FreeRTOS --（6）内存管理 heap5

转载自https://blog.csdn.net/zhoutaopower/article/details/106748308

FreeRTOS 中的 heap 5 内存管理，相对于 heap 4《FreeRTOS --（5）内存管理 heap4》 只增加了对非连续内存区域的管理，什么叫非连续区域内存呢？比如一款芯片，它即支持了内部的 RAM，也支持了外挂 RAM，那么这两个内存就可能在地址上不是连续的，比如 RAM1、RAM2、RAM3，如下所示：

针对这种情况，就可以使用 heap 5 来管理；

不同于之前的 heap 管理，heap 5 引入了一个结构体来管理这些非连续的区域：

typedef struct HeapRegion
{
 /* The start address of a block of memory that will be part of the heap.*/
 uint8_t *pucStartAddress;
 /* The size of the block of memory in bytes. */
 size_t xSizeInBytes;
} HeapRegion_t;

一个块连续的内存用一个 HeapRegion_t 表示，多个连续内存通过 HeapRegion_t 数组的形式组织成为了所有的内存；

heap 5 要求，在调用正式的内存分配函数之前，需要定义 HeapRegion，并调用 vPortDefineHeapRegions 来初始化它；

官方给了一个 demo：

/* Define the start address and size of the three RAM regions. */
#define RAM1_START_ADDRESS ( ( uint8_t * ) 0x00010000 )
#define RAM1_SIZE ( 65 * 1024 )

#define RAM2_START_ADDRESS ( ( uint8_t * ) 0x00020000 )
#define RAM2_SIZE ( 32 * 1024 )

#define RAM3_START_ADDRESS ( ( uint8_t * ) 0x00030000 )
#define RAM3_SIZE ( 32 * 1024 )

/* Create an array of HeapRegion_t definitions, with an index for each of the three
RAM regions, and terminating the array with a NULL address. The HeapRegion_t
structures must appear in start address order, with the structure that contains the
lowest start address appearing first. */
const HeapRegion_t xHeapRegions[] =
{
    { RAM1_START_ADDRESS, RAM1_SIZE },
    { RAM2_START_ADDRESS, RAM2_SIZE },
    { RAM3_START_ADDRESS, RAM3_SIZE },
    { NULL, 0 } /* Marks the end of the array. */
};
int main( void ) {
    /* Initialize heap_5. */
    vPortDefineHeapRegions( xHeapRegions );
    /* Add application code here. */
}

如果有 3 个 RAM 区域的话，那么这样去定义他们；

需要注意的几点是：

1、定义 HeapRegion_t 数组的时候，最后一定要定义成为 NULL 和 0，这样接口才知道这是终点；

2、被定义的 RAM 区域，都会去参与内存管理；

那么问题就来了，在真实使用的时候，有可能你很难去定义部分 RAM 的 Start Address！

比如，一款芯片，它告诉你，它的第一块 RAM 有 64KB，第二块 RAM 有 32KB，第三块 RAM 有 32KB，那么你显然不能够直接将这些内存信息，按照上面 demo 代码的形式，定义到这个表格中，因为在编译阶段，有可能你相关的代码和数据等等（.text，.data，.bss，等）都会占用一部分的 RAM，但凡是定义到这个 HeapRegion_t 数组表格的，都会参与内存管理的行为，这显然是我们不愿意的；

也就是说，比如你芯片的 RAM 起始地址 0x2000_0000，你编译你的 Source Code 后，相关的代码和数据要占用 20KB，也就是 0x5000；那么你定义的 RAM1_START_ADDRESS 起始地址，就必须要大于 0x2000_0000+0x5000，这样才不会踩到你的其他数据；但是呢？你总不可能每次编译完都去改你的这个表吧？这是很痛苦的事情；

所有考虑到实际的使用，官方给出参考 demo 的方法是：

/* 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. */
};

即，将链接的代码数据，根据链接器(Linker)配置后，这些都放置在第一段的区域，ucHeap 也放在一样的地方，这样就避免去根据 map 文件去硬编码这个表格；

通过 beyond compare 可以知道，heap 5 和 heap 4 的代码在分配内存的 pvPortMalloc，和释放内存的 vPortFree，以及插入节点合并空闲内存 prvInsertBlockIntoFreeList 的部分，几乎完全一样，唯一不一样的地方在于：

heap 4 的内存初始化用的是 prvHeapInit

heap 5 的内存初始化用的是 vPortDefineHeapRegions

那我们就来看看这个 vPortDefineHeapRegions 的实现：

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. */
        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 );
}

经过一些对齐操作，将 demo 中的 3 块内存通过链表的方式挂接起来了，只不过内存地址不连续而已，但是对于连续的内存地址中，照样在释放的时候，可以进行合并操作；