heap_2.c

FreeRTOS is a portable, open source, mini Real Time Kernel - a free to download and royalty free RTO

/*
	FreeRTOS.org V5.2.0 - Copyright (C) 2003-2009 Richard Barry.

	This file is part of the FreeRTOS.org distribution.

	FreeRTOS.org is free software; you can redistribute it and/or modify it 
	under the terms of the GNU General Public License (version 2) as published
	by the Free Software Foundation and modified by the FreeRTOS exception.

	FreeRTOS.org is distributed in the hope that it will be useful,	but WITHOUT
	ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
	FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for 
	more details.

	You should have received a copy of the GNU General Public License along 
	with FreeRTOS.org; if not, write to the Free Software Foundation, Inc., 59 
	Temple Place, Suite 330, Boston, MA  02111-1307  USA.

	A special exception to the GPL is included to allow you to distribute a 
	combined work that includes FreeRTOS.org without being obliged to provide
	the source code for any proprietary components.  See the licensing section
	of http://www.FreeRTOS.org for full details.


	***************************************************************************
	*                                                                         *
	* Get the FreeRTOS eBook!  See http://www.FreeRTOS.org/Documentation      *
	*                                                                         *
	* This is a concise, step by step, 'hands on' guide that describes both   *
	* general multitasking concepts and FreeRTOS specifics. It presents and   *
	* explains numerous examples that are written using the FreeRTOS API.     *
	* Full source code for all the examples is provided in an accompanying    *
	* .zip file.                                                              *
	*                                                                         *
	***************************************************************************

	1 tab == 4 spaces!

	Please ensure to read the configuration and relevant port sections of the
	online documentation.

	http://www.FreeRTOS.org - Documentation, latest information, license and
	contact details.

	http://www.SafeRTOS.com - A version that is certified for use in safety
	critical systems.

	http://www.OpenRTOS.com - Commercial support, development, porting,
	licensing and training services.
*/

/*
 * 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.
 *
 * See heap_1.c and heap_3.c for alternative implementations, and the memory
 * management pages of http://www.FreeRTOS.org for more information.
 */
#include <stdlib.h>

#include "FreeRTOS.h"
#include "task.h"

/* Setup the correct byte alignment mask for the defined byte alignment. */

#if portBYTE_ALIGNMENT == 8
	#define heapBYTE_ALIGNMENT_MASK ( ( size_t ) 0x0007 )
#endif

#if portBYTE_ALIGNMENT == 4
	#define heapBYTE_ALIGNMENT_MASK	( ( size_t ) 0x0003 )
#endif

#if portBYTE_ALIGNMENT == 2
	#define heapBYTE_ALIGNMENT_MASK	( ( size_t ) 0x0001 )
#endif

#if portBYTE_ALIGNMENT == 1
	#define heapBYTE_ALIGNMENT_MASK	( ( size_t ) 0x0000 )
#endif

#ifndef heapBYTE_ALIGNMENT_MASK
	#error "Invalid portBYTE_ALIGNMENT definition"
#endif

/* Allocate the memory for the heap.  The struct is used to force byte
alignment without using any non-portable code. */
static struct xRTOS_HEAP
{
	unsigned portLONG ulDummy;
	unsigned portCHAR ucHeap[ configTOTAL_HEAP_SIZE ];
} xHeap;

/* 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 portSHORT  heapSTRUCT_SIZE	= ( sizeof( xBlockLink ) + ( sizeof( xBlockLink ) % portBYTE_ALIGNMENT ) );
#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;

/* 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;									\
}
/*-----------------------------------------------------------*/

#define prvHeapInit()																\
{																					\
xBlockLink *pxFirstFreeBlock;														\
																					\
	/* 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 * ) xHeap.ucHeap;								\
	xStart.xBlockSize = ( size_t ) 0;												\
																					\
	/* xEnd is used to mark the end of the list of free blocks. */					\
	xEnd.xBlockSize = configTOTAL_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 * ) xHeap.ucHeap;										\
	pxFirstFreeBlock->xBlockSize = configTOTAL_HEAP_SIZE;							\
	pxFirstFreeBlock->pxNextFreeBlock = &xEnd;										\
}
/*-----------------------------------------------------------*/

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 & heapBYTE_ALIGNMENT_MASK )
			{
				/* Byte alignment required. */
				xWantedSize += ( portBYTE_ALIGNMENT - ( xWantedSize & heapBYTE_ALIGNMENT_MASK ) );
			}
		}

		if( ( xWantedSize > 0 ) && ( xWantedSize < configTOTAL_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 ) )
			{
				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 portCHAR * ) pxPreviousBlock->pxNextFreeBlock ) + heapSTRUCT_SIZE );

				/* This block is being returned for use so must be taken our 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 portCHAR * ) 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 ) );
				}
			}
		}
	}
	xTaskResumeAll();

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

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

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

		/* This casting is to keep the compiler from issuing warnings. */
		pxLink = ( void * ) puc;

		vTaskSuspendAll();
		{				
			/* Add this block to the list of free blocks. */
			prvInsertBlockIntoFreeList( ( ( xBlockLink * ) pxLink ) );
		}
		xTaskResumeAll();
	}
}
/*-----------------------------------------------------------*/