IMPORTANT! Notes on using this ARM Cortex-M4F demoPlease read all the following points before using this RTOS port.See also the FAQ My application does not run, what could be wrong?
The Atmel Studio project that builds the SAM4E-EK RTOS demo is located in the FreeRTOS/Demo/CORTEX_M4_ATSAM4E_Atmel_Studio directory. Note: The Atmel Studio project references files from multiple directories within the FreeRTOS and FreeRTOS+ directory trees, so will only build from this directory. FunctionalityThe constant mainCREATE_SIMPLE_BLINKY_DEMO_ONLY, which is defined at the top of main.c, is used to switch between a simple 'blinky' style starter project and the more comprehensive application that includes the additional FreeRTOS+ command line, networking and FAT file system components.
When mainCREATE_SIMPLE_BLINKY_DEMO_ONLY is set to 1When mainCREATE_SIMPLE_BLINKY_DEMO_ONLY is set to 1 main() calls main_blinky(). main_blinky() creates a very simple example that uses one software timer, one queue and two tasks.
When mainCREATE_SIMPLE_BLINKY_DEMO_ONLY is set to 0When mainCREATE_SIMPLE_BLINKY_DEMO_ONLY is set to 0 main() calls main_full(). main_full() creates an interactive test and demo application that creates numerous RTOS tasks and software timers, and includes network connectivity.If ipconfigUSE_DHCP is set to 1 in FreeRTOSIPConfig.h then the SAM4E-EK must be connected to a network that includes a DHCP server. If ipconfigUSE_DHCP is set to 0 in FreeRTOSIPConfig.h then the demo will use the static IP address configured by the constants configIP_ADDR0 to configIP_ADDR3 which are defined in FreeRTOSConfig.h (rather than FreeRTOSIPConfig.h). In each case the IP address used will be displayed on the LCD after it has been obtained. Static IP addresses must be compatible with the network to which they are being connected. This will be ensured if the first three octets of the configured IP address match the first three octets of other IP addresses already on the network. The MAC address is configured using the constants configMAC_ADDR0 to configMAC_ADDR5, which are also defined in FreeRTOSConfig.h. Each node connected to the network must use a unique MAC address. Functionality included in the demo:
Building and debugging the demo application with Atmel Studio
Configuration and Usage DetailsARM Cortex-M4 FreeRTOS port specific configurationConfiguration items specific to this demo are contained in FreeRTOS/Demo/CORTEX_M4_ATSAM4E_Atmel_Studio/src/config/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 Atmel SAM4 ARM Cortex-M4 microcontrollers, the lowest priority you can specify is in fact 15 - 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, as they are in the provided demo. 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.
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 portEND_SWITCHING_ISR() can be used to request a context switch from within an interrupt service routine.Note that portEND_SWITCHING_ISR() will leave interrupts enabled. The following source code snippet is provided as an example. The interrupt uses a semaphore to synchronise with a task (not shown), and calls portEND_SWITCHING_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 semaphore is used for this purpose. Note lHigherPriorityTaskWoken is initialised to zero. */ 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 ); } 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 allocationSource/Portable/MemMang/heap_4.c is included in the ARM Cortex-M4 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.MiscellaneousNote that vPortEndScheduler() has not been implemented.
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