The SMP (multicore) port of FreeRTOS is included with the core. This allows complex task operations and real preemptive multithreading in your sketches. While the setup1 and loop1 way of multitasking is simplest for most folks, FreeRTOS is much more powerful.

Enabling FreeRTOS

To enable FreeRTOS, simply add

#include <FreeRTOS.h>

to your sketch and it will be included and enabled automatically.

Configuration and Predefined Tasks

FreeRTOS is configured with 8 priority levels (0 through 7) and a process for setup()/loop(), setup1()/loop1(), and the USB port will be created. The task quantum is 1 millisecond (i.e. 1,000 switches per second).

setup() and loop() are assigned to only run on core 0, while setup1() and loop1() only run in core 1 in this mode, the same as the default multithreading mode.

You can launch and manage additional processes using the standard FreeRTOS routines.

delay() and yield() free the CPU for other tasks, while delayMicroseconds() does not.


While the core now supports FreeRTOS, most (probably all) Arduino libraries were not written to support preemptive multithreading. This means that all calls to a particular library should be made from a single task.

In particular, the LittleFS and SDFS libraries can not be called from different threads. Do all File operations from a single thread or else undefined behavior (aka strange crashes or data corruption) can occur.

More Information

For full FreeRTOS documentation look at and FreeRTOS SMP support.