heap_2.c

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*/

/*
 * A sample implementation of pvPortMalloc() and vPortFree() that permits
 * allocated blocks to be freed, but does not combine adjacent free blocks
 * into a single larger block (and so will fragment memory).  See heap_4.c for
 * an equivalent that does combine adjacent blocks into single larger blocks.
 *
 * See heap_1.c, heap_3.c and heap_4.c for alternative implementations, and the
 * memory management pages of http://www.FreeRTOS.org for more information.
 */
#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

/* A few bytes might be lost to byte aligning the heap start address. */
#define configADJUSTED_HEAP_SIZE    ( configTOTAL_HEAP_SIZE - portBYTE_ALIGNMENT )

/* 
 * Initialises the heap structures before their first use.
 */
static void prvHeapInit( void );

/* Allocate the memory for the heap. */
static unsigned char ucHeap[ configTOTAL_HEAP_SIZE ];

/* Define the linked list structure.  This is used to link free blocks in order
of their size. */
typedef struct A_BLOCK_LINK
{
    struct A_BLOCK_LINK *pxNextFreeBlock;   /*<< The next free block in the list. */
    size_t xBlockSize;                      /*<< The size of the free block. */
} xBlockLink;


static const unsigned short heapSTRUCT_SIZE = ( ( sizeof ( xBlockLink ) + ( portBYTE_ALIGNMENT - 1 ) ) & ~portBYTE_ALIGNMENT_MASK );
#define heapMINIMUM_BLOCK_SIZE  ( ( size_t ) ( heapSTRUCT_SIZE * 2 ) )

/* Create a couple of list links to mark the start and end of the list. */
static xBlockLink xStart, xEnd;

/* Keeps track of the number of free bytes remaining, but says nothing about
fragmentation. */
static size_t xFreeBytesRemaining = configADJUSTED_HEAP_SIZE;

/* STATIC FUNCTIONS ARE DEFINED AS MACROS TO MINIMIZE THE FUNCTION CALL DEPTH. */

/*
 * Insert a block into the list of free blocks - which is ordered by size of
 * the block.  Small blocks at the start of the list and large blocks at the end
 * of the list.
 */
#define prvInsertBlockIntoFreeList( pxBlockToInsert )                               \
{                                                                                   \
xBlockLink *pxIterator;                                                             \
size_t xBlockSize;                                                                  \
                                                                                    \
    xBlockSize = pxBlockToInsert->xBlockSize;                                       \
                                                                                    \
    /* Iterate through the list until a block is found that has a larger size */    \
    /* than the block we are inserting. */                                          \
    for( pxIterator = &xStart; pxIterator->pxNextFreeBlock->xBlockSize < xBlockSize; pxIterator = pxIterator->pxNextFreeBlock ) \
    {                                                                               \
        /* There is nothing to do here - just iterate to the correct position. */   \
    }                                                                               \
                                                                                    \
    /* Update the list to include the block being inserted in the correct */        \
    /* position. */                                                                 \
    pxBlockToInsert->pxNextFreeBlock = pxIterator->pxNextFreeBlock;                 \
    pxIterator->pxNextFreeBlock = pxBlockToInsert;                                  \
}
/*-----------------------------------------------------------*/

void *pvPortMalloc( size_t xWantedSize )
{
xBlockLink *pxBlock, *pxPreviousBlock, *pxNewBlockLink;
static portBASE_TYPE xHeapHasBeenInitialised = pdFALSE;
void *pvReturn = NULL;

    vTaskSuspendAll();
    {
        /* If this is the first call to malloc then the heap will require
        initialisation to setup the list of free blocks. */
        if( xHeapHasBeenInitialised == pdFALSE )
        {
            prvHeapInit();
            xHeapHasBeenInitialised = pdTRUE;
        }

        /* The wanted size is increased so it can contain a xBlockLink
        structure in addition to the requested amount of bytes. */
        if( xWantedSize > 0 )
        {
            xWantedSize += heapSTRUCT_SIZE;

