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STM32F051 ARM Cortex-M0 Demo
Using the IAR development tools
[RTOS Ports]


The project described on this page demonstrates the FreeRTOS ARM Cortex-M0 IAR port. It is configured to run on the STM320518-EVAL evaluation board, which is fitted with an STM32F051 microcontroller.

The project can be configured to create either a basic blinky style demo, or a more comprehensive test and demo application that includes some of the FreeRTOS standard demo tasks.

FreeRTOS kernel aware debugger used with the IAR compiler
Screen shot of the FreeRTOS state viewer plug-in
that ships with the IAR IDE as standard.

Note: If this project fails to build then it is likely the version of IAR Embedded Workbench being used is too old. If this is the case, then it is also likely that the project file has been (silently) corrupted and will need to be restored to its original state before it can be built even with an updated IAR version.

IMPORTANT! Notes on using the IAR ARM Cortex-M0 Demo

Please read all the following points before using this RTOS port.

  1. Source Code Organisation
  2. The Demo Application
  3. RTOS Configuration and Usage Details
See also the FAQ My application does not run, what could be wrong?

Source Code Organisation

The FreeRTOS download contains the source code for all the FreeRTOS ports, so includes many more files than are needed by this demo. See the Source Code Organization section for a description of the downloaded files and information on creating a new project.

The IAR EWARM workspace for the FreeRTOS STM32F0 demo application is called RTOSDemo.eww, and is located in the FreeRTOS/Demo/CORTEX_M0_STM32F0518_IAR directory. Note that the workspace was created prior to STM32F0 support being included in EWARM, and as such, the project is configured to use a generic ARM Cortex-M0 core, and the instructions provided on this page describe the separate ST-Link utility being used to program the microcontroller flash memory.

The Demo Application

Demo application hardware set up

The demo uses the LEDs that are integrated onto the STM320518-EVAL board, so no hardware setup is required.

Building and running the demo application

The single RTOSDemo project can be configured to run a simple blinky style project, or a more comprehensive test and demo application. The mainCREATE_SIMPLE_BLINKY_DEMO_ONLY setting at the top of main.c is used to select between the two. Set mainCREATE_SIMPLE_BLINKY_DEMO_ONLY to one to create the basic Blinky style demo. Set mainCREATE_SIMPLE_BLINKY_DEMO_ONLY to 0 to create the more comprehensive test and demo application.
  1. Open FreeRTOS/Demo/CORTEX_M0_STM32F0518_IAR/RTOSDemo.eww in the IAR Embedded Workbench IDE.

  2. Set the mainCREATE_SIMPLE_BLINKY_DEMO_ONLY constant to generate the required demo functionality (as noted above), before building the project.

  3. Power up the STM320518-EVAL board, then connect a USB cable between the USB port labelled ST-LINK/V2 (SN3) and the host computer.

  4. Open FreeRTOS/Demo/CORTEX_M0_STM32F0518_IAR/Debug/RTOSDemo.bin in the ST-LINK utility program (a copy of which is provided on the CD that comes with the STM320518-EVAL hardware), then program the microcontroller flash memory. Later versions of the IAR Embedded Workbench will probably have the capability of programming the flash memory from within the IAR IDE, removing the need to use the separate ST-LINK utility.

  5. Select "Disconnect" from the ST-LINK utility's "Target" menu. A debug session cannot be started from the IAR IDE while the ST-LINK utility is connected to the hardware.

  6. Back in the IAR Embedded Workbench IDE - select "Debug without Downloading" from the IDE's "Project" menu to start a debug session.

Functionality with mainCREATE_SIMPLE_BLINKY_DEMO_ONLY set to 1

Setting mainCREATE_SIMPLE_BLINKY_DEMO_ONLY to 1 results in main() calling main_blinky(). main_blinky() sets up a very simple demo, as described below.
  • The main_blinky() Function:

    main_blinky() creates one queue, and two tasks. It then starts the scheduler.

  • The Queue Send Task:

    The queue send task is implemented by the prvQueueSendTask() function in main_blinky.c. prvQueueSendTask() sits in a loop that causes it to repeatedly block for 200 milliseconds, before sending the value 100 to the queue that was created within main_blinky(). Once the value is sent, the task loops back around to block for another 200 milliseconds.

  • The Queue Receive Task:

    The queue receive task is implemented by the prvQueueReceiveTask() function in main_blinky.c. prvQueueReceiveTask() sits in a loop where it repeatedly blocks on attempts to read data from the queue that was created within main_blinky(). When data is received, the task checks the value of the data, and if the value equals the expected 100, toggles LED LD1. The 'block time' parameter passed to the queue receive function specifies that the task should be held in the Blocked state indefinitely to wait for data to be available on the queue. The queue receive task will only leave the Blocked state when the queue send task writes to the queue. As the queue send task writes to the queue every 200 milliseconds, the queue receive task leaves the Blocked state every 200 milliseconds, and therefore toggles LED LD1 every 200 milliseconds.

