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FreeRTOS中对于内存的管理当前一共有5种实现方式（作者当前的版本是10.1.1），均在【 \Source\portable\MemMang 】下面，这里笔记下。
heap_5.c和heap_4.c实现方法比较相似。在调用API之前需要想调用 vPortDefineHeapRegions()来初始化内存堆。
heap5 允许内存堆跨越多个连续的内存段。比如STM32内部RAM做内存堆，但是需要大内存时候，可外接SRAM甚至SDRAM。
首先定义内存段：
HeapRegion_t xHeapRegions[]=
{
{(uint8_t *)0x200001C0UL,0x10000}, //内部 RAM，内存起始地址 0x200001C0 大小64KB
{(uint8_t *)0x68000000UL,0x100000},//外部SRAM，内存起始地址 0x68000000 大小1MB
{NULL,0} //数组结尾
};在一开始就要调用函数vPortDefineHeapRegions完成内存堆的初始化！然后才能创建任务和堆栈。。。
heap5和heap4内容基本一样，请参照。
/*
heap5.c和heap4.c类似，但是heap5.c的内存是由外部定义的，因此在使用前必须调用函数vPortDefineHeapRegions()来说明要使用的内存。
vPortDefineHeapRegions()的入参可以参考下面的英文注释。
*/
/*
* A sample implementation of pvPortMalloc() that allows the heap to be defined
* across multiple non-contigous blocks and combines (coalescences) adjacent
* memory blocks as they are freed.
*
* See heap_1.c, heap_2.c, heap_3.c and heap_4.c for alternative
* implementations, and the memory management pages of http://www.FreeRTOS.org
* for more information.
*
* Usage notes:
*
* vPortDefineHeapRegions() ***must*** be called before pvPortMalloc().
* pvPortMalloc() will be called if any task objects (tasks, queues, event
* groups, etc.) are created, therefore vPortDefineHeapRegions() ***must*** be
* called before any other objects are defined.
*
* 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
* {
* uint8_t *pucStartAddress; << Start address of a block of memory that will be part of the heap.
* size_t xSizeInBytes; << Size of the block of memory.
* } HeapRegion_t;
*
* The array is terminated using a NULL zero sized region definition, and the
* memory regions defined in the array ***must*** appear in address order from
* low address to high address. So the following is a valid example of how
* to use the function.
*
* HeapRegion_t xHeapRegions[] =
* {
* { ( uint8_t * ) 0x80000000UL, 0x10000 }, << Defines a block of 0x10000 bytes starting at address 0x80000000
* { ( uint8_t * ) 0x90000000UL, 0xa0000 }, << Defines a block of 0xa0000 bytes starting at address of 0x90000000
* { NULL, 0 } << Terminates the array.
* };
*
* vPortDefineHeapRegions( xHeapRegions ); << Pass the array into vPortDefineHeapRegions().
*
* Note 0x80000000 is the lower address so appears in the array first.
*
*/
#include <stdlib.h>
/* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining
all the API functions to use the MPU wrappers. That should only be done when
task.h is included from an application file. */
#define MPU_WRAPPERS_INCLUDED_FROM_API_FILE
#include "FreeRTOS.h"
#include "task.h"
#undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE
/* Block sizes must not get too small. */
#define heapMINIMUM_BLOCK_SIZE ( ( size_t ) ( uxHeapStructSize << 1 ) )
/*
1个byte有8个bits
*/
/* Assumes 8bit bytes! */
#define heapBITS_PER_BYTE ( ( size_t ) 8 )
/* Define the linked list structure. This is used to link free blocks in order
of their memory address. */
typedef struct A_BLOCK_LINK
{
struct A_BLOCK_LINK *pxNextFreeBlock; /*<< The next free block in the list. */
/* 链表形式存储，保存指向下一块空闲内存的结构体，注意这里是单向链表 */
size_t xBlockSize; /*<< The size of the free block. */
/* 该块空闲内存的大小，注意这里BlockLink_t其实也是放在它对应的空余内存的头部的，但是空闲内存的大小并没有考虑放入的BlockLink_t */
} BlockLink_t;
//空闲内存管理结构体，通过它来管理释放回来的内存
/*-----------------------------------------------------------*/
/*
* Inserts a block of memory that is being freed into the correct position in
* the list of free memory blocks. The block being freed will be merged with
* the block in front it and/or the block behind it if the memory blocks are
* adjacent to each other.
