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  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2How to Install
    1. 2.1 Update the FreeRTOS Version in the TivaWare Directory
    2. 2.2 Adding FreeRTOS Hardware Driver Files for TM4C LaunchPads
  5. 3Architecture for TM4C FreeRTOS Examples
    1. 3.1 Proper Clock Configuration
    2. 3.2 How to use Hardware Interrupts Alongside the FreeRTOS Kernel
  6. 4Example Project Walkthroughs
    1. 4.1 Download and Import the Examples
    2. 4.2 Kernel Examples
      1. 4.2.1 Example: hello
      2. 4.2.2 Example: notify_example
      3. 4.2.3 Example: queue_example
      4. 4.2.4 Example: semaphore_example
      5. 4.2.5 Example: blinky_queue
      6. 4.2.6 Software Timer Examples
        1. 4.2.6.1 Example: timer_sw_oneshot
        2. 4.2.6.2 Example: timer_sw_periodic
        3. 4.2.6.3 Example: timer_sw_led_counter/timer_sw_rgb
    3. 4.3 ADC Examples
      1. 4.3.1 Example: adc_multi_channel
      2. 4.3.2 Example: adc_timer_trigger
    4. 4.4 Hardware Timer Examples
      1. 4.4.1 Example: timer_hw_oneshot
      2. 4.4.2 Example: timer_hw_periodic
      3. 4.4.3 Example: timer_hw_pwm
    5. 4.5 UART Example
      1. 4.5.1 Example: uart_thread_safe
    6. 4.6 Watchdog Example
      1. 4.6.1 Example: watchdog

4.2.4 Example: semaphore_example

This example is used to introduce the concept of a semaphore. A semaphore is a synchronization method used to control access to a common resource by multiple threads or tasks in a multitasking operating sytem. Three new APIs: xSemaphoreCreateBinary, xSemaphoreTake, and xSemaphoreGiveFromISR are utilized in this example. xSemaphoreCreateBinary is used to create a semaphore. A task uses the xSemaphoreTake API to enter a BLOCKed state and wait for the requested semaphore to be made available. For this example, pressing a switch on the LaunchPad board will trigger an interrupt and the associated ISR will release the semaphore using xSemaphoreGiveFromISR. Once the semaphore is received, the task is unblocked and toggles the on-board LED(s) before going back to the BLOCKed state to wait for the next semaphore.