Functionality with mainCREATE_SIMPLE_BLINKY_DEMO_ONLY set to 0

Setting mainCREATE_SIMPLE_BLINKY_DEMO_ONLY to 0 results in main() calling main_full(). main_full() sets up a more comprehensive test and demo application, as described below.
  • The main_full() Function:

    main_full() creates a set of standard demo tasks, some application specific test tasks, and a timer. It then starts the scheduler.

  • The "Reg Test" Tasks:

    These fill the registers with known values, then check that each register maintains its expected value for the lifetime of the task. Each task uses a different set of values. The reg test tasks execute with a very low priority, so get preempted very frequently. A register containing an unexpected value is indicative of an error in the context switching mechanism.

  • The "Check" software Timer:

    The check software timer period is initially set to three seconds. Its callback function checks that all the standard demo tasks, and the register check tasks, are not only still executing, but are executing without reporting any errors. If the check timer callback discovers that a task has either stalled, or reported an error, then it changes the period of the check timer from the initial three seconds, to just 200ms. The callback function also toggles LED LD4 each time it is called. This provides a visual indication of the system status: If LED LD4 toggles every three seconds, then no issues have been discovered. If the LED toggles every 200ms, then an issue has been discovered with at least one task.

RTOS Configuration and Usage Details

Interrupt service routines

Interrupt service routines that cause a context switch have no special requirements. The macro portEND_SWITCHING_ISR() can be used to request a context switch from within an ISR.

Note that portEND_SWITCHING_ISR() will leave interrupts enabled.

A dummy interrupt handler called Dummy_IRQHandler() is provided at the end of main.c as a reference implementation. Dummy_IRQHandler() is also replicated below.

void Dummy_IRQHandler(void)
long lHigherPriorityTaskWoken = pdFALSE;

    /* Clear the interrupt if necessary. */

    /* This interrupt does nothing more than demonstrate how to synchronise a
    task with an interrupt.  A semaphore is used for this purpose.  Note
    lHigherPriorityTaskWoken is initialised to zero. Only FreeRTOS API functions
    that end in "FromISR" can be called from an ISR! */
    xSemaphoreGiveFromISR( xTestSemaphore, &lHigherPriorityTaskWoken );

    /* If there was a task that was blocked on the semaphore, and giving the
    semaphore caused the task to unblock, and the unblocked task has a priority
    higher than the current Running state task (the task that this interrupt
    interrupted), then lHigherPriorityTaskWoken will have been set to pdTRUE
    internally within xSemaphoreGiveFromISR().  Passing pdTRUE into the
    portEND_SWITCHING_ISR() macro will result in a context switch being pended to
    ensure this interrupt returns directly to the unblocked, higher priority,
    task.  Passing pdFALSE into portEND_SWITCHING_ISR() has no effect. */
    portEND_SWITCHING_ISR( lHigherPriorityTaskWoken );

Note that the following lines are included in FreeRTOSConfig.h.

	#define vPortSVCHandler      SVC_Handler
	#define xPortPendSVHandler   PendSV_Handler
	#define xPortSysTickHandler  SysTick_Handler
These definitions map the FreeRTOS kernel interrupt handler function names onto the CMSIS interrupt handler functions names - and in so doing, allow the ST or IAR provided linker scripts and start up files to be used without modification.

Attention please!: See the page dedicated to setting interrupt priorities on ARM Cortex-M devices. Remember that ARM Cortex-M cores use numerically low priority numbers to represent HIGH priority interrupts. This can seem counter-intuitive and is easy to forget! If you wish to assign an interrupt a low priority do NOT assign it a priority of 0 (or other low numeric value) as this will result in the interrupt actually having the highest priority in the system. Also, do not leave interrupt priorities unassigned, as by default they will have a priority of 0 and therefore the highest priority possible.

RTOS port specific configuration

Configuration items specific to these demos are contained in FreeRTOS/Demo/CORTEX_M0_STM32F0518_IAR/FreeRTOSConfig.h. The constants defined in FreeRTOSConfig.h can be edited to meet the needs of your application. In particular -
  • configTICK_RATE_HZ

    This sets the frequency of the RTOS tick interrupt. The supplied value of 1000Hz is useful for testing the RTOS kernel functionality, but is faster than most applications require. Lowering this value will improve efficiency.

Each port #defines 'BaseType_t' to equal the most efficient data type for that processor. This port defines BaseType_t to be of type long.

Note that vPortEndScheduler() has not been implemented.

Switching between the pre-emptive and co-operative RTOS kernels

Set the definition configUSE_PREEMPTION within FreeRTOS/Demo/CORTEX_M0_STM32F0518_IAR/FreeRTOSConfig.h to 1 to use pre-emption or 0 to use co-operative.

Memory allocation

Source/Portable/MemMang/heap_2.c is included in the ARM Cortex-M0 demo application project to provide the memory allocation required by the RTOS kernel. Please refer to the Memory Management section of the API documentation for full information.

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