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/*

 *  Heap Handler

 *

 *  COPYRIGHT (c) 1989-1999.

 *  On-Line Applications Research Corporation (OAR).

 *

 *  The license and distribution terms for this file may be

 *  found in the file LICENSE in this distribution or at

 *  http://www.OARcorp.com/rtems/license.html.

 *

 *  $Id: heap.c,v 1.2 2001-09-27 11:59:34 chris Exp $

 */

#include <rtems/system.h>

#include <rtems/score/sysstate.h>

#include <rtems/score/heap.h>

/*PAGE

 *

 *  _Heap_Initialize

 *

 *  This kernel routine initializes a heap.

 *

 *  Input parameters:

 *    the_heap         - pointer to heap header

 *    starting_address - starting address of heap

 *    size             - size of heap

 *    page_size        - allocatable unit of memory

 *

 *  Output parameters:

 *    returns - maximum memory available if RTEMS_SUCCESSFUL

 *    0       - otherwise

 *

 *    This is what a heap looks like in memory immediately

 *    after initialization:

 *

 *            +--------------------------------+

 *     0      |  size = 0      | status = used |  a.k.a.  dummy back flag

 *            +--------------------------------+

 *     4      |  size = size-8 | status = free |  a.k.a.  front flag

 *            +--------------------------------+

 *     8      |  next     = PERM HEAP_TAIL     |

 *            +--------------------------------+

 *    12      |  previous = PERM HEAP_HEAD     |

 *            +--------------------------------+

 *            |                                |

 *            |      memory available          |

 *            |       for allocation           |

 *            |                                |

 *            +--------------------------------+

 *  size - 8  |  size = size-8 | status = free |  a.k.a.  back flag

 *            +--------------------------------+

 *  size - 4  |  size = 0      | status = used |  a.k.a.  dummy front flag

 *            +--------------------------------+

 */

unsigned32 _Heap_Initialize(

  Heap_Control        *the_heap,

  void                *starting_address,

  unsigned32           size,

  unsigned32           page_size

)

{

  Heap_Block        *the_block;

  unsigned32         the_size;

  if ( !_Heap_Is_page_size_valid( page_size ) ||

       (size < HEAP_MINIMUM_SIZE) )

    return 0;

  the_heap->page_size = page_size;

  the_size = size - HEAP_OVERHEAD;

  the_block             = (Heap_Block *) starting_address;

  the_block->back_flag  = HEAP_DUMMY_FLAG;

  the_block->front_flag = the_size;

  the_block->next       = _Heap_Tail( the_heap );

  the_block->previous   = _Heap_Head( the_heap );

  the_heap->start          = the_block;

  the_heap->first          = the_block;

  the_heap->permanent_null = NULL;

  the_heap->last           = the_block;

  the_block             = _Heap_Next_block( the_block );

  the_block->back_flag  = the_size;

  the_block->front_flag = HEAP_DUMMY_FLAG;

  the_heap->final       = the_block;

  return ( the_size - HEAP_BLOCK_USED_OVERHEAD );

}