ItsyBitsy M4 Express

Overview

The Adafruit ItsyBitsy M4 express is a small (36 mm x 18 mm) ARM development board with an onboard RGB LED, USB port, 2 MiB of SPI flash, and range of I/O broken out onto 23 GPIO pins.

Hardware

  • ATSAMD51G19A ARM Cortex-M4 processor at 120 MHz

  • 512 KiB of flash memory and 192 KiB of RAM

  • 2 MiB of SPI flash

  • Internal trimmed 8 MHz oscillator

  • A user LED

  • An RGB DotStar LED

  • Native USB port

  • One reset button

Supported Features

The adafruit_itsybitsy_m4_express 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

USART

on-chip

Serial ports

SPI

on-chip

Serial Peripheral Interface ports

TRNG

on-chip

True Random Number Generator

HWINFO

on-chip

Unique 128 bit serial number

RTC

on-chip

Real-Time Counter

USB

on-chip

USB device

WDT

on-chip

Watchdog Timer

PWM

on-chip

PWM

Other hardware features are not currently supported by Zephyr.

The default configuration can be found in the Kconfig file boards/adafruit/itsybitsy_m4_express/adafruit_itsybitsy_m4_express_defconfig.

Zephyr can use the default Cortex-M SYSTICK timer or the SAM0 specific RTC. To use the RTC, set CONFIG_CORTEX_M_SYSTICK=n and set CONFIG_SYS_CLOCK_TICKS_PER_SEC to no more than 32 kHZ divided by 7, i.e. no more than 4500.

Connections and IOs

The Adafruit Learning System [1] has detailed information about the board including pinouts [2] and the schematic [3].

System Clock

The SAMD51 MCU is configured to use the 32 kHz internal oscillator with the on-chip PLL generating the 120 MHz system clock.

Serial Port

The SAMD51 MCU has 6 SERCOM based USARTs. On the ItsyBitsy, SERCOM3 is the Zephyr console and is available on pins 0 (RX) and 1 (TX).

SPI Port

The SAMD51 MCU has 6 SERCOM based SPIs. On the ItsyBitsy, SERCOM1 can be put into SPI mode and used to connect to devices over the SCK (SCLK), MO (MOSI), and MI (MISO) pins.

PWM

The SAMD51 has three PWM generators with up to six channels each. TCC_0 has a resolution of 24 bits and all other generators are 16 bit. TCC_1 pin 2 is mapped to PA18 (D7) and pin 3 is mapped to PA19 (D9).

USB Device Port

The SAMD51 MCU has a USB device port that can be used to communicate with a host PC. See the USB device support sample applications for more, such as the USB CDC-ACM sample which sets up a virtual serial port that echos characters back to the host PC.

Programming and Debugging

The ItsyBitsy ships with a the BOSSA compatible UF2 bootloader. The bootloader can be entered by quickly tapping the reset button twice.

Additionally, if CONFIG_USB_CDC_ACM is enabled then the bootloader will be entered automatically when you run west flash.

Flashing

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

    west build -b adafruit_itsybitsy_m4_express samples/hello_world

  2. Connect the ItsyBitsy to your host computer using USB

  3. 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.

  4. 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

  5. Tap the reset button twice quickly to enter bootloader mode

  6. Flash the image:

    west build -b adafruit_itsybitsy_m4_express samples/hello_world
west flash

    You should see “Hello World! adafruit_itsybitsy_m4_express” in your terminal.

Debugging

In addition to the built-in bootloader, the ItsyBitsy can be flashed and debugged using a SWD probe such as the Segger J-Link.

  1. Connect the board to the probe by connecting the SWCLK, SWDIO, RESET, GND, and 3V3 pins on the ItsyBitsy to the SWCLK, SWDIO, RESET, GND, and VTref pins on the J-Link [4].

  2. Flash the image:

    west build -b adafruit_itsybitsy_m4_express samples/hello_world
west flash -r openocd

  3. Start debugging:

    west build -b adafruit_itsybitsy_m4_express samples/hello_world
west debug

References