RTOS Sample Project for Raspberry Pi Pico 2 (Multicore)

This project demonstrates a hybrid implementation of FreeRTOS and Bare-metal execution on the Raspberry Pi Pico 2 (RP2350), utilizing both processor cores.

Project Description

The project showcases how to run a Real-Time Operating System (FreeRTOS) on one core while maintaining a high-precision hardware-timer-driven process on the second core.

Core 0: FreeRTOS

Core 0 runs the FreeRTOS scheduler and manages multiple concurrent tasks:

1. LED Blink Task: Uses a custom C++ class Pico2LED to toggle the built-in LED every 200ms.
2. USB Print Task: Prints the system status to the USB serial console every 1 second, including counters from both cores.

Core 1: Bare-metal (Hardware Timers)

Core 1 operates in a bare-metal mode to ensure maximum predictability and precision:

• It creates a dedicated Hardware Alarm Pool.
• It runs a Repeating Timer that increments a global counter every 1000ms via a hardware interrupt.
• The core remains in a low-power state (__wfi) until the next interrupt occurs.

Algorithm Description

The project implements a multi-core synchronization and execution flow:

1. Initialization (Core 0):
   • Initialize standard I/O.
   • Launch Core 1 using multicore_launch_core1().
2. Bare-metal Execution (Core 1):
   • Initialize a hardware alarm pool specifically for Core 1.
   • Schedule a repeating timer interrupt.
   • Enter a loop of "Wait For Interrupt" (__wfi).
3. RTOS Execution (Core 0):
   • Create FreeRTOS tasks for LED control and USB logging.
   • Start the scheduler via vTaskStartScheduler().
4. Inter-core Communication:
   • Core 0 reads the core1_counter variable (marked as volatile to prevent compiler optimization) to display the hardware timer's progress.

Installation and Setup

1. Prerequisites

Ensure you have the Raspberry Pi Pico SDK installed and configured.

2. FreeRTOS Sources Setup

mkdir freertos_sources
cd freertos_sources
git clone https://github.com/raspberrypi/FreeRTOS-Kernel
git clone https://github.com/jondurrant/RPIPico2-Exp
cp -r RPIPico2-Exp/examples/FreeRTOSBlink/port ../port/FreeRTOS-Kernel
cp RPIPico2-Exp/examples/FreeRTOSBlink/FreeRTOS_Kernel_import.cmake ../FreeRTOS_Kernel_import.cmake

3. Build Process

1. mkdir build && cd build
2. cmake ..
3. make
4. Flash the .uf2 file to the Pico 2.

Project Structure

• rtos_sample.cpp: Main application code (Multi-core logic).
• CMakeLists.txt: Build configuration.
• port/: FreeRTOS configuration and port files.
• freertos_sources/: FreeRTOS kernel and support libraries.