SAM R21 Xplained Pro Evaluation Kit¶
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.
- 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
The atsamr21_xpro board configuration supports the following hardware features:
|NVIC||on-chip||nested vector interrupt controller|
|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
The SAM R21 Xplained Pro evaluation kit has 3 GPIO controllers. These controllers are responsible for pin muxing, input/output, pull-up, etc.
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 LED0 : PB17
The SAMR21 MCU is configured to use the 32.768 kHz external oscillator with the on-chip PLL generating the 48 MHz system clock.
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)
The SAMR21 MCU has 6 SERCOM based SPIs.
- SERCOM5 is exposed via Xplained Pro Standard Extension Header
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
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.
|Type||2.4GHz IEEE802.15.4 radio|
|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)|
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.
Build the Zephyr kernel and the Hello World sample application:
# On Linux/macOS cd $ZEPHYR_BASE/samples/hello_world mkdir build && cd build # On Windows cd %ZEPHYR_BASE%\samples\hello_world mkdir build & cd build cmake -GNinja -DBOARD=atsamr21_xpro .. ninja
Connect the SAM R21 Xplained Pro to your host computer using the USB debug port.
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
To flash an image:
# On Linux/macOS cd $ZEPHYR_BASE/samples/hello_world mkdir build && cd build # On Windows cd %ZEPHYR_BASE%\samples\hello_world mkdir build & cd build cmake -GNinja -DBOARD=atsamr21_xpro .. ninja flash
You should see “Hello World! arm” in your terminal.