This page describes the FreeRTOS demo application for the STMicroelectronics STM32 ARM Cortex-M3 microcontroller. The demo uses the IAR Embedded Workbench development tools for ARM, and is preconfigured to run on the STM32 evaluation board from ST (instructions are provided should you wish to use an alternative development board). The evaluation board is fitted with an STM32F103VB microcontroller that contains 128KBytes of on board flash and 20KBytes of on board RAM. The STM32F103VB also includes both USB and CANbus peripherals.
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 STM32 ARM Cortex-M3 DemoPlease read all the following points before using this RTOS port.
My application does not run, what could be wrong?
Source Code OrganisationThe FreeRTOS download includes the source code for all the FreeRTOS ports and therefore contains many more files than are required for this demo. See the Source Code Organization section for a description of the downloaded files and information on creating a new project.
The IAR workspace file for the STM32F103 demo is called RTOSDemo.eww and is located in the FreeRTOS/Demo/CORTEX_STM32F103_IAR directory.
The Demo Application
Demo application hardware setupThe demo application includes an interrupt driven UART test where one task transmits characters that are then received by another task. For correct operation of this functionality a loopback connector must be fitted to the UART00 connector of the STM32 evaluation board (pins 2 and 3 must be connected together on the 9Way connector).
The demo application uses the LEDs and display built onto the prototyping board so no other hardware setup is required.
A J-Link USB JTAG interface is used to interface the host PC with the target.
Building and running the demo application
FunctionalityThe demo application creates 24 persistent tasks, and periodically dynamically creates and destroys another 4. These tasks consist predominantly of the standard demo application tasks (see the demo application section for details of the individual tasks).
The following tasks and tests are created in addition to the standard demo tasks:
When executing correctly the demo application will behave as follows:
RTOS port specific configurationConfiguration items specific to these demos are contained in FreeRTOS/Demo/CORTEX_STM32F103_IAR/FreeRTOSConfig.h. The constants defined in this file can be edited to suit your application. In particular –
Attention please!: Remember that ARM Cortex-M3 cores use numerically low priority numbers to represent HIGH priority interrupts, which 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 can result in the interrupt actually having the highest priority in the system – and therefore potentially make your system crash if this priority is above configMAX_SYSCALL_INTERRUPT_PRIORITY.
The lowest priority on a ARM Cortex-M3 core is in fact 255 – however different ARM Cortex-M3 vendors implement a different number of priority bits and supply library functions that expect priorities to be specified in different ways. For example, on the STM32 the lowest priority you can specify in an ST driver library call is in fact 15 – and the highest priority you can specify is 0. This is defined by the constant configLIBRARY_KERNEL_INTERRUPT_PRIORITY in FreeRTOSConfig.h.
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.
Interrupt service routinesUnlike most ports, interrupt service routines that cause a context switch have no special requirements and can be written as per the compiler documentation. 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.
Switching between the pre-emptive and co-operative RTOS kernelsSet the definition configUSE_PREEMPTION within FreeRTOS/Demo/CORTEX_STM32F103_IAR/FreeRTOSConfig.h to 1 to use pre-emption or 0 to use co-operative.
Compiler optionsAs with all the ports, it is essential that the correct compiler options are used. The best way to ensure this is to base your application on the provided demo application files.
Memory allocationSource/Portable/MemMang/heap_2.c is included in the ARM Cortex-M3 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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