Less than two weeks ago, after 584 days since I started working on distortos system, I finally published first version - 0.1.0. List of functionalities included in this release can be found in the change log and packages with source code can be found on http://distortos.org/ in Downloads section. In the same place you can also download packages with project template and example applications that were published on the same day. This second package currently has just the "classic" LED blinker which uses static or dynamic threads. I've even recorded a short video featuring this application (;

As a small incentive - a little bit of "magic" code, which asynchronously calculates result of sine function for four different numbers in four separate threads. It is a complete and working code of application - you don't need to add anything else!

#include "distortos/board/leds.hpp"
#include "distortos/chip/ChipOutputPin.hpp"
#include "distortos/StaticThread.hpp"

void sinWrapper(const double operand, double& result)
{
  result = sin(operand);
}

int main()
{
  const double operands[4] {0.9867816015, 0.4641984149, 0.4665572273, 0.8926178650};
  double results[4] {};
  auto sinThread0 = distortos::makeAndStartStaticThread<512>(1, sinWrapper, operands[0], std::ref(results[0]));
  auto sinThread1 = distortos::makeAndStartStaticThread<512>(1, sinWrapper, operands[1], std::ref(results[1]));
  auto sinThread2 = distortos::makeAndStartStaticThread<512>(1, sinWrapper, operands[2], std::ref(results[2]));
  auto sinThread3 = distortos::makeAndStartStaticThread<512>(1, sinWrapper, operands[3], std::ref(results[3]));

  // do something while the threads are calculating results...
  distortos::board::leds[0].set(true);

  // make sure the threads are done
  sinThread0.join();
  sinThread1.join();
  sinThread2.join();
  sinThread3.join();

  // results are ready!
  distortos::board::leds[0].set(false);
}

A few weeks ago distortos project - advanced real-time operating system - got its own website, which is available at http://distortos.org/. For now it contains only a few short news articles, a few useful links and source code documentation generated with doxygen tool, but the amount of useful content will constantly increase.

On the other hand, complete support for all 115 chips from the STM32F4 family was added to the Kconfig configuration system and to the source code of the project. Two more example configurations for popular boards with STM32F4 chips were also added, so there are now three tested, ready to run configurations:

• classic STM32F4DISCOVERY board with STM32F407VG chip (168MHz max),
• 32F429IDISCOVERY board (also known as STM32F429-DISCO) with STM32F429ZI chip (180MHz max),
• small and very cheap NUCLEO-F401RE board with STM32F401RE chip (84MHz max).

All these configurations run the test application at the max possible system clock frequency. Whole configuration of the clock system frequency and some details from the power system is done with the Kconfig configuration tool, presented on the screenshots below.

Kconfig, STM32F4

Kconfig, STM32F4

Kconfig, STM32F4

The correctness of the selected configuration is verified partly in the Kconfig tool and partly in the source code, using only compile-time methods (static_assert(…) or preprocessor).

One year and one day passed since I started writing my own RTOS. distortos project is still evolving and - as of today - has 1542 commits. Since previous news article only two new features were implemented, but both of them are rarely seen in other RTOSes. One of them is OnceFlag class with callOnce() function - which are equivalents of std::once_flag class and std::call_once() function from C++11 standard or pthread_once_t structure and pthread_once() function from <pthread.h>.

Second new feature is an implementation of POSIX signals. Signals can be handled both by synchronous waiting - with ThisThread::Signals::wait(), ThisThread::Signals::tryWait(), ThisThread::Signals::tryWaitFor() andThisThread::Signals::tryWaitUntil() functions - and by asynchronous signal handlers - using ThisThread::Signals::setSignalAction() function. As in the established standards, delivery of signal causes interruption of some blocking functions (like Semaphore::wait() or MessageQueue::pop()), which return EINTR error code in that case. Looking at this feature from the other side - from the "source" of the signal - it is possible to "generate" the signal (ThreadBase::generateSignal()) or "queue" the signal with a value (ThreadBase::queueSignal()). Obviously, the signals can also be masked and ignored.

All of that is - still - possible without a single byte of dynamically allocated memory! In case of static threads (StaticThread instances) it is necessary to state whether the thread can receive the signals at all, how many signals can be queued simultaneously and how many different SignalAction objects can be used at the same time.

Stay tuned!

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distortos project - mentioned in previous news article - is still evolving. Today it is exactly 7 months since the first commit in the repository, and the total number of these commits reached a nice value of 1023. Many readers - at least those who are a bit into RTOSes for microcontrollers - may wonder "who needs another RTOS project?". Answer to this question is very complex and I could write a separate article about that, so for now a link to README file - in which I tried to explain the main reasons for this project's existence - must suffice. I think that at least the huge emphasis placed on C++ and C++11 support makes this project worthwhile, although this feature should not diminish other advantages (some of which are of course "future" (; ), important for people who don't intend to use C++ (this feature is one of the "future" ones for sure, as for now only C++11 API is available).

There are still many features missing, but these 7 months were well spent - quite a lot was done, and these things work remarkably well (;

The most important features are obviously threads (Thread, StaticThread and ThreadBase classes), which can accept any number of arguments of any type - thanks to new features of C++11 standard - not only the void* known from other RTOSes. Moreover - regular functions, member functions, functors or lambdas can be used as thread's function.

