Raspberry Pi unveils $4 microcontroller board with custom chip
The Raspberry Pi Pico, says the organization, can be used as a standalone board for deep-embedded development, a companion to the Raspberry Pi computer, or a platform to learn about how to use a microcontroller. The board is based around the RP2040 microcontroller chip designed by Raspberry Pi, which features a dual-core Arm Cortex-M0+ processor with 264KB internal RAM and support for up to 16 MB of off-chip Flash.
The Pico, says the organization, addresses the need for a companion for the Raspberry Pi that uses less power and can handle analog input and low-latency I/O and, sometimes, provide a very low-power standby mode. Previously many hobbyist and industrial applications have paired a Raspberry Pi with a third-party microcontroller to achieve this.
“Until now,” says James Adams, Director of Hardware at Raspberry Pi, “we’ve not been able to figure out a way to make a compelling microcontroller-class product of our own. To make the product we really wanted to make, first we had to learn to make our own chips.”
Building on the lessons the organization has learned from using other microcontrollers in its products, it had three principal design goals for the RP2040: high performance, particularly for integer workloads; flexible I/O, to allow it to talk to almost any external device; and, low cost, to eliminate barriers to entry. The resulting chip is a 7 x 7 mm QFN-56 package containing just two square millimeters of 40 nm silicon.
Key features of the RP2040 include:
- Dual-core Arm Cortex-M0+ @ 133 MHz
- 264 KB of on-chip RAM
- Support for up to 16 MB of off-chip Flash memory via dedicated QSPI bus
- DMA controller
- Interpolator and integer divider peripherals
- 30 GPIO pins, four of which can be used as analog inputs
- 2 × UARTs, 2 × SPI controllers, and 2 × I2C controllers
- 16 × PWM channels
- 1 × USB 1.1 controller and PHY, with host and device support
- 8 × Raspberry Pi Programmable I/O (PIO) state machines
- USB mass-storage boot mode with UF2 support, for drag-and-drop programming
With six independent banks of RAM, and a fully connected switch at the heart of its bus fabric, says the organization, users can easily arrange for the cores and DMA engines to run in parallel without contention. For power users, a complete C SDK, a GCC-based toolchain, and Visual Studio Code integration are available.
The organization has also commissioned optimized floating-point functions for ARM Cortex-M cores from Mark Owen, author of the popular Qfplib libraries; these are substantially faster than their GCC library equivalents, and are licensed for use on any RP2040-based product.
“With two fast cores and and a large amount of on-chip RAM,” says Adams, “RP2040 is a great platform for machine learning applications.”
Pete Warden’s port of Google’s TensorFlow Lite framework is currently available, and more machine learning content is planned over the coming months. For beginners, and other users who prefer high-level languages, the organization has worked with Damien George, creator of MicroPython, to build a port for the RP2040, which exposes all of the chip’s hardware features, including its PIO subsystem.
The Raspberry Pi Pico is designed as a low-cost breakout board for the RP2040, pairing the RP2040 with 2 MB of Flash memory, and a power supply chip supporting input voltages from 1.8 to 5.5 V. This allows users to power the Pico from a wide variety of sources, including two or three AA cells in series, or a single lithium-ion cell.
Pico provides a single push button, which can be used to enter USB mass-storage mode at boot time and also as a general input, and a single LED. It exposes 26 of the 30 GPIO pins on the RP2040, including three of the four analog inputs, to 0.1”-pitch pads; users can solder headers to these pads or take advantage of their castellated edges to solder Pico directly to a carrier board.
Complete documentation for the Raspberry Pi Pico, and the RP2040, its SDK and toolchain, are available, as is Get Started with MicroPython on Raspberry Pi Pico, which is offered as ideal for beginners who are new to making with microcontrollers. An educational project – Getting started with Raspberry Pi Pico – is also available.
The organization is also working with Adafruit, Arduino, Pimoroni and Sparkfun so that they can build their own boards using the RP2040 chip. There will be an entire ecosystem of RP2040-powered devices.
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