FreeRTOS
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FreeRTOS is an open source real-time operating system that allows for multitasking on microcontrollers using preemptive scheduling. It uses queues to allow tasks to communicate by sending messages between each other, and semaphores to synchronize this communication. Tasks in FreeRTOS can be in one of four states: running, ready, blocked, or suspended. The FreeRTOS code handles task creation, scheduling, and maintenance using around 9,000 lines of code, with additional hardware-dependent code for the specific microcontroller.
FreeRTOS
- 1. FreeRTOS Open source real-time operating software
- 2. What is a real-time operating system? Real-time systems are designed to do something within a certain amount of time. If it does something right, but not within this amount of time, it is a failure.
- 3. What is a real-time operating system? Multitasking Scheduler Decides which task has to run Preemptive scheduling The task that is running can be interrupted by the scheduler when a higher-priority task needs to run. Cooperative scheduling The task decides when it has to stop. Preemptive scheduling is what we need for a real-time system.
- 4. Multitasking in FreeRTOS Different possibilities for scheduling the tasks on FreeRTOS: Round-Robin scheduling - Every task has the same priority. - Every task is given a fixed time to execute. - When time is over, the current task is preempted and the next ready task executes. Fixed Priority scheduling - A priority level is given to every created task. - The highest priority task executes, but is given a fixed time period. - When time is over, the current task is preempted and the next highest priority ready task executes.
- 5. Tasks in FreeRTOS In a multitasking environment, the tasks can have 4 different states: Running Ready Blocked Suspended The task is using the processor and is executing its code. The task is ready to be executed, and is waiting for the processor. The task is waiting for a time-related event or an external event. The task is not waiting for the processor.
- 6. Communication between tasks In FreeRTOS, tasks use queues to send data to each other: Message is placed in the memory by the emitting task. Message is recovered in the memory by the receiving task. We use binary semaphores to synchronize the communication: Acts like a flag that is going to inform the receiving task that the message is available. Queue
- 7. Architecture of FreeRTOS 50% 40% 10% FreeRTOS’s code Tasks Creating, scheduling and maintaining the tasks Hardware-dependent code depends on the microcontroller you are using Communication Between tasks Around 9000 lines of code