*/
static void prvInsertBlockIntoFreeList( BlockLink_t *pxBlockToInsert );
/*-----------------------------------------------------------*/
/* The size of the structure placed at the beginning of each allocated memory
block must by correctly byte aligned. */
/* 考虑到字节对齐后BlockLink_t的大小 */
static const uint32_t uxHeapStructSize = ( ( sizeof ( BlockLink_t ) + ( portBYTE_ALIGNMENT - 1 ) ) & ~portBYTE_ALIGNMENT_MASK );
/* 单向链表，注意这里的链表不是以内存大小为依据排序的，而是以内存位置为依据排序的，这样是为了方便空闲内存的合并 */
/* Create a couple of list links to mark the start and end of the list. */
static BlockLink_t xStart, *pxEnd = NULL;
/* Keeps track of the number of free bytes remaining, but says nothing about
fragmentation. */
static size_t xFreeBytesRemaining = 0;
static size_t xMinimumEverFreeBytesRemaining = 0;
/* Gets set to the top bit of an size_t type. When this bit in the xBlockSize
member of an BlockLink_t structure is set then the block belongs to the
application. When the bit is free the block is still part of the free heap
space. */
static size_t xBlockAllocatedBit = 0;
/*-----------------------------------------------------------*/
void *pvPortMalloc( size_t xWantedSize )
{
BlockLink_t *pxBlock, *pxPreviousBlock, *pxNewBlockLink;
void *pvReturn = NULL;
/* 使用heap5时，必须显式的初始化，这里通过pxEnd来判断是否已经显式的初始化 */
/* The heap must be initialised before the first call to
prvPortMalloc(). */
configASSERT( pxEnd );
vTaskSuspendAll();//首先暂停当前所有执行的任务
{
/* Check the requested block size is not so large that the top bit is
set. The top bit of the block size member of the BlockLink_t structure
is used to determine who owns the block - the application or the
kernel, so it must be free. */
/*这里xWantedSize的大小有要求，需要最高位为0。因为后面BlockLink_t结构体中的xBlockSize的最高位需要使用。*/
if( ( xWantedSize & xBlockAllocatedBit ) == 0 )
{
/* The wanted size is increased so it can contain a BlockLink_t
structure in addition to the requested amount of bytes. */
if( xWantedSize > 0 )
{
xWantedSize += uxHeapStructSize;
/* 空余内存的头部要放一个BlockLink_t来管理，因此这里需要人为的扩充下申请的内存大小 */
/* Ensure that blocks are always aligned to the required number
of bytes. */
if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0x00 )
{/* 保证字节对齐 */
/* Byte alignment required. */
xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* 人为扩充后的大小小于空闲内存，可以存放 */
if( ( xWantedSize > 0 ) && ( xWantedSize <= xFreeBytesRemaining ) )
{ //从空余内存链表的头部开始找，如果该空余内存的大小>xWantedSize，就标记该内存为pxBlock
/* Traverse the list from the start (lowest address) block until
one of adequate size is found. */
pxPreviousBlock = &xStart;
pxBlock = xStart.pxNextFreeBlock;
while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) )
{
pxPreviousBlock = pxBlock;
pxBlock = pxBlock->pxNextFreeBlock;
}
/* If the end marker was reached then a block of adequate size
was not found. */
/* 如果pxBlock不是pxEnd,说明上面的while已经找到了合适的内存 */
if( pxBlock != pxEnd )
{
/* Return the memory space pointed to - jumping over the
BlockLink_t structure at its start. */
pvReturn = ( void * ) ( ( ( uint8_t * ) pxPreviousBlock->pxNextFreeBlock ) + uxHeapStructSize );
/* This block is being returned for use so must be taken out
of the list of free blocks. */
pxPreviousBlock->pxNextFreeBlock = pxBlock->pxNextFreeBlock;
/* If the block is larger than required it can be split into
two. */
if( ( pxBlock->xBlockSize - xWantedSize ) > heapMINIMUM_BLOCK_SIZE )
{
/* This block is to be split into two. Create a new
block following the number of bytes requested. The void
cast is used to prevent byte alignment warnings from the
compiler. */
/* 找到了，就把该块内存返回给用户，注意内存的头部有BlockLink_t，需要偏移掉 */
