The RP2040 PIO emulator is a collection of software tools that consists of

  • a software emulation of the core PIO parts of the Raspberry Pi Foundation’s RP2040 chip, and
  • some client applications for controlling the emulator and observing and visualising its progress and internal state.

The software is intended as highly valuable collection of tools for assistance in developing and debugging PIO programs for the RP2040.

Server Console, Monitor Control Program, Timing Diagram and GPIO Observer

Server Console, Monitor Control Program, Timing Diagram and GPIO Observer at a Glance

A typical development / debugging session with server console running in a standard terminal, client-side monitor for control and inspection, timing diagram for watching signals and GPIO Observer for watching current status of GPIO pins.


In late January of 2021, the Raspberry Pi Foundation [RPF21a] announced their new Raspberry Pi Pico [RPF21b], that the foundation designed by itself.

Besides two dual-core Arm Cortex-M0+ processor core, the RP2040 chip also features two programmable I/O blocks (PIO) that are highly interesting components, each including 4 so-called state machines (SM), internal instruction memory, 8 FIFOs, and some more logic components. The state machines are, essentially, extremely simple but fast microprocessors that run in parallel and independent from the main CPU cores, and are specialized on bit processing for the microcontroller’s GPIO pins. The concept of side-sets provides for even more parallelism of bit manipulations, but also produces side-effects that are challenging to handle. Typical applications of PIO programs are implementations of I/O protocols such as, for example, I²C, SPI, UART, Manchester Serial Protocol, PWM, or even WS2812.


Developing PIO programs is extremely challenging due to the PIO’s highly specialized set of instructions oriented at bit-manipulation and due to their parallel side-effects. Even worse, there is no way for debugging a PIO program on a real RP2040 chip. Consequently, the only way to debug a PIO program is to emulate all state machines’ behaviour and their interaction with external components.


This is exactly, what the RP2040 PIO emulator does: It aims to mimick the behaviour of all of the two PIOs’ state machines (8 units altogether plus 8 FIFOs and some more glue logic) as precise as necessary to reproduce their logical functionality, such that PIO programs can be debugged in the emulator, thus making it feasible to develop programs for the PIO.