Hardware set up - MikroC Pro for ARM projectThe MikroC project is pre-configured to run on a CEC1302 Clicker board, and uses the LED built onto that hardware.
FunctionalityThe project provides two RTOS demo applications. A simple blinky style project that demonstrates low power tickless functionality, and a more comprehensive test and demo application. The configCREATE_LOW_POWER_DEMO setting, which is defined in FreeRTOSConfig.h, is used to select between the two.
Functionality with configCREATE_LOW_POWER_DEMO set to 1When configCREATE_LOW_POWER_DEMO is set to 1 main() calls main_low_power(), which creates a very simple demo as follows:
Observed behaviour when configCREATE_LOW_POWER_DEMO is set to 1Both tasks spend most of their time in the Blocked state, during which periods the RTOS tick is turned off, and the ARM Cortex-M4F is placed into a low power state. Every 1000ms the MCU will come out of the low power state, turn the LED on, return to the low power state for 10ms, before leaving the low power state again to turn the LED off. This will be observed as a short blip on the LED every 1000ms.
RTOS implementation when configCREATE_LOW_POWER_DEMO is set to 1The demo is provided with a low power tickless implementation that uses the CEC1302 hibernation timer to generate the RTOS tick interrupt.This CEC1302 specific tickless implementation includes the same configPRE_SLEEP_PROCESSING() and configPOST_SLEEP_PROCESSING() macros that are described on the page that documents the generic Cortex-M tickless implementation. The pre sleep macro can be defined to take additional application specific actions to improve energy efficiency before entering the low power state, and the post sleep macro can be defined to reverse any of the actions taken by the pre sleep macro. For example, if the pre-sleep macro is defined to turn a peripheral off, and the post sleep macro is defined to turn the peripheral on again, then the peripheral will automatically be turned off prior to each entry into the sleep mode, and automatically turned back on again on each exit from the sleep mode.
Functionality with configCREATE_LOW_POWER_DEMO set to 0When configCREATE_LOW_POWER_DEMO is set to 0 main() calls main_full(), which creates a comprehensive test and demo application that demonstrates:
A 'check' task is created that periodically inspects the standard demo tasks to ensure all the tasks are functioning as expected. The check task toggles an LED (or increments the ulLED variable). This gives a visual feedback of the system health. If an LED is toggling every 3 seconds, then the check task has not discovered any problems. If the LED is toggling every 200 milliseconds, then the check task has discovered a problem in one or more tasks.
Building and executing the demo applicationUsing the uVision project with the GCC compiler
Using the uVision project with the ARM compiler
Using the MikroC Pro compiler for ARM and the Clicker hardwareCaution: The MikroC compiler will leave many temporary files throughout your project directory structure, the built in editor is not compatible with the formatting conventions used by the RTOS source files, and to allow the FreeRTOS source files to be built the FreeRTOS MikroC port layer #defines the 'const' keyword away to nothing.
RTOS Configuration and Usage Details
ARM Cortex-M4 FreeRTOS port specific configurationConfiguration items specific to this demo are contained in /FreeRTOS/Demo/CORTEX_M4F_CEC1302_Keil_GCC/FreeRTOSConfig.h. The constants defined in this file can be edited to suit your application. In particular -
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 - and therefore potentially make your system crash if this priority is above configMAX_SYSCALL_INTERRUPT_PRIORITY. Also, do not leave interrupt priorities unassigned, as by default they will have a priority of 0, and therefore the highest priority possible. The lowest priority on a ARM Cortex-M core is in fact 255 - however different ARM Cortex-M microcontroller manufacturers implement a different number of priority bits and supply library functions that expect priorities to be specified in different ways. For example, on Microchip CEC1302 ARM Cortex-M4 microcontrollers, the lowest priority you can specify is in fact 7 - this is defined by the constant configLIBRARY_LOWEST_INTERRUPT_PRIORITY in FreeRTOSConfig.h. The highest priority that can be assigned is always zero. It is also recommended to ensure that all priority bits are assigned as being preemption priority bits, and none as sub priority bits. 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.
Aggregated and disaggregated interruptsThe CEC1302 can route groups of interrupt sources to the same interrupt vector (aggregated interrupts), or route all interrupt sources to their own unique interrupt vector (disaggregated interrupts). The RTOS itself only uses ARM Cortex-M system interrupts, which are always routed to the standard ARM Cortex-M system vectors, but the demo application also makes use of btimer (basic timer) and htimer (hibernation timer) interrupts, both of which can be aggregated or disaggregated. In order to demonstrate both methods, the tickless low power demo is configured to use aggregated interrupts and the comprehensive demo is configured to use disaggregated interrupts (note the comprehensive demo uses disaggregated interrupts as the interrupt nesting test cannot function if all the timer interrupts are routed through the same vector).Interrupt service routinesUnlike many FreeRTOS ports, interrupt service routines that cause a context switch have no special requirements, and can be written as per the compiler documentation. The macro portYIELD_FROM_ISR() can be used to request a context switch from within an interrupt service routine.Note that portYIELD_FROM_ISR() will leave interrupts enabled. The following source code snippet is provided as an example. The interrupt uses a direct to task notification to synchronise with a task (not shown), and calls portYIELD_FROM_ISR() to ensure the interrupt returns directly to the task if the task has an equal or higher priority than the interrupted task. 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 task notification is used for this purpose. Note lHigherPriorityTaskWoken is initialised to zero. */ vTaskNotifyGiveFromISR( xHandlingTask, &xHigherPriorityTaskWoken ); /* If the notified task was blocked waiting for the notification, and the 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 vTaskNotifyGiveFromISR(). Passing pdTRUE into the portYIELD_FROM_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 portYIELD_FROM_ISR() has no effect. */ portYIELD_FROM_ISR( lHigherPriorityTaskWoken ); } Only FreeRTOS API functions that end in "FromISR" can be called from an interrupt service routine - and then only if the priority of the interrupt is less than or equal to that set by the configMAX_SYSCALL_INTERRUPT_PRIORITY configuration constant (or configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY).
Resources used by FreeRTOSFreeRTOS requires exclusive use of the SysTick and PendSV interrupts. SVC number #0 is also used.Switching between the pre-emptive and co-operative RTOS kernelsSet the definition configUSE_PREEMPTION within FreeRTOSConfig.h to 1 to use pre-emption or 0 to use co-operative. The full demo application may not execute correctly when the co-operative RTOS scheduler is selected.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 allocationconfigSUPPORT_STATIC_ALLOCATION and configSUPPORT_DYNAMIC_ALLOCATION are both set to 1, allowing RTOS objects to be created statically or dynamically. Source/Portable/MemMang/heap_4.c is used to provide the RAM required by dynamically allocated RTOS objects. Please refer to the Memory Management section of the API documentation for full information.MiscellaneousNote that vPortEndScheduler() has not been implemented.
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