pxNewBlockLink = ( void * ) ( ( ( uint8_t * ) pxBlock ) + xWantedSize );
//将剩下的内存构造成一个新的pxNewBlockLink，加入到空闲链表中
/* Calculate the sizes of two blocks split from the
single block. */
pxNewBlockLink->xBlockSize = pxBlock->xBlockSize - xWantedSize;
pxBlock->xBlockSize = xWantedSize;
/* Insert the new block into the list of free blocks. */
prvInsertBlockIntoFreeList( ( pxNewBlockLink ) );
}
else
{
mtCOVERAGE_TEST_MARKER();
}
//更新剩余内存总大小
xFreeBytesRemaining -= pxBlock->xBlockSize;
//更新最小内存统计值
if( xFreeBytesRemaining < xMinimumEverFreeBytesRemaining )
{
xMinimumEverFreeBytesRemaining = xFreeBytesRemaining;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
//注意这里的xBlockSize的最高位被设置为1，标记了该内存是pvPortMalloc返回的。
/* The block is being returned - it is allocated and owned
by the application and has no "next" block. */
pxBlock->xBlockSize |= xBlockAllocatedBit;
pxBlock->pxNextFreeBlock = NULL;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
traceMALLOC( pvReturn, xWantedSize );
}
( void ) xTaskResumeAll();//恢复执行
//如果定义了钩子函数，那么申请失败时就调用钩子函数
#if( configUSE_MALLOC_FAILED_HOOK == 1 )
{
if( pvReturn == NULL )
{
extern void vApplicationMallocFailedHook( void );
vApplicationMallocFailedHook();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
#endif
return pvReturn;
}
/*-----------------------------------------------------------*/
void vPortFree( void *pv )
{
uint8_t *puc = ( uint8_t * ) pv;
BlockLink_t *pxLink;
if( pv != NULL )
{
/* The memory being freed will have an BlockLink_t structure immediately
before it. */
puc -= uxHeapStructSize;//这里向前偏移，重新找回BlockLink_t
/* This casting is to keep the compiler from issuing warnings. */
pxLink = ( void * ) puc;
/* Check the block is actually allocated. */
configASSERT( ( pxLink->xBlockSize & xBlockAllocatedBit ) != 0 );
configASSERT( pxLink->pxNextFreeBlock == NULL );
/* 如果xBlockSize的最高位为1，说明该块内存是pvPortMalloc申请的，那么通过pxBlock->xBlockSize |= xBlockAllocatedBit;
可以知道该块内存的真实大小为pxLink->xBlockSize &= ~xBlockAllocatedBit，即最高位改回0后的值。
*/
if( ( pxLink->xBlockSize & xBlockAllocatedBit ) != 0 )
{
if( pxLink->pxNextFreeBlock == NULL )
{
/* The block is being returned to the heap - it is no longer
allocated. */
pxLink->xBlockSize &= ~xBlockAllocatedBit;
vTaskSuspendAll();
{
/* Add this block to the list of free blocks. */
//更新剩余内存总大小
xFreeBytesRemaining += pxLink->xBlockSize;
traceFREE( pv, pxLink->xBlockSize );
//将这块内存放到空闲链表中
prvInsertBlockIntoFreeList( ( ( BlockLink_t * ) pxLink ) );
}
( void ) xTaskResumeAll();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else//如果xBlockSize的最高位不为1，那么说明该块内存不是通过pvPortMalloc申请的，那么直接忽略处理
{
mtCOVERAGE_TEST_MARKER();
}
}
}
/*-----------------------------------------------------------*/
size_t xPortGetFreeHeapSize( void )
{
return xFreeBytesRemaining;
}
/*-----------------------------------------------------------*/
size_t xPortGetMinimumEverFreeHeapSize( void )
{
return xMinimumEverFreeBytesRemaining;
}
/*-----------------------------------------------------------*/
/*
将一个BlockLink_t的指针插入到单向链表中，注意这里会合并空闲内存
*/
static void prvInsertBlockIntoFreeList( BlockLink_t *pxBlockToInsert )
{
BlockLink_t *pxIterator;
uint8_t *puc;
/* 首先找到和pxBlockToInsert【前面】相邻的空闲内存 */
/* Iterate through the list until a block is found that has a higher address
than the block being inserted. */
for( pxIterator = &xStart; pxIterator->pxNextFreeBlock < pxBlockToInsert; pxIterator = pxIterator->pxNextFreeBlock )
{
/* Nothing to do here, just iterate to the right position. */
}
/* Do the block being inserted, and the block it is being inserted after
make a contiguous block of memory? */
puc = ( uint8_t * ) pxIterator;