All of these features are also present in software timers (SoftwareTimer class).

Scheduler supports full preemption based on thread's priority (there are 256 priority levels), and when several threads with the same priority are present, they are scheduled according to FIFO or round-robin algorithm (selected for each thread individually).

Semaphore (Semaphore class) is probably the most basic synchronization object. It is possible to configure maximal value the semaphore can "have", so this object can also be used as binary semaphore. Semaphores can be "posted" from interrupts.

Mutex (Mutex class) is one of more advanced synchronization mechanisms. Just as in POSIX standard, it can be configured to use any of the three "modes" - normal, error-checking or recursive - and any of the three "protocols" - normal, priority inheritance or priority protocol (also known as priority ceiling). Unlike many other RTOSes, priority inheritance protocol works with no limitations: through any number of inheritance "levels" and with any number of mutexes locked by threads in any order (diagram and description of test case of this particular feature).

Classic condition variable (ConditionVariable class) is a mechanism which extends functionality of mutexes.

Queues can be used for standard communication between threads and interrupts (in any combination). There are four variants of queues:

• without priorities, without support for objects (RawFifoQueue and StaticRawFifoQueue classes),
• without priorities, with support for objects (FifoQueue and StaticFifoQueue classes),
• with priorities, without support for objects (RawMessageQueue and StaticRawMessageQueue classes),
• with priorities, with support for objects (MessageQueue and StaticMessageQueue classes).

Messages added to queues which don't support priorities (...FifoQueue) are ordered in FIFO order, while queues which do support priorities (...MessageQueue) allow adding messages with one of 256 priority levels. Queues without support for objects (...Raw...) copy the messages with memcpy() function, while queues with support for objects use all operations required in such scenario (construction, destruction, assignment operator, swap, emplace, ...).

All blocking operations are also available in non-blocking variants and in blocking versions with timeout (absolute or relative), which - thanks to C++11 std::chrono - can be easily expressed in any unit (like seconds, minutes, hours, ... - link), not only in system "ticks".

All errors are signaled with error codes - functions use neither errno variable, nor C++ exceptions.

The only supported architecture - for now - is ARMv7-M, so ARM Cortex-M3 (ARM Cortex-M4 can be used without enabling FPU) (added 20.03.2015) and ARM Cortex-M4(F), and the only "officially" supported chip is STM32F407VG (known from STM32F4Discovery board), although using any different chip with proper core would be trivial.

I saved the best part (I hope) for the end - use of all functionalities mentioned above is possible without dynamic memory allocation. All previously described objects can be constructed as global variables or on stack.

I'm sure I forgot to mention some more interesting features...

Feel encouraged to test the code, ask questions, post comments, send suggestions and cooperate (; Stay tuned!

I was thinking about doing something like that for a long time... However usually intent is far away from something concrete, especially when you don't have that much free time in your hands. Finally I pulled myself together, so here is a little "teaser" of what I'm currently working on (among other things).

bool ThreadFunctionTypesTestCase::run_() const
{
    using scheduler::makeStaticThread;

    // thread with regular function
    {
        uint32_t sharedVariable {};
        constexpr uint32_t magicValue {0x394e3bae};

        auto regularFunctionThread = makeStaticThread<testThreadStackSize>(UINT8_MAX,
                regularFunction, std::ref(sharedVariable), magicValue);
        regularFunctionThread.start();
        regularFunctionThread.join();

        if (sharedVariable != magicValue)
            return false;
    }

    // thread with state-less functor
    {
        uint32_t sharedVariable {};
        constexpr uint32_t magicValue {0x2c2b7c30};

        auto functorThread = makeStaticThread<testThreadStackSize>(UINT8_MAX, Functor{},
                std::ref(sharedVariable), magicValue);
        functorThread.start();
        functorThread.join();

        if (sharedVariable != magicValue)
            return false;
    }

    // thread with member function of object with state
    {
        constexpr uint32_t magicValue {0x33698f0a};
        Object object {magicValue};

        auto objectThread = makeStaticThread<testThreadStackSize>(UINT8_MAX,
                &Object::function, std::ref(object));
        objectThread.start();
        objectThread.join();

        if (object.getVariable() != magicValue)
            return false;
    }

    // thread with capturing lambda
    {
        uint32_t sharedVariable {};
        constexpr uint32_t magicValue {0x24331acb};

        auto capturingLambdaThread = makeStaticThread<testThreadStackSize>(UINT8_MAX,
                [&sharedVariable, magicValue]()
                {
                    sharedVariable = magicValue;
                });
        capturingLambdaThread.start();
        capturingLambdaThread.join();

        if (sharedVariable != magicValue)
            return false;
    }

    return true;
}

Intriguing? Curious? Interesting? (;

It's a fragment of functional tests of an open-source project, which currently is in early alpha stage (first line of code was written just last month), but basic things - like the ones shown in the piece of code above - are working (on STM32F4) pretty well (; There is not much to say now, the only trace of this project is the github repository and this news... Just like in any open-source project the most important things are the users and the community, so any thoughts, ideas, remarks, opinions etc. can be posted here - in comments - or on github. If anyone's up for some coding, I'm open to cooperation. Work is ongoing, so "stay tuned" (;

Complete source file from which the fragment above was taken can be seen under this link.