FreeRTOS V8.2.1 定制与配置指南

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"FreeRTOS V8.2.1的函数API手册是一份详细的PDF文档，包含目录，专门介绍这个实时操作系统的核心功能和调用接口。" FreeRTOS 是一个流行的、开源的实时操作系统（RTOS），主要设计用于微控制器和其他资源有限的嵌入式系统。它提供了一套高效的任务调度、内存管理、同步机制和中断处理等功能，以实现高效的多任务环境。在FreeRTOS V8.2.1版本中，开发者可以利用API函数来创建、管理和控制操作系统的行为。 FreeRTOS 的自定义是通过配置文件`FreeRTOSConfig.h`来完成的。每个基于FreeRTOS的应用程序都需要在预处理器的包含路径中有一个`FreeRTOSConfig.h`文件。这个文件是针对具体应用定制的，而不是针对RTOS本身，因此应该放置在应用程序的目录下，而不是RTOS内核源代码目录中。配置选项允许开发者根据项目需求调整内核的行为。例如，`configUSE_PREEMPTION`是一个关键的配置常量，它的值为1表示启用抢占式调度，即高优先级任务可以打断低优先级任务的执行；如果设置为0，则系统将采用合作式调度，任务只有在主动让出CPU时才会切换。在`FreeRTOSConfig.h`中，通常会包含其他跨应用程序所需的头文件。例如，`#include "something.h"`可能代表了特定项目中需要的一些通用定义或函数声明。示例中的配置文件定义还包括了`configUSE_PRIORITY_INHERITANCE`，这控制了优先级继承特性。当一个拥有较低优先级的任务持有高优先级的任务正在等待的资源时，该特性会暂时提升低优先级任务的优先级，以防止高优先级任务被阻塞。此外，`configTICK_RATE_HZ`定义了系统滴答的频率，即每秒发生的定时器中断次数，这直接影响了任务调度的精度。其他配置选项如`configMINIMAL_STACK_SIZE`定义了最小任务堆栈大小，`configTOTAL_HEAP_SIZE`则设定了总的堆内存大小。 `FreeRTOSConfig.h`文件是FreeRTOS应用的核心组成部分，通过合理的配置，开发者可以优化系统性能，满足不同应用场景的需求。购买FreeRTOS参考手册可以获取更全面的API函数和配置常量的描述，这对于深入理解和有效利用FreeRTOS至关重要。

This implementation:

Can be used even when the application repeatedly deletes tasks, queues, semaphores, mutexes,

etc., with the caveat below regarding memory fragmentation.

Should not be used if the memory being allocated and freed is of a random size. For example:

If an application dynamically creates and deletes tasks, and the size of the stack allocated

to the tasks being created is always the same, then heap2.c can be used in most cases.

However, if the size of the stack allocated to the tasks being created was not always the

same, then the available free memory might become fragmented into many small blocks,

eventually resulting in allocation failures. heap_4.c would be a better choise in this case.

If an application dynamically creates and deletes queues, and the queue storage area is

the same in each case (the queue storage area is the queue item size multiplied by the

length of the queue), then heap_2.c can be used in most cases. However, if the queue

storage area were not the same in each case, then the available free memory might

become fragmented into many small blocks, eventually resulting in allocation failures.

heap_4.c would be a better choise in this case.

The application called pvPortMalloc() and vPortFree() directly, rather than just indirectly

through other FreeRTOS API functions.

Could possible result in memory fragmentation problems if your application queues, tasks,

semaphores, mutexes, etc. in an unpredictable order. This would be unlikely for nearly all

applications but should be kept in mind.

Is not deterministic - but is much more efficient that most standard C library malloc

implementations.

heap_2.c is suitable for most small real time systems that have to dynamically create tasks.

heap_3.c

This implements a simple wrapper for the standard C library malloc() and free() functions that will, in

most cases, be supplied with your chosen compiler. The wrapper simply makes the malloc() and free()

functions thread safe.

This implementation:

Requires the linker to setup a heap, and the compiler library to provide malloc() and free()

implementations.

Is not deterministic.

