Raspberry Pi Pico

Overview

The Raspberry Pi Pico and Pico W are small, low-cost, versatile boards from Raspberry Pi. They are equipped with an RP2040 SoC, an on-board LED, a USB connector, and an SWD interface. The Pico W additionally contains an Infineon CYW43439 2.4 GHz Wi-Fi/Bluetooth module. The USB bootloader allows the ability to flash without any adapter, in a drag-and-drop manner. It is also possible to flash and debug the boards with their SWD interface, using an external adapter.

Hardware

  • Dual core Arm Cortex-M0+ processor running up to 133MHz

  • 264KB on-chip SRAM

  • 2MB on-board QSPI flash with XIP capabilities

  • 26 GPIO pins

  • 3 Analog inputs

  • 2 UART peripherals

  • 2 SPI controllers

  • 2 I2C controllers

  • 16 PWM channels

  • USB 1.1 controller (host/device)

  • 8 Programmable I/O (PIO) for custom peripherals

  • On-board LED

  • 1 Watchdog timer peripheral

  • Infineon CYW43439 2.4 GHz Wi-Fi chip (Pico W only)

Raspberry Pi Pico
Raspberry Pi Pico W

Raspberry Pi Pico (above) and Pico W (below) (Images courtesy of Raspberry Pi)

Supported Features

The rpi_pico board configuration supports the following hardware features:

Peripheral

Kconfig option

Devicetree compatible

NVIC

N/A

arm,v6m-nvic

UART

CONFIG_SERIAL

raspberrypi,pico-uart

GPIO

CONFIG_GPIO

raspberrypi,pico-gpio

ADC

CONFIG_ADC

raspberrypi,pico-adc

I2C

CONFIG_I2C

snps,designware-i2c

SPI

CONFIG_SPI

raspberrypi,pico-spi

USB Device

CONFIG_USB_DEVICE_STACK

raspberrypi,pico-usbd

HWINFO

CONFIG_HWINFO

N/A

Watchdog Timer (WDT)

CONFIG_WATCHDOG

raspberrypi,pico-watchdog

PWM

CONFIG_PWM

raspberrypi,pico-pwm

Flash

CONFIG_FLASH

raspberrypi,pico-flash

Clock controller

CONFIG_CLOCK_CONTROL

raspberrypi,pico-clock-controller

UART (PIO)

CONFIG_SERIAL

raspberrypi,pico-uart-pio

SPI (PIO)

CONFIG_SPI

raspberrypi,pico-spi-pio

Pin Mapping

The peripherals of the RP2040 SoC can be routed to various pins on the board. The configuration of these routes can be modified through DTS. Please refer to the datasheet to see the possible routings for each peripheral.

External pin mapping on the Pico W is identical to the Pico, but note that internal RP2040 GPIO lines 23, 24, 25, and 29 are routed to the Infineon module on the W. Since GPIO 25 is routed to the on-board LED on the Pico, but to the Infineon module on the Pico W, the “blinky” sample program does not work on the W (use hello_world for a simple test program instead).

Default Zephyr Peripheral Mapping:

  • UART0_TX : P0

  • UART0_RX : P1

  • I2C0_SDA : P4

  • I2C0_SCL : P5

  • I2C1_SDA : P14

  • I2C1_SCL : P15

  • SPI0_RX : P16

  • SPI0_CSN : P17

  • SPI0_SCK : P18

  • SPI0_TX : P19

  • ADC_CH0 : P26

  • ADC_CH1 : P27

  • ADC_CH2 : P28

  • ADC_CH3 : P29

Programmable I/O (PIO)

The RP2040 SoC comes with two PIO periherals. These are two simple co-processors that are designed for I/O operations. The PIOs run a custom instruction set, generated from a custom assembly language. PIO programs are assembled using pioasm, a tool provided by Raspberry Pi.

Zephyr does not (currently) assemble PIO programs. Rather, they should be manually assembled and embedded in source code. An example of how this is done can be found at drivers/serial/uart_rpi_pico_pio.c.

Sample: SPI via PIO

The samples/sensor/bme280/README.rst sample includes a demonstration of using the PIO SPI driver to communicate with an environmental sensor. The PIO SPI driver supports using any combination of GPIO pins for an SPI bus, as well as allowing up to four independent SPI buses on a single board (using the two SPI devices as well as both PIO devices).

