Add heap_4.c.

Source/portable/MemMang/heap_1.c

@@ -69,8 +69,8 @@
  * The simplest possible implementation of pvPortMalloc().  Note that this
  * implementation does NOT allow allocated memory to be freed again.
  *
- * See heap_2.c and heap_3.c for alternative implementations, and the memory
- * management pages of http://www.FreeRTOS.org for more information.
+ * See 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.
  */
 #include <stdlib.h>
 
@@ -142,8 +142,8 @@ void *pvReturn = NULL;
 
 void vPortFree( void *pv )
 {
-	/* Memory cannot be freed using this scheme.  See heap_2.c and heap_3.c 
-	for alternative implementations, and the memory management pages of 
+	/* Memory cannot be freed using this scheme.  See 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. */
 	( void ) pv;
 }

Source/portable/MemMang/heap_2.c

@@ -67,10 +67,11 @@
 /*
  * 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.
+ * into a single larger block (and so will fragment memory).  See heap_4.c for 
+ * an aquivalent that does combine adjacent blocks into single larger blocks.
  *
- * See heap_1.c and heap_3.c for alternative implementations, and the memory
- * management pages of http://www.FreeRTOS.org for more information.
+ * 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>
 
@@ -200,7 +201,7 @@ void *pvReturn = NULL;
 			(smallest) block until one of adequate size is found. */
 			pxPreviousBlock = &xStart;
 			pxBlock = xStart.pxNextFreeBlock;
-			while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock ) )
+			while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) )
 			{
 				pxPreviousBlock = pxBlock;
 				pxBlock = pxBlock->pxNextFreeBlock;
@@ -213,7 +214,7 @@ void *pvReturn = NULL;
 				at its start. */
 				pvReturn = ( void * ) ( ( ( unsigned char * ) pxPreviousBlock->pxNextFreeBlock ) + heapSTRUCT_SIZE );
 
-				/* This block is being returned for use so must be taken our of the
+				/* This block is being returned for use so must be taken out of the
 				list of free blocks. */
 				pxPreviousBlock->pxNextFreeBlock = pxBlock->pxNextFreeBlock;
 
@@ -259,7 +260,7 @@ void vPortFree( void *pv )
 unsigned char *puc = ( unsigned char * ) pv;
 xBlockLink *pxLink;
 
-	if( pv )
+	if( pv != NULL )
 	{
 		/* The memory being freed will have an xBlockLink structure immediately
 		before it. */

Source/portable/MemMang/heap_3.c

@@ -72,8 +72,8 @@
  * This file can only be used if the linker is configured to to generate
  * a heap memory area.
  *
- * See heap_2.c and heap_1.c for alternative implementations, and the memory
- * management pages of http://www.FreeRTOS.org for more information.
+ * See heap_1.c, heap_2.c and heap_4.c for alternative implementations, and the 
+ * memory management pages of http://www.FreeRTOS.org for more information.
  */
 
 #include <stdlib.h>