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
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.
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.
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
The main_blinky() Function:
main_blinky() creates one queue, and two tasks. It then starts the
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.
Some of the created tasks are from the set of standard demo
tasks, while others are specific
to this demo. Standard demo tasks are used by all FreeRTOS ports and demo applications.
They have no functional purpose, and exist just to demonstrate how to use the FreeRTOS API,
and test the FreeRTOS implementation.
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
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.
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
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
are equivalents that are defined using just the 6 priority bits implemented in the XMC4000
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
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 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.
long lHigherPriorityTaskWoken = pdFALSE;
/* Clear the interrupt if necessary. */
/* 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
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.
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
Note that vPortEndScheduler() has not been implemented.
Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2013 Real Time Engineers Ltd.
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