Programming and Debugging

Flashing

Using OpenOCD

To use PicoProbe, You must configure udev.

Create a file in /etc/udev.rules.d with any name, and write the line below.

ATTRS{idVendor}=="2e8a", ATTRS{idProduct}=="000c", MODE="660", GROUP="plugdev", TAG+="uaccess"

This example is valid for the case that the user joins to plugdev groups.

The Raspberry Pi Pico has an SWD interface that can be used to program and debug the on board RP2040. This interface can be utilized by OpenOCD. To use it with the RP2040, OpenOCD version 0.12.0 or later is needed.

If you are using a Debian based system (including RaspberryPi OS, Ubuntu. and more), using the pico_setup.sh [1] script is a convenient way to set up the forked version of OpenOCD.

Depending on the interface used (such as JLink), you might need to checkout to a branch that supports this interface, before proceeding. Build and install OpenOCD as described in the README.

Here is an example of building and flashing the Blinky application.

# From the root of the zephyr repository
west build -b rpi_pico samples/basic/blinky -- -DOPENOCD=/usr/local/bin/openocd -DOPENOCD_DEFAULT_PATH=/usr/local/share/openocd/scripts -DRPI_PICO_DEBUG_ADAPTER=picoprobe
west flash

Set the environment variables OPENOCD to /usr/local/bin/openocd and OPENOCD_DEFAULT_PATH to /usr/local/share/openocd/scripts. This should work with the OpenOCD that was installed with the default configuration. This configuration also works with an environment that is set up by the pico_setup.sh [1] script.

RPI_PICO_DEBUG_ADAPTER specifies what debug adapter is used for debugging.

If RPI_PICO_DEBUG_ADAPTER was not assigned, picoprobe is used by default. The other supported adapters are raspberrypi-swd, jlink and blackmagicprobe. How to connect picoprobe and raspberrypi-swd is described in Getting Started with Raspberry Pi Pico [2]. Any other SWD debug adapter maybe also work with this configuration.

The value of RPI_PICO_DEBUG_ADAPTER is cached, so it can be omitted from west flash and west debug if it was previously set while running west build.

RPI_PICO_DEBUG_ADAPTER is used in an argument to OpenOCD as “source [find interface/${RPI_PICO_DEBUG_ADAPTER}.cfg]”. Thus, RPI_PICO_DEBUG_ADAPTER needs to be assigned the file name of the debug adapter.

You can also flash the board with the following command that directly calls OpenOCD (assuming a SEGGER JLink adapter is used):

$ openocd -f interface/jlink.cfg -c 'transport select swd' -f target/rp2040.cfg -c "adapter speed 2000" -c 'targets rp2040.core0' -c 'program path/to/zephyr.elf verify reset exit'

Using UF2

If you don’t have an SWD adapter, you can flash the Raspberry Pi Pico with a UF2 file. By default, building an app for this board will generate a build/zephyr/zephyr.uf2 file. If the Pico is powered on with the BOOTSEL button pressed, it will appear on the host as a mass storage device. The UF2 file should be drag-and-dropped to the device, which will flash the Pico.

Debugging

The SWD interface can also be used to debug the board. To achieve this, you can either use SEGGER JLink or OpenOCD.

Using SEGGER JLink

Use a SEGGER JLink debug probe and follow the instruction in Building, Flashing and Debugging.

Using OpenOCD

Install OpenOCD as described for flashing the board.

Here is an example for debugging the Blinky application.

# From the root of the zephyr repository
west build -b rpi_pico samples/basic/blinky -- -DOPENOCD=/usr/local/bin/openocd -DOPENOCD_DEFAULT_PATH=/usr/local/share/openocd/scripts -DRPI_PICO_DEBUG_ADAPTER=raspberrypi-swd
west debug

As with flashing, you can specify the debug adapter by specifying RPI_PICO_DEBUG_ADAPTER at west build time. No needs to specify it at west debug time.

You can also debug with OpenOCD and gdb launching from command-line. Run the following command:

$ openocd -f interface/jlink.cfg -c 'transport select swd' -f target/rp2040.cfg -c "adapter speed 2000" -c 'targets rp2040.core0'

On another terminal, run:

$ gdb-multiarch

Inside gdb, run:

(gdb) tar ext :3333
(gdb) file path/to/zephyr.elf

You can then start debugging the board.