Will probably considerably increase the RTOS kernel code size.

Note that the configTOTAL_HEAP_SIZE setting in FreeRTOSConfig.h has no effect when heap_3 is

used.

heap_4.c

This scheme uses a first fit algorithm and, unlike scheme 2, does combine adjacent free memory blocks

into a single large block (it does include a coalescence algorithm).

The total amount of available heap space is set by configTOTAL_HEAP_SIZE - which is defined in

FreeRTOSConfig.h.

The xPortGetFreeHeapSize() API function returns the total amount of heap space that remains

unallocated (allowing the configTOTAL_HEAP_SIZE setting to be optimised), but does not provided

information on how the unallocated memory is fragmented into smaller blocks.

This implementation:

Can be used even when the application repeatedly deletes tasks, queues, semaphores, mutexes,

etc..

Is much less likely than the heap_2 implementation to result in a heap space that is badly

fragmented into multiple small blocks - even when the memory being allocated and freed is of

random size.

Is not deterministic - but is much more efficient that most standard C library malloc

implementations.

heap_4.c is particularly useful for applications that want to use the portable layer memory allocation

schemes directly in the application code (rather than just indirectly by calling API functions that

themselves call pvPortMalloc() and vPortFree()).

heap_5.c

This scheme uses the same first fit and memory coalescence algorithms as heap_4, and allows the heap

to span multiple non adjacent (non-contiguous) memory regions.

Heap_5 is initialised by calling vPortDefineHeapRegions(), and

cannot be used

until after

vPortDefineHeapRegions() has executed. Creating an RTOS object (task, queue, semaphore, etc.) will

implicitly call pvPortMalloc() so it is essential that, when using heap_5, vPortDefineHeapRegions() is

called before the creation of any such object.

vPortDefineHeapRegions() takes a single parameter. The parameter is an array of HeapRegion_t

structures. HeapRegion_t is defined in portable.h as

typedef struct HeapRegion

{

/* Start address of a block of memory that will be part of the heap.*/

uint8_t *pucStartAddress;

/* Size of the block of memory. */

size_t xSizeInBytes;

Stack Usage and Stack Overflow Checking

[

More Advanced

]

Stack Usage

Each task maintains its own stack. The memory used by the task stack is allocated automatically when

the task is created, and dimensioned by a parameter passed to the xTaskCreate() API function. Stack

overflow is a very common cause of application instability. FreeRTOS therefore provides two optional

mechanisms that can be used to assist in the detection and correction of just such an occurrence. The

option used is configured using the configCHECK_FOR_STACK_OVERFLOW configuration constant.

Note that these options are only available on architectures where the memory map is not segmented.

Also, some processors could generate a fault or exception in response to a stack corruption before the

RTOS kernel overflow check can occur. The application must provide a stack overflow hook function if

configCHECK_FOR_STACK_OVERFLOW is not set to 0. The hook function must be called

vApplicationStackOverflowHook(), and have the prototype below:

void vApplicationStackOverflowHook( TaskHandle_t xTask,

signed char *pcTaskName );

The xTask and pcTaskName parameters pass to the hook function the handle and name of the

offending task respectively. Note however, depending on the severity of the overflow, these parameters

could themselves be corrupted, in which case the pxCurrentTCB variable can be inspected directly.

Stack overflow checking introduces a context switch overhead so its use is only recommended during

the development or testing phases.

Stack Overflow Detection - Method 1

It is likely that the stack will reach its greatest (deepest) value after the RTOS kernel has swapped the

task out of the Running state because this is when the stack will contain the task context. At this point

the RTOS kernel can check that the processor stack pointer remains within the valid stack space. The

stack overflow hook function is called if the stack pointer contain a value that is outside of the valid stack

range.

This method is quick but not guaranteed to catch all stack overflows. Set

configCHECK_FOR_STACK_OVERFLOW to 1 to use this method only.

Stack Overflow Detection - Method 2

When a task is first created its stack is filled with a known value. When swapping a task out of the

Running state the RTOS kernel can check the last 16 bytes within the valid stack range to ensure that

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