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NXP LPC43xx ARM Cortex-M4F Demo
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mainCREATE_SIMPLE_LED_FLASHER_DEMO_ONLY setting
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Description
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| Set to 1 |
This creates a very simple example that creates three
standard demo "flash" tasks. Each of the three tasks toggles an
LED at a fixed but different frequency. LEDs LED3, LED2 and LED1
are used.
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| Set to 0 |
This is a very comprehensive demo that creates 46 tasks before
starting the RTOS scheduler. It then continuously creates and
deletes a further two tasks while the application is executing.
The demo includes a lot of queues, a software timer, and various different types of semaphore. The tasks consist mainly of the standard demo tasks. Application specific "register test" tasks are also created. 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 task. The tasks run at the idle priority, so will exit and re-enter the Running state often. The two register check tasks each use 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 LED LED0. This gives visual feedback of the system health. If LED LED0 is toggling every 3 seconds, then the check software timer has not discovered any problems. If LED LED0 is toggling every 200 milliseconds, then the check software timer has discovered a problem in one or more tasks. Like the simple flasher demo, the comprehensive demo creates the standard demo flash tasks, which toggle LEDs LED3, LED2 and LED1 at fixed but different frequencies. |
Hardware set up
The demo uses the LEDs that are soldered directly onto the Hitex PCB, so no hardware set up is required.
Building and executing the demo application
- Ensure the target hardware is connected to the host computer using a suitable interface. The project has been tested with both a ULINK2 and a ULINK ME.
- Open the M4.uvproj Keil project from within the Keil IDE.
- Select "Build" from the IDE's "Project" menu, or simply press F7. The project should build without any errors or warnings.
- When the build completes, select "Start/Stop Debug Session" from the IDE's "Debug" menu (or just press CTRL+F5) to program the microcontroller flash memory, and start a debug session. The execution will 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_M0_LPC43xx_Keil/M4/FreeRTOSConfig.h. 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 require. Lowering this value will improve efficiency.
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configKERNEL_INTERRUPT_PRIORITY and configMAX_SYSCALL_INTERRUPT_PRIORITY
See the RTOS kernel configuration documentation for full information on these configuration constants.
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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 exact equivalents, but defined using just the 5 priority bits available on the LPC4300. The CMSIS library function NVIC_SetPriority() requires the unshifted 5 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 vendors implement a different number of priority bits and supply library functions that expect priorities to be specified in different ways. For example, on LPC ARM Cortex-M microcontrollers, the lowest priority you can specify is in fact 31 - 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 five 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.
Core clock configuration
The demo runs the LPC4350 clock at 204MHz. To achieve this it is necessary for the functions that configure the parallel flash memory controller to execute out of RAM. The mapping of these functions is performed within the linker script itself (scatter file), and the code that steps the core clock up to 204MHz is contained in Hitex_fast_startup.c.Interrupt service routines
Unlike most 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.
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 RTOSDemo/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.
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