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Infineon XMC4500 ARM Cortex-M4F Demo
Using IAR EWARM and Keil MDK development tools
[RTOS Ports]
Introduction
This page documents a demo application that targets the Infineon XMC4000 Hexagon Development Kit CPU board, which is fitted with an XMC4500 microcontroller. Build projects are provided for both the IAR Embedded Workbench and the Keil uVision development tools.Note: If this project fails to build using the IAR tools 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.
The FreeRTOS ARM Cortex-M4F port supports a full interrupt nesting model, and never completely disable interrupts. The port can only be used with the ARM Cortex-M4's hardware floating point unit turned on, and with the IAR or Keil project settings configured to generate floating point instructions. The demos described on this page are supplied pre-configured with these required settings. Cortex-M4 devices that don't include a floating point unit should not use the ARM Cortex-M4F port, but instead use the FreeRTOS ARM Cortex-M3 port layer.
Using a compile time option (described below), the projects can be configured to create either a basic blinky style demo, or a more comprehensive test and demo application that includes tasks that exercise the interrupt nesting behaviour.
Note that, if the Keil project is selected, Keil MDK version 4.2.2 or above is required, to which (at the time of writing) a patch needs to be supplied to provide integrated XMC4000 support. The no_allow_fpreg_for_nonfpdata compiler option must also be used, again, the demo supplied is pre-configured with this setting.
IMPORTANT! Notes on using the FreeRTOS IAR and Keil XMC4000 demo projects
Please read all the following points before using these RTOS projectsSee also the FAQ My application does not run, what could be wrong?
Source Code Organisation
The FreeRTOS zip file download contains source code for all the FreeRTOS ports, and every demo application project. It therefore contains many more files than are required to build and run the Infineon XMC4500 demo. See the Source Code Organization section for a description of the downloaded files, and information on creating a new project.The IAR Embedded Workbench for ARM demo project workspace is called RTOSDemo.eww, and is located in the FreeRTOS/Demo/CORTEX_M4F_Infineon_XMC4500_IAR directory of the official FreeRTOS .zip file download.
The Keil uVision demo project is called RTOSDemo.uvproj, and is located in the FreeRTOS/Demo/CORTEX_M4F_Infineon_XMC4500_Keil directory of the official FreeRTOS .zip file download.
The Infineon XMC4500 Demo Application
Both the IAR and Keil RTOSDemo projects provide two configurations. They can be configured as a simple blinky style project, or a more comprehensive test and demo application. The mainCREATE_SIMPLE_BLINKY_DEMO_ONLY definition, located at the top of the respective main.c files, is used to switch between the two at compile time.
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 RTOS 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 the LED. 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 the LED every 200 milliseconds.
Functionality with mainCREATE_SIMPLE_BLINKY_DEMO_ONLY set to 0
This demo application demonstrates:
- Floating point context switching.
- Malloc failed and stack overflow hook functions. main.c also contains Tick and Idle hook functions, but FreeRTOSConfig.h is not configured to use them. See the comments in the implementation of the functions in main.c.
- Software timers.
- Semaphores.
- Mutexes.
- Queues.
main() creates 43 tasks before starting the RTOS scheduler. The demo then dynamically and continuously creates and deletes a further two tasks while it is running.
Application specific "register test" tasks are created in addition to the standard demo tasks. These start by filling all the generic, and all the floating point registers, with known values. The tasks then repeatedly check that each register maintains the value written to it for the lifetime of the tasks. The register check tasks run at the idle priority, so will exit and re-enter the Running state frequently. The two register check tasks each fill the CPU registers with different values, and a register containing an unexpected value is symptomatic of an error in the context switching mechanism.
A 'check' software timer is created that periodically inspects the standard demo tasks, and register test tasks, to ensure all the tasks are functioning as expected. The check software timer's callback function toggles the single user LED on the XMC4500 Hexagon development kit CPU board. This gives a visual feedback of the system health. If the LED is toggling every 3 seconds, then the check software timer has not discovered any problems. If the LED is toggling every 200 milliseconds, then the check software timer has discovered a problem in one or more tasks.
Hardware set up
The demo uses the LED that is soldered directly onto the CPU board PCB, so no hardware set up is required.
Building and executing the demo application
- Set the mainCREATE_SIMPLE_BLINKY_DEMO_ONLY constant to generate the required demo functionality, as noted above.
- Ensure the target hardware is connected to the host computer using a suitable interface. The IAR project was created and tested using a J-Link. The Keil project was created and testing using a ULINK ME.
- Optionally open the RTOSDemo.eww IAR workspace from within the Embedded Workbench IDE, or the RTOSDemo.uvproj project from within the Keil uVision IDE.
- Select "Build" or "Make" from the IDE's "Project" menu (or press F7). The project should build without any warnings or errors.
- After the project has built, press CTRL+D if using IAR, or CTRL+F5 is using Keil to program the microcontroller's flash memory, and start a debug session. The debugger will then start running and break on entry to the main() function.
RTOS Configuration and Usage Details
Cortex-M4F FreeRTOS port specific configuration
Configuration items specific to this demo are contained in FreeRTOS/Demo/CORTEX_M4F_Infineon_XMC4500_IAR/FreeRTOSConfig.h or FreeRTOS/Demo/CORTEX_M4F_Infineon_XMC4500_Keil/FreeRTOSConfig.h for the IAR and Keil projects respectively. The constants defined in this file can be edited to suit 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 need. Lowering the frequency will improve efficiency.
-
configKERNEL_INTERRUPT_PRIORITY and configMAX_SYSCALL_INTERRUPT_PRIORITY
See the RTOS kernel configuration documentation for full information on these configuration constants.
-
configLIBRARY_LOWEST_INTERRUPT_PRIORITY and configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY
Whereas configKERNEL_INTERRUPT_PRIORITY and configMAX_SYSCALL_INTERRUPT_PRIORITY are full eight bit shifted values, defined to be used as raw numbers directly in the ARM Cortex-M4F NVIC registers, configLIBRARY_LOWEST_INTERRUPT_PRIORITY and configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY are equivalents that are defined using just the 6 priority bits implemented in the XMC4000 NVIC. These values are provided because the CMSIS library function NVIC_SetPriority() requires the unshifted 6 bit format.
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 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 Infineon XMC4000 ARM Cortex-M4 microcontrollers, the lowest priority you can specify is in fact 63 - 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 six 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 'portBASE_TYPE' to equal the most efficient data type for that processor. This port defines portBASE_TYPE to be of type long.
Interrupt service routines
Unlike 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.
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 FreeRTOS
FreeRTOS requires exclusive use of the SysTick and PendSV interrupts. SVC number #0 is also used.Switching between the pre-emptive and co-operative RTOS kernels
Set 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 options
As 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 allocation
Source/Portable/MemMang/heap_2.c is included in the ARM Cortex-M4F 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.Miscellaneous
Note that vPortEndScheduler() has not been implemented.
Any and all data, files, source code, html content and documentation included in the FreeRTOSTM distribution or available on this site are the exclusive property of Real Time Engineers Ltd.. See the files license.txt (included in the distribution) and this copyright notice for more information. FreeRTOSTM and FreeRTOS.orgTM are trade marks of Real Time Engineers Ltd.