picoRTOS

Very small, lightning fast, yet portable RTOS with SMP suppport

Presentation

picoRTOS is a teeny tiny RTOS with as little overhead as humanely possible.

Supported architectures

Single core

• ARM Cortex-M0+
• ARM Cortex-M3
• ARM Cortex-M4F
• ATmega2560 / AVR6
• ATmega328P / AVR5
• TI C2000 / C28x
• PowerPC e200z4
• PowerPC e200z7

Multi-core SMP

• PowerPC e200z4 SMP
• PowerPC e200z7 SMP
• RP2040 SMP (Raspberry Pico)

Simulation

• POSIX threads / Linux
• WIN32 threads / Windows

Working principle

On every new schedule (tick) task 0 is executed first. Any call to a sleeping function (picoRTOS_schedule, picoRTOS_sleep or picoRTOS_sleep_until) will allow the scheduler to move to the next task until it reaches idle or a new tick occurs and the cycle starts over.

To increase speed and predictability, every task is identified by its exclusive level of priority, no round robin support is offered.

No memory management is offered, everything is static, which makes the static analyzer's job much easier for critical applications.

Advanced features

IPCs are available to architectures that support the correct associated atomic operations. A small infringement has been made to the hard real time philosophy of the project by supporting the CONFIG_ARCH_EMULATE_ATOMIC on platforms that don't support native atomic operations. This is not recommended, though.

The following IPCs are provided:

• spinlocks (require arch_test_and_set)
• futexes (require arch_test_and_set)
• re-entrant mutexes (require arch_compare_and_swap)
• conditions (require mutexes)

How to use

Copy the picoRTOS directory in your project and add picoRTOS.c to your build.

Create a picoRTOSConfig.h file at the root of your project. Sample configs are available for every supported cpu in arch/x/y/samples

Then, add the relevant arch files to your build.

Example for ARM Cortex-M0+:

SRC += picoRTOS/picoRTOS.c
SRC += picoRTOS/arch/arm/cm0+/picoRTOS_port.c
SRC += picoRTOS/arch/arm/cm0+/picoRTOS_portasm.S
CFLAGS += -IpicoRTOS -IpicoRTOS/arch/include -IpicoRTOS/arch/arm/cm0+

Code-wise, using picoRTOS is quite straightforward :

#include "picoRTOS.h"

void main(void)
{
    picoRTOS_init();

    struct picoRTOS_task task0;
    struct picoRTOS_task task1;
    static picoRTOS_stack_t stack0[CONFIG_DEFAULT_STACK_COUNT];
    static picoRTOS_stack_t stack1[CONFIG_DEFAULT_STACK_COUNT];
    ...

    picoRTOS_task_init(&task0, task0_main, &task0_context, stack0, CONFIG_DEFAULT_TASK_COUNT);
    picoRTOS_task_init(&task1, task1_main, &task1_context, stack1, CONFIG_DEFAULT_TASK_COUNT);
    ...

    picoRTOS_add_task(&task0, TASK0_PRIO);
    picoRTOS_add_task(&task1, TASK1_PRIO);
    ...

    picoRTOS_start();
}

Hint: tasks are converted to internal structures in picoRTOS_add_task and can be local but stacks need to be persistant (prefer static to globals to reduce scope).

Demo

A bunch of demo code is available under the demo directory so you can see for yourself if this software suits your needs.