/* 循环结束后，如果找到的内存和pxBlockToInsert相邻，并且在pxBlockToInsert前面，那么就把pxBlockToInsert合并到该内存中 */
if( ( puc + pxIterator->xBlockSize ) == ( uint8_t * ) pxBlockToInsert )//如果一个内存的尾部恰好是pxBlockToInsert头部
{
pxIterator->xBlockSize += pxBlockToInsert->xBlockSize;//将pxBlockToInsert的大小合入该内存中
pxBlockToInsert = pxIterator;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
/* 判断pxBlockToInsert是否和后面的空闲内存相邻 */
/* Do the block being inserted, and the block it is being inserted before
make a contiguous block of memory? */
puc = ( uint8_t * ) pxBlockToInsert;
if( ( puc + pxBlockToInsert->xBlockSize ) == ( uint8_t * ) pxIterator->pxNextFreeBlock )
{
if( pxIterator->pxNextFreeBlock != pxEnd )
{/* 将后面的内存合入pxBlockToInsert，并用pxBlockToInsert代替该内存在链表中的位置 */
/* Form one big block from the two blocks. */
pxBlockToInsert->xBlockSize += pxIterator->pxNextFreeBlock->xBlockSize;
pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock->pxNextFreeBlock;
}
else
{
pxBlockToInsert->pxNextFreeBlock = pxEnd;
}
}
else
{
/* 后面不相邻，那么只能加入链表了 */
pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock;
}
/* If the block being inserted plugged a gab, so was merged with the block
before and the block after, then it's pxNextFreeBlock pointer will have
already been set, and should not be set here as that would make it point
to itself. */
/* 判断下前面是否已经合并了，如果合并了，就不用在更新链表了 */
if( pxIterator != pxBlockToInsert )
{
pxIterator->pxNextFreeBlock = pxBlockToInsert;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
/*-----------------------------------------------------------*/
void vPortDefineHeapRegions( const HeapRegion_t * const pxHeapRegions )
{
BlockLink_t *pxFirstFreeBlockInRegion = NULL, *pxPreviousFreeBlock;
uint8_t *pucAlignedHeap;
size_t xTotalRegionSize, xTotalHeapSize = 0;
BaseType_t xDefinedRegions = 0;
uint32_t ulAddress;
const HeapRegion_t *pxHeapRegion;
/* Can only call once! */
/* vPortDefineHeapRegions必须被显式的调用而且只能调用一次 */
configASSERT( pxEnd == NULL );
pxHeapRegion = &( pxHeapRegions[ xDefinedRegions ] );
while( pxHeapRegion->xSizeInBytes > 0 )
{
xTotalRegionSize = pxHeapRegion->xSizeInBytes;
/* 保证内存起始地址按照字节对齐 */
/* Ensure the heap region starts on a correctly aligned boundary. */
ulAddress = ( uint32_t ) pxHeapRegion->pucStartAddress;
if( ( ulAddress & portBYTE_ALIGNMENT_MASK ) != 0 )
{
ulAddress += ( portBYTE_ALIGNMENT - 1 );
ulAddress &= ~portBYTE_ALIGNMENT_MASK;
/* Adjust the size for the bytes lost to alignment. */
xTotalRegionSize -= ulAddress - ( uint32_t ) pxHeapRegion->pucStartAddress;
}
pucAlignedHeap = ( uint8_t * ) ulAddress;
/* 将修正后的内存构造成一个BlockLink_t，插入空闲单向链表中。 */
/* 这里需要注意，由于入参是一个内存数组，而且每块内存都不一定相邻，因此每一块内存都会被构造成一个BlockLink_t，并插入到空闲链表中。
由于入参保证了内存顺序是由小到大的，因此这里内存构造成的BlockLink_t可以直接链接成空闲链表，不用再次排序。
*/
/* 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 * ) pucAlignedHeap;
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( ulAddress > ( uint32_t ) pxEnd );
}
/* Remember the location of the end marker in the previous region, if
any. */
pxPreviousFreeBlock = pxEnd;
/*
每次循环，都会对pxEnd重新赋值，因此，当循环结束后，pxEnd会指向最后一个内存块的尾部。
*/
/* pxEnd is used to mark the end of the list of free blocks and is
inserted at the end of the region space. */
ulAddress = ( ( uint32_t ) pucAlignedHeap ) + xTotalRegionSize;
ulAddress -= uxHeapStructSize;
ulAddress &= ~portBYTE_ALIGNMENT_MASK;
pxEnd = ( BlockLink_t * ) ulAddress;
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 * ) pucAlignedHeap;
pxFirstFreeBlockInRegion->xBlockSize = ulAddress - ( uint32_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. */
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 );
}