FreeRTOS on the Raspberry Pi Pico (RP2040) Part 3: Scheduling and Task Priorities

FreeRTOS is an open source Real Time OS available for a wide range of microcontrollers and this video is part 3 in a series on using FreeRTOS on RP2040 based boards such as the Raspberry Pi Pico. In this video we show you how the FreeRTOS scheduling algorithm works. We also cover task priorities and task states. By the end of this tutorial you will have a project which explains how task priorities affect task scheduling.

In this tutorial we create a simple program where a Raspberry Pi Pico uses two FreeRTOS tasks to print to a command line over the USB interface which task is running.

Timestamps
00:00 Introduction
01:08 Task Scheduler
03:16 Tick Interrupt
03:32 Context Switching
04:25 Task States
06:13 Task Priorities
07:26 Example
09:58 Conclusions

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[jackyli]

this video is the best tutorial on how to lean FreeRTOS that i have never seen before...! good job!

[andrewkuhl]

This video crushes I love the way you do things

[omerkurt]

This video series is so clear and educative. I hope you will continue.

[crckdns]

Finally the scheduling coverage!
Thanks!

[thisnthat]

Interesting that a higher priority task can essentially hog the entire CPU.
From memory, the way AmigaOS handled scheduling was it would create a list of all tasks with their priorities, then iterate through the list, subtracting from the priority as it went. Only tasks with priority > 0 would be executed. Once all tasks had reached 0, the list would be repopulated with the original priority value and the process would repeat. This way, even the lowliest task would get some CPU allocation, but a task with priority 10 would get 10x the time slices of a task with priority 1 for example.

[lfarge]

Great content as usual. What about installing FreeRTOS on both cores of the Pico...that would be a great topic! :-)

[GIJOEG]

This delay will only work if compiled without optimisation....

[helmutzollner]

That means that high priority task need to cooperate by entering the delay stage in order to give lower priority tasks a chance to execute?
That appears to be not very useful. There is no way to divide the available slots up to all the tasks and give them more or less time slices?
Or is that a problem with the idea of an RTOS?

[tuncayusta]

if you want time slicing among equal priorities in the example with for loops, you need to turn on "configUSE_TIME_SLICING" in "FreeRTOSConfig.h".