FreeRTOS动态内存分配管理heap_5示例

目录

• heap_5.c
• vPortDefineHeapRegions
• 常见问题

heap_5.c

heap5与heap4分配释放算法完全相同，只是heap5支持管理多块不连续的内存，本质是将多块不连续内存用链表串成一整块内存，再用heap4算法来分配释放。若使用heap5则在涉及到分配释放的函数调用时要先调用vPortDefineHeapRegions把多块不连续内存串成一块初始化。

vPortDefineHeapRegions

此函数原型

void vPortDefineHeapRegions( const HeapRegion_t * const pxHeapRegions )，

参数在portable.h中定义，如下

/* Used by heap_5.c. */
typedef struct HeapRegion
{
	uint8_t *pucStartAddress;//指向内存块首地址
	size_t xSizeInBytes;//此内存块大小
} HeapRegion_t;

比如有2块内存要用heap5管理，地址0x80000000，大小0x10000,地址0x90000000，大小0xa0000,则如下定义该结构体数组

 HeapRegion_t xHeapRegions[] =
 {
 	{ ( uint8_t * ) 0x80000000UL, 0x10000 },
 	{ ( uint8_t * ) 0x90000000UL, 0xa0000 }, 
 	{ NULL, 0 } 
 };

注意地址顺序要从小到大，最后要以{NULL，0}结尾(源码是以0做判断结束循环)
下面看初始化源码

void vPortDefineHeapRegions( const HeapRegion_t * const pxHeapRegions )
{
BlockLink_t *pxFirstFreeBlockInRegion = NULL, *pxPreviousFreeBlock;
size_t xAlignedHeap;
size_t xTotalRegionSize, xTotalHeapSize = 0;
BaseType_t xDefinedRegions = 0;
size_t xAddress;
const HeapRegion_t *pxHeapRegion;
	/* Can only call once! */
	configASSERT( pxEnd == NULL );
	pxHeapRegion = &( pxHeapRegions[ xDefinedRegions ] );
	while( pxHeapRegion->xSizeInBytes > 0 )
	{
		xTotalRegionSize = pxHeapRegion->xSizeInBytes;
		/* Ensure the heap region starts on a correctly aligned boundary. */
		xAddress = ( size_t ) pxHeapRegion->pucStartAddress;
		if( ( xAddress & portBYTE_ALIGNMENT_MASK ) != 0 )
		{
			xAddress += ( portBYTE_ALIGNMENT - 1 );
			xAddress &= ~portBYTE_ALIGNMENT_MASK;
			/* Adjust the size for the bytes lost to alignment. */
			xTotalRegionSize -= xAddress - ( size_t ) pxHeapRegion->pucStartAddress;
		}
		xAlignedHeap = xAddress;
		/* Set xStart if it has not already been set. */
		if( xDefinedRegions == 0 )
		{
			/* xStart is used to hold a pointer to the first item in the list of
			free blocks.  The void cast is used to prevent compiler warnings. */
			xStart.pxNextFreeBlock = ( BlockLink_t * ) xAlignedHeap;
			xStart.xBlockSize = ( size_t ) 0;
		}
		else
		{
			/* Should only get here if one region has already been added to the
			heap. */
			configASSERT( pxEnd != NULL );
			/* Check blocks are passed in with increasing start addresses. */
			configASSERT( xAddress > ( size_t ) pxEnd );
		}
		/* Remember the location of the end marker in the previous region, if
		any. */
		pxPreviousFreeBlock = pxEnd;
		/* pxEnd is used to mark the end of the list of free blocks and is
		inserted at the end of the region space. */
		xAddress = xAlignedHeap + xTotalRegionSize;
		xAddress -= xHeapStructSize;
		xAddress &= ~portBYTE_ALIGNMENT_MASK;
		pxEnd = ( BlockLink_t * ) xAddress;
		pxEnd->xBlockSize = 0;
		pxEnd->pxNextFreeBlock = NULL;
		/* To start with there is a single free block in this region that is
		sized to take up the entire heap region minus the space taken by the
		free block structure. */
		pxFirstFreeBlockInRegion = ( BlockLink_t * ) xAlignedHeap;
		pxFirstFreeBlockInRegion->xBlockSize = xAddress - ( size_t ) pxFirstFreeBlockInRegion;
		pxFirstFreeBlockInRegion->pxNextFreeBlock = pxEnd;
		/* If this is not the first region that makes up the entire heap space
		then link the previous region to this region. */
		if( pxPreviousFreeBlock != NULL )
		{
			pxPreviousFreeBlock->pxNextFreeBlock = pxFirstFreeBlockInRegion;
		}
		xTotalHeapSize += pxFirstFreeBlockInRegion->xBlockSize;
		/* Move onto the next HeapRegion_t structure. */
		//下一块
		xDefinedRegions++;
		pxHeapRegion = &( pxHeapRegions[ xDefinedRegions ] );
	}
	xMinimumEverFreeBytesRemaining = xTotalHeapSize;
	xFreeBytesRemaining = xTotalHeapSize;
	/* Check something was actually defined before it is accessed. */
	configASSERT( xTotalHeapSize );
	/* Work out the position of the top bit in a size_t variable. */
	xBlockAllocatedBit = ( ( size_t ) 1 ) << ( ( sizeof( size_t ) * heapBITS_PER_BYTE ) - 1 );
}

常见问题

比如有多块内存，一块是内部ram，其他是外部ram，外部的地址能写死确定，但是内部的会随着程序开发不停改变，怎么确定呢，下面是官网给的例子

/* Define the start address and size of the two RAM regions not used by the 
linker. */
#define RAM2_START_ADDRESS ( ( uint8_t * ) 0x00020000 )
#define RAM2_SIZE ( 32 * 1024 )
#define RAM3_START_ADDRESS ( ( uint8_t * ) 0x00030000 )
#define RAM3_SIZE ( 32 * 1024 )
/* Declare an array that will be part of the heap used by heap_5. The array will be 
placed in RAM1 by the linker. */
#define RAM1_HEAP_SIZE ( 30 * 1024 )
static uint8_t ucHeap[ RAM1_HEAP_SIZE ];
/* Create an array of HeapRegion_t definitions. Whereas in Listing 6 the first entry 
described all of RAM1, so heap_5 will have used all of RAM1, this time the first 
entry only describes the ucHeap array, so heap_5 will only use the part of RAM1 that 
contains the ucHeap array. The HeapRegion_t structures must still appear in start 
address order, with the structure that contains the lowest start address appearing 
first. */
const HeapRegion_t xHeapRegions[] =
{
    { ucHeap, RAM1_HEAP_SIZE },
    { RAM2_START_ADDRESS, RAM2_SIZE },
    { RAM3_START_ADDRESS, RAM3_SIZE },
    { NULL, 0 } /* Marks the end of the array. */
};

这样就不用老是修改第一块的起始地址。

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