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Lab2

  • Developing tasks in FreeRTOS

  • Name: Liu Jun

  • Number: 192050223

Questions

  1. What features of FreeRTOS do you remember?

    • Pre-emptive or co-operative operation
    • Very flexible task priority assignment
    • Flexible, fast and light weight task notification mechanism
    • Queues
    • Binary semaphores
    • Counting semaphores
    • Mutexes
    • Recursive Mutexes
    • Software timers
    • Event groups
    • Tick hook functions
    • Idle hook functions
    • Stack overflow checking
    • Trace recording
    • Task run-time statistics gathering
    • Optional commercial licensing and support
    • Full interrupt nesting model (for some architectures)
    • A tick-less capability for extreme low power applications
    • Software managed interrupt stack when appropriate (this can help save RAM)

  2. What are the differences between FreeRTOS, OpenRTOS and SafeRTOS?

    • The FreeRTOS open source license is designed to ensure:
      1. FreeRTOS can be used in commercial applications.
      2. FreeRTOS itself remains freely available to everybody.
      3. FreeRTOS users retain ownership of their intellectual property.
    • OpenRTOS is a commercially licensed version of FreeRTOS provided under license from Real Time Engineers Ltd. by a third party.
    • SafeRTOS shares the same usage model as FreeRTOS, but has been developed in accordance with the practices, procedures, and processes necessary to claim compliance with various internationally recognized safety related standards.

  3. Why do we need the vTaskStartScheduler() function? Starts the FreeRTOS scheduler running. Typically, before the scheduler has been started, main() (or a function called by main()) will be executing. After the scheduler has been started, only tasks and interrupts will ever execute. Starting the scheduler causes the highest priority task that was created while the scheduler was in the Initialization state to enter the Running state.

  4. Why do we need the xTaskCreate() function? Creates a new instance of a task. Each task requires RAM that is used to hold the task state (the task control block, or TCB), and used by the task as its stack. If a task is created using xTaskCreate() then the required RAM is automatically allocated from the FreeRTOS heap. If a task is created using xTaskCreateStatic() then the RAM is provided by the application writer, which results in two additional function parameters, but allows the RAM to be statically allocated at compile time. Newly created tasks are initially placed in the Ready state, but will immediately become the Running state task if there are no higher priority tasks that are able to run. Tasks can be created both before and after the scheduler has been started.