Raspberry Pi Pico

Support for the RP2040 based Raspberry Pi Pico board. More...

Detailed Description

Support for the RP2040 based Raspberry Pi Pico board.

Overview

The Raspberry Pi Pico is sold by the Raspberry Pi foundation for about 4 USD. It features the RP2040 MCU, a custom dual core ARM Cortex-M0+ MCU with relatively high CPU clock, plenty of RAM and some unique peripheral (the Programmable IO).

Hardware

MCU

The Programmable IO (PIO) peripheral and the SSI/QSPI peripheral that supports execution from flash (XIP) are the most distinguishing features of the MCU. The latter is especially important, since the RP2040 contains no internal flash.

MCU	RP2040
Family	(2x) ARM Cortex-M0+
Vendor	Raspberry Pi
RAM	264 KiB
Flash	2 MiB (up to 16 MiB)
Frequency	up to 133 MHz
FPU	no
PIOs	8
Timers	1 x 64-bit
ADCs	1x 12-bit (4 channels + temperature sensor)
UARTs	2
SPIs	2
I2Cs	2
RTCs	1
USBs	1 (USB 2.0)
Watchdog	1
SSI/QSPI	1 (connected to flash, with XIP support)
Vcc	1.62V - 3.63V
Datasheet	Datasheet

User Interface

1 button (also used for boot selection) and 1 LED:

Device	PIN
LED0	25
SW0	QSPI_SS_N (*)

(*) Since the switch is connected to the chip-select pin of the QSPI interface the flash chip RIOT is running from via XIP, the switch is difficult to read out from software. This is currently not supported.

Pinout

Flashing the Board

Flashing the Board Using the Bootloader

Connect the device to your Micro-USB cable while the button (labeled BOOTSEL on the silkscreen of the PCB) is pressed to enter the bootloader. The pico will present itself as a storage medium to the system, to which a UF2 file can be copied perform the flashing of the device. This can be automated by running:

make BOARD=rpi-pico flash

This is default flashing option using elf2uf2 PROGRAMMER. If the storage is not automatically mounted to /media/<USER_NAME>/RPI-RP2, you can overwrite the path by exporting the shell environment variable ELF2UF2_MOUNT_PATH.

Flashing the Board Using OpenOCD

Currently (June 2021), only two methods for debugging via OpenOCD are supported:

1. Using a bit-banging low-level adapter, e.g. via the GPIOs of a Raspberry Pi 4B
2. Using a virtual CMSIS-DAP adapter provided by the second CPU core via https://github.com/majbthrd/pico-debug

Option 2 requires no additional hardware however, you need to first "flash" the gimme-cache variant of pico-debug into RAM using the UF2 bootloader. For this, plug in the USB cable while holding down the BOOTSEL button of the Pico and copy the pico-debug-gimmecache.uf2 from the latest pico-debug release into the virtual FAT formatted drive the bootloader provides. Once this drive is unmounted again, this will result in the Raspberry Pi Pico showing up as CMSIS-DAP debugger. Afterwards run:

make BOARD=rpi-pico PROGRAMMER=openocd flash

Warning

The rpi-pico virtual debugger is not persistent and needs to be "flashed" into RAM again after each cold boot.

Note

As of July 2021, the latest stable release of OpenOCD does not yet support the RP2040 MCU. Instead, compile the current master branch from the upstream OpenOCD source. The OpenOCD fork of the Raspberry Pi foundation is incompatible with OpenOCD configuration provided, so please stick with upstream OpenOCD.

Flashing the Board Using J-Link

Connect the Board to an Segger J-Link debugger, e.g. the EDU mini debugger is relatively affordable, but limited to educational purposes. Afterwards run:

make BOARD=rpi-pico PROGRAMMER=jlink flash

Accessing RIOT shell

This board's default access to RIOT shell is via UART (UART0 TX - pin 1, UART0 RX - pin 2).

The default baud rate is 115 200.

The simplest way to connect to the shell is the execution of the command:

make BOARD=rpi-pico term

Warning

Raspberry Pi Pico board is not 5V tolerant. Use voltage divider or logic level shifter when connecting to 5V UART.

On-Chip Debugging

There are currently (June 2021) few hardware options for debugging the Raspberry Pi Pico:

1. Via J-Link using one of Seggers debuggers
2. Via OpenOCD using a low-level bit-banging debugger (e.g. a Raspberry Pi 4B with the GPIOs connected to the Raspberry Pi Pico via jump wires)
3. Via a recently updated Black Magic Probe

In addition, a software-only option is possible using pico-debug. The default linker script reserved 16 KiB of RAM for this debugger, hence just "flash" the "gimme-cache" flavor into RAM using the UF2 bootloader. Once this is done, debugging is as simple as running:

make BOARD=rpi-pico debug

Beware:*** The rpi-pico virtual debugger is not persistent and needs to be "flashed" into RAM again after each cold boot. The initialization code of RIOT now seems to play well with the debugger, so it remains persistent on soft reboots. If you face issues with losing connection to the debugger on reboot, try monitor reset init in GDB to soft-reboot instead.

Known Issues / Problems

Early state Implementation

Currently no support for the following peripherals is implemented:

• Timers
• ADC
• SPI
• I2C
• USB
• PIO
• RTC
• Watchdog
• SMP support (multi CPU support is not implemented in RIOT)

Files
file	board.h
	Board specific definitions for the Raspberry Pi Pico.
file	gpio_params.h
	Board specific configuration of direct mapped GPIOs.
file	periph_conf.h
	Configuration of CPU peripherals for the Raspberry Pi Pico.