IntroductionThe project described on this page demonstrates the FreeRTOS ARM Cortex-M0 GCC port. It is configured to run on the LPC1114 version of the LPCXpresso board, using the free Eclipse based LPCXpresso IDE.Using a compile time option (described below), the project can be configured to either create a basic blinky style demo, or a more comprehensive test and demo application that includes tasks that exercise the interrupt nesting behaviour.
Screen shot of the FreeRTOS aware state viewer plug-in that ships with the LPCXpresso IDE as standard. Click the image to enlarge.
IMPORTANT! Notes on using the LPC1114 LPCXpresso ARM Cortex-M0 DemoPlease read all the following points before using this RTOS port.See also the FAQ My application does not run, what could be wrong?
Source Code OrganisationThe 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 FreeRTOS demo application is dependent on the CMSIS library, which is provided as a separate LPCXpresso project. The demo application project and the CMSIS project must both be imported into an LPCXpresso workspace. Both projects are located in subdirectories of the FreeRTOS/Demo/CORTEX_M0_LPC1114_LPCXpresso directory, and can be imported into LPCXpresso together. The Preparing the Eclipse Project section below contains important information on setting up the demo project directory, and importing the demo project into the LPCXpresso IDE.
The Demo ApplicationDemo application hardware set upThe demo uses the LED that is integrated onto the LPCXpresso board, so no hardware setup is required.
CreateProjectDirectoryStructure.bat must be executed before the LPCXpresso project is imported into the Eclipse workspace. CreateProjectDirectoryStructure.bat cannot be executed from within the LPCXpresso IDE.
Importing the demo application and CMSIS projects into the LPCXpresso Eclipse workspaceTo import the necessary projects into an existing or new Eclipse Workspace:
Building and running the demo applicationThe single RTOSDemo project provides two configurations. It can be configured as a simple blinky style project, or a more comprehensive test and demo application. The mainCREATE_SIMPLE_BLINKY_DEMO_ONLY setting in 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.
Functionality with mainCREATE_SIMPLE_BLINKY_DEMO_ONLY set to 1Setting mainCREATE_SIMPLE_BLINKY_DEMO_ONLY to 1 results in main() calling main_blinky(). main_blinky() sets up a very simple demo, as described below.
Functionality with mainCREATE_SIMPLE_BLINKY_DEMO_ONLY set to 0Setting 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.
RTOS Configuration and Usage DetailsInterrupt service routinesInterrupt 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. The interrupt nesting test tasks require that two timers are configured to generate interrupts. The interrupt service routines are defined in IntQueueTimer.c, and can be used as examples for application writers. They do not, however, directly demonstrate the use of FreeRTOS safe API functions (those that end in "FromISR"). Therefore, a dummy interrupt implementation called Dummy_IRQHandler() is provided at the end of main.c, and duplicated below.
void Dummy_IRQHandler(void) { long lHigherPriorityTaskWoken = pdFALSE; /* Clear the interrupt if necessary. */ Dummy_ClearITPendingBit(); /* 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_HandlerThese definitions map the FreeRTOS kernel interrupt handler function names onto the CMSIS interrupt handler functions names (or at least whatever is used in the unmodified vector table supplied by the compiler) - and in so doing, allow the Code Red provided linker script 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 configurationConfiguration items specific to these demos are contained in FreeRTOS/Demo/CORTEX_M0_LPC1114_LPCXpresso/RTOSDemo/Source/FreeRTOSConfig.h. The constants defined in FreeRTOSConfig.h can be edited to meet the needs of your application. In particular -
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 kernelsSet the definition configUSE_PREEMPTION within FreeRTOS/Demo/CORTEX_M0_LPC1114_LPCXpresso/RTOSDemo/Source/FreeRTOSConfig.h to 1 to use pre-emption or 0 to use co-operative.Memory allocationSource/Portable/MemMang/heap_1.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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