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Gettings started

This is a written expleanation of the video tutorial on how to get started with FreeRTOS on the Raspberry Pi Pico

This uses picosdk (SDK 1.5.1) and FreeRTOS (V11.0.1)

1. Clone the Repo

git clone https://github.com/lowlevellearning/rp2040-freertos
cd rp2040-freertos

2. Adding necessary libraries

We need to add the PICO-SDK and FreeRTOS to the project.

2.1 Add PICO-SDK

This is dependend on your setup. If you have the PICO-SDK installed, you may need to add the path to the PICO_SDK_PATH to point to the location of the SDK.

export PICO_SDK_PATH=/path/to/pico-sdk

If you don't have the SDK installed, you can clone it from the official repo.

git clone https://github.com/raspberrypi/pico-sdk
export PICO_SDK_PATH=$PWD/pico-sdk

You may also need to install the toolchain. You can find the instructions for that in original video or in the getting-started PDF

2.2 Adding FreeRTOS

git clone https://github.com/FreeRTOS/FreeRTOS-Kernel
cd FreeRTOS-Kernel
git checkout V11.0.1
cd ..

3. Build the project

cd build
rm -rf * # This nukes the entire build folder, to have a clean slate
cmake ..
# -j4 means that it will use 4 threads to compile, this can be modified to your liking
make -j4

4. Flash to the Pico

Unplug the Pico, press and hold the BOOTSEL button, plug the Pico back in, release the BOOTSEL button. The Pico should now appear as a USB drive on your computer. By copying a file to this drive you can flash the program to the Pico.

This can be done via drag and drop or:

cp blink.uf2 </path/to/pico>

(were </path/to/pico> is the path to the USB drive)

FREE-RTOS Issue

TLDR

Use FreeRTOS V11.0.1 (commit: 0240cd5) instead of V11.1.0 (commit: dbf7055) by running git checkout 0240cd5 in FreeRTOS-Kernel folder

Currently (Jun 22, 2024) freertos is not working correctly with the rpi pico since release V11.1.0 (commit: dbf7055).

When trying to build the project will get this error

error: #error configENABLE_MPU must be defined in FreeRTOSConfig.h. Set configENABLE_MPU to 1 to enable the MPU or 0 to disable the MPU

when doing so by adding #define configENABLE_MPU 0 or #define configENABLE_MPU 1 to the FreeRTOSConfig.h file, the following error will appear in multiple freertos related files:

tasks.c:(privileged_functions+0xecc): undefined reference to `vClearInterruptMask'

This issue can be avoided by using the older version of FreeRTOS: V11.0.1 (commit: 0240cd5)

You can just checkout the correct version by running:

git checkout 0240cd5

This will checkout the correct version of FreeRTOS. You can now build the project as usual.