4 compatible radio. The kit includes Atmel’s Embedded Debugger (EDBG), which provides a full debug interface without the need for additional hardware.

ATSAMR21-XPRO

Hardware

  • ATSAMR21G18A ARM Cortex-M0+ processor at 48 MHz

  • 32.768 kHz crystal oscillator

  • 256 KiB flash memory and 32 KiB of RAM

  • One yellow user LED

  • One mechanical user push button

  • One reset button

  • On-board USB based EDBG unit with serial console

Supported Features

The atsamr21_xpro board configuration supports the following hardware features:

Interface

Controller

Driver/Component

NVIC

on-chip

nested vector interrupt controller

SYSTICK

on-chip

systick

WDT

on-chip

Watchdog

GPIO

on-chip

I/O ports

PWM

on-chip

Pulse Width Modulation

USART

on-chip

Serial ports

SPI

on-chip

Serial Peripheral Interface ports

I2C

on-chip

I2C Peripheral Interface ports

Other hardware features are not currently supported by Zephyr.

The default configuration can be found in the Kconfig boards/arm/atsamr21_xpro/atsamr21_xpro_defconfig.

Pin Mapping

The SAM R21 Xplained Pro evaluation kit has 3 GPIO controllers. These controllers are responsible for pin muxing, input/output, pull-up, etc.

For mode details please refer to SAM R21 Family Datasheet 1 and the SAM R21 Xplained Pro Schematic 2.

ATSAMR21-XPRO-pinout

Default Zephyr Peripheral Mapping:

  • SERCOM0 USART TX : PA5

  • SERCOM0 USART RX : PA4

  • SERCOM1 I2C SDA : PA16

  • SERCOM1 I2C SCL : PA17

  • SERCOM5 SPI MISO : PB02

  • SERCOM5 SPI MOSI : PB22

  • SERCOM5 SPI SCK : PB23

  • GPIO SPI CS : PB03

  • GPIO/PWM LED0 : PA19

System Clock

The SAMR21 MCU is configured to use the 32.768 kHz external oscillator with the on-chip PLL generating the 48 MHz system clock.

Serial Port

The SAMR21 MCU has six SERCOM based USARTs with two configured as USARTs in this BSP. SERCOM0 is the default Zephyr console.

  • SERCOM0 115200 8n1 connected to the onboard Atmel Embedded Debugger (EDBG)

PWM

The SAMR21 MCU has 3 TCC based PWM units with up to 4 outputs each and a period of 24 bits or 16 bits. If CONFIG_PWM_SAM0_TCC is enabled then LED0 is driven by TCC0 instead of by GPIO.

SPI Port

The SAMR21 MCU has 6 SERCOM based SPIs.

  • SERCOM5 is exposed via Xplained Pro Standard Extension Header

I2C Port

When connecting an I2C device and a logic analyzer to an I2C port at the same time, the internal pull-up resistors are not sufficient for stable bus operation. You probably have to connect external pull-ups to both bus lines. 10K is a good value to start with.

  • SERCOM1 is exposed via Xplained Pro Standard Extension Header

Radio

The SAMR21 SoC includes an on-chip AT86RF233 radio. It is internally connected via SPI and some GPIO pins and behaves the same way as externally connected SPI devices.

Sensor

AT86RF233

Type

2.4GHz IEEE802.15.4 radio

Vendor

Atmel

Datasheet

Datasheet

connected to

SPI_0

Pin Config:

Device

SERCOM4

MOSI

PB30 (OUT, SPI MOSI)

MISO

PC19 (IN, SPI MISO)

SCLK

PC18 (OUT, SPI SCLK)

CS

PB31 (OUT, GPIO output)

IRQ

PB00 (IN, GPIO external interrupt)

RSTN

PB15 (OUT, GPIO output)

SLP_TR

PA20 (OUT, GPIO output)

Zephyr provide several samples that can use this technology. You can check wpanusb sample and 802.15.4 “serial-radio” sample examples as starting points. Another good test can be done with IPv6 by using the server/client echo demo. More information at Socket Echo Server and Socket Echo Client.

Programming and Debugging

The SAM R21 Xplained Pro comes with a Atmel Embedded Debugger (EDBG). This provides a debug interface to the SAMR21 chip and is supported by OpenOCD.

Flashing

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

    west build -b atsamr21_xpro samples/hello_world

  2. Connect the SAM R21 Xplained Pro to your host computer using the USB debug port.

  3. Run your favorite terminal program to listen for output. Under Linux the terminal should be /dev/ttyACM0. For example:

    $ minicom -D /dev/ttyACM0 -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

  4. To flash an image:

    west build -b atsamr21_xpro samples/hello_world
west flash

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