            /* Ensure that blocks are always aligned to the required number of bytes. */
            if( ( xWantedSize & portBYTE_ALIGNMENT_MASK ) != 0 )
            {
                /* Byte alignment required. */
                xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & portBYTE_ALIGNMENT_MASK ) );
            }
        }

        if( ( xWantedSize > 0 ) && ( xWantedSize < configADJUSTED_HEAP_SIZE ) )
        {
            /* Blocks are stored in byte order - traverse the list from the start
            (smallest) 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 we found the end marker then a block of adequate size was not found. */
            if( pxBlock != &xEnd )
            {
                /* Return the memory space - jumping over the xBlockLink structure
                at its start. */
                pvReturn = ( void * ) ( ( ( unsigned char * ) pxPreviousBlock->pxNextFreeBlock ) + heapSTRUCT_SIZE );

                /* 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. */
                    pxNewBlockLink = ( void * ) ( ( ( unsigned char * ) pxBlock ) + xWantedSize );

                    /* 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 ) );
                }

                xFreeBytesRemaining -= pxBlock->xBlockSize;
            }
        }
        
        traceMALLOC( pvReturn, xWantedSize );
    }
    xTaskResumeAll();

    #if( configUSE_MALLOC_FAILED_HOOK == 1 )
    {
        if( pvReturn == NULL )
        {
            extern void vApplicationMallocFailedHook( void );
            vApplicationMallocFailedHook();
        }
    }
    #endif

    return pvReturn;
}
/*-----------------------------------------------------------*/

void vPortFree( void *pv )
{
unsigned char *puc = ( unsigned char * ) pv;
xBlockLink *pxLink;

    if( pv != NULL )
    {
        /* The memory being freed will have an xBlockLink structure immediately
        before it. */
        puc -= heapSTRUCT_SIZE;

        /* This unexpected casting is to keep some compilers from issuing 
        byte alignment warnings. */
        pxLink = ( void * ) puc;

        vTaskSuspendAll();
        {
            /* Add this block to the list of free blocks. */
            prvInsertBlockIntoFreeList( ( ( xBlockLink * ) pxLink ) );
            xFreeBytesRemaining += pxLink->xBlockSize;
            traceFREE( pv, pxLink->xBlockSize );
        }
        xTaskResumeAll();
    }
}
/*-----------------------------------------------------------*/

size_t xPortGetFreeHeapSize( void )
{
    return xFreeBytesRemaining;
}
/*-----------------------------------------------------------*/

void vPortInitialiseBlocks( void )
{
    /* This just exists to keep the linker quiet. */
}
/*-----------------------------------------------------------*/

static void prvHeapInit( void )
{
xBlockLink *pxFirstFreeBlock;
unsigned char *pucAlignedHeap;

    /* Ensure the heap starts on a correctly aligned boundary. */
    pucAlignedHeap = ( unsigned char * ) ( ( ( portPOINTER_SIZE_TYPE ) &ucHeap[ portBYTE_ALIGNMENT ] ) & ( ( portPOINTER_SIZE_TYPE ) ~portBYTE_ALIGNMENT_MASK ) );

    /* 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 = ( void * ) pucAlignedHeap;
    xStart.xBlockSize = ( size_t ) 0;

    /* xEnd is used to mark the end of the list of free blocks. */
    xEnd.xBlockSize = configADJUSTED_HEAP_SIZE;
    xEnd.pxNextFreeBlock = NULL;

    /* To start with there is a single free block that is sized to take up the
    entire heap space. */
    pxFirstFreeBlock = ( void * ) pucAlignedHeap;
    pxFirstFreeBlock->xBlockSize = configADJUSTED_HEAP_SIZE;
    pxFirstFreeBlock->pxNextFreeBlock = &xEnd;
}
/*-----------------------------------------------------------*/