Raspberry Pi Pico Bare-Metal RTOS

A low-level Real-Time Operating System kernel written in Zig, targeting the Raspberry Pi RP2350 (Pico 2) microcontroller. This project focuses on high-performance, memory-safe embedded programming without the overhead of the standard C SDK.

Project Status: Platform Transition

Important: Development for the RP2040 has been officially discontinued and abandoned. The codebase has been entirely refactored to focus exclusively on the RP2350 architecture.

The transition introduces support for:

• ARM Cortex-M33 instruction set.
• Picobin Image Definition Blocks (mandatory for RP2350 booting).
• TrustZone security state management (Secure/Non-secure modes).
• Updated Peripheral and IO_BANK0 register mapping.

Prerequisites

To build and flash this project, the following tools are strictly required:

• Zig Compiler: Latest nightly/master branch (tested with 0.14.0-dev).
• GNU Make: To automate the build and UF2 conversion process.
• picotool (v2.0 or higher): Used for uploading the final firmware to the device.
• LLVM Tools: llvm-objdump and llvm-nm for binary analysis.

Hardware Support

• Microcontroller: Raspberry Pi RP2350.
• Target Board: Raspberry Pi Pico 2.
• Architecture: ARMv8-M (Cortex-M33).

Building and Flashing

The project utilizes a Makefile to handle the Zig compilation and the subsequent conversion of the ELF binary into a valid UF2 image with the required RP2350 headers.

1. Build the Firmware

Running this command will compile the Zig source and generate the UF2 file in the output directory.

make rp2350

2. Flash to Device

Once the UF2 file is generated, put the Pico 2 into BOOTSEL mode and use picotool to upload the firmware:

picotool load out/image_rp2350.uf2

Technical Architecture

Image Definition Block (IDB)

The RP2350 requires a Tag-based Image Definition Block at the very beginning of the Flash memory. This project implements a custom ImageDefBlock at offset 0x00 of the Flash (0x10000000) to signal the BootROM to initialize the ARM core in Secure mode and define the Vector Table location.