FreeRTOS/Source/list.c

   1 /*
   2     FreeRTOS V6.0.5 - Copyright (C) 2010 Real Time Engineers Ltd.
   3
   4     ***************************************************************************
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  14     *                                                                         *
  15     *        "Using the FreeRTOS Real Time Kernel - a Practical Guide"        *
  16     *                  http://www.FreeRTOS.org/Documentation                  *
  17     *                                                                         *
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  24
  25     This file is part of the FreeRTOS distribution.
  26
  27     FreeRTOS is free software; you can redistribute it and/or modify it under
  28     the terms of the GNU General Public License (version 2) as published by the
  29     Free Software Foundation AND MODIFIED BY the FreeRTOS exception.
  30     ***NOTE*** The exception to the GPL is included to allow you to distribute
  31     a combined work that includes FreeRTOS without being obliged to provide the
  32     source code for proprietary components outside of the FreeRTOS kernel.
  33     FreeRTOS is distributed in the hope that it will be useful, but WITHOUT
  34     ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  35     FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  36     more details. You should have received a copy of the GNU General Public
  37     License and the FreeRTOS license exception along with FreeRTOS; if not it
  38     can be viewed here: http://www.freertos.org/a00114.html and also obtained
  39     by writing to Richard Barry, contact details for whom are available on the
  40     FreeRTOS WEB site.
  41
  42     1 tab == 4 spaces!
  43
  44     http://www.FreeRTOS.org - Documentation, latest information, license and
  45     contact details.
  46
  47     http://www.SafeRTOS.com - A version that is certified for use in safety
  48     critical systems.
  49
  50     http://www.OpenRTOS.com - Commercial support, development, porting,
  51     licensing and training services.
  52 */
  53
  54
  55 #include <stdlib.h>
  56 #include "FreeRTOS.h"
  57 #include "list.h"
  58
  59 /*-----------------------------------------------------------
  60  * PUBLIC LIST API documented in list.h
  61  *----------------------------------------------------------*/
  62
  63 void vListInitialise( xList *pxList )
  64 {
  65         /* The list structure contains a list item which is used to mark the
  66         end of the list.  To initialise the list the list end is inserted
  67         as the only list entry. */
  68         pxList->pxIndex = ( xListItem * ) &( pxList->xListEnd );
  69
  70         /* The list end value is the highest possible value in the list to
  71         ensure it remains at the end of the list. */
  72         pxList->xListEnd.xItemValue = portMAX_DELAY;
  73
  74         /* The list end next and previous pointers point to itself so we know
  75         when the list is empty. */
  76         pxList->xListEnd.pxNext = ( xListItem * ) &( pxList->xListEnd );
  77         pxList->xListEnd.pxPrevious = ( xListItem * ) &( pxList->xListEnd );
  78
  79         pxList->uxNumberOfItems = 0;
  80 }
  81 /*-----------------------------------------------------------*/
  82
  83 void vListInitialiseItem( xListItem *pxItem )
  84 {
  85         /* Make sure the list item is not recorded as being on a list. */
  86         pxItem->pvContainer = NULL;
  87 }
  88 /*-----------------------------------------------------------*/
  89
  90 void vListInsertEnd( xList *pxList, xListItem *pxNewListItem )
  91 {
  92 volatile xListItem * pxIndex;
  93
  94         /* Insert a new list item into pxList, but rather than sort the list,
  95         makes the new list item the last item to be removed by a call to
  96         pvListGetOwnerOfNextEntry.  This means it has to be the item pointed to by
  97         the pxIndex member. */
  98         pxIndex = pxList->pxIndex;
  99
 100         pxNewListItem->pxNext = pxIndex->pxNext;
 101         pxNewListItem->pxPrevious = pxList->pxIndex;
 102         pxIndex->pxNext->pxPrevious = ( volatile xListItem * ) pxNewListItem;
 103         pxIndex->pxNext = ( volatile xListItem * ) pxNewListItem;
 104         pxList->pxIndex = ( volatile xListItem * ) pxNewListItem;
 105
 106         /* Remember which list the item is in. */
 107         pxNewListItem->pvContainer = ( void * ) pxList;
 108
 109         ( pxList->uxNumberOfItems )++;
 110 }
 111 /*-----------------------------------------------------------*/
 112
 113 void vListInsert( xList *pxList, xListItem *pxNewListItem )
 114 {
 115 volatile xListItem *pxIterator;
 116 portTickType xValueOfInsertion;
 117
 118         /* Insert the new list item into the list, sorted in ulListItem order. */
 119         xValueOfInsertion = pxNewListItem->xItemValue;
 120
 121         /* If the list already contains a list item with the same item value then
 122         the new list item should be placed after it.  This ensures that TCB's which
 123         are stored in ready lists (all of which have the same ulListItem value)
 124         get an equal share of the CPU.  However, if the xItemValue is the same as
 125         the back marker the iteration loop below will not end.  This means we need
 126         to guard against this by checking the value first and modifying the
 127         algorithm slightly if necessary. */
 128         if( xValueOfInsertion == portMAX_DELAY )
 129         {
 130                 pxIterator = pxList->xListEnd.pxPrevious;
 131         }
 132         else
 133         {
 134                 /* *** NOTE ***********************************************************
 135                 If you find your application is crashing here then likely causes are:
 136                         1) Stack overflow -
 137                            see http://www.freertos.org/Stacks-and-stack-overflow-checking.html
 138                         2) Incorrect interrupt priority assignment, especially on Cortex M3
 139                            parts where numerically high priority values denote low actual
 140                            interrupt priories, which can seem counter intuitive.  See
 141                            configMAX_SYSCALL_INTERRUPT_PRIORITY on http://www.freertos.org/a00110.html
 142                         3) Calling an API function from within a critical section or when
 143                            the scheduler is suspended.
 144                         4) Using a queue or semaphore before it has been initialised or
 145                            before the scheduler has been started (are interrupts firing
 146                            before vTaskStartScheduler() has been called?).
 147                 See http://www.freertos.org/FAQHelp.html for more tips.
 148                 **********************************************************************/
 149
 150                 for( pxIterator = ( xListItem * ) &( pxList->xListEnd ); pxIterator->pxNext->xItemValue <= xValueOfInsertion; pxIterator = pxIterator->pxNext )
 151                 {
 152                         /* There is nothing to do here, we are just iterating to the
 153                         wanted insertion position. */
 154                 }
 155         }
 156
 157         pxNewListItem->pxNext = pxIterator->pxNext;
 158         pxNewListItem->pxNext->pxPrevious = ( volatile xListItem * ) pxNewListItem;
 159         pxNewListItem->pxPrevious = pxIterator;
 160         pxIterator->pxNext = ( volatile xListItem * ) pxNewListItem;
 161
 162         /* Remember which list the item is in.  This allows fast removal of the
 163         item later. */
 164         pxNewListItem->pvContainer = ( void * ) pxList;
 165
 166         ( pxList->uxNumberOfItems )++;
 167 }
 168 /*-----------------------------------------------------------*/
 169
 170 void vListRemove( xListItem *pxItemToRemove )
 171 {
 172 xList * pxList;
 173
 174         pxItemToRemove->pxNext->pxPrevious = pxItemToRemove->pxPrevious;
 175         pxItemToRemove->pxPrevious->pxNext = pxItemToRemove->pxNext;
 176
 177         /* The list item knows which list it is in.  Obtain the list from the list
 178         item. */
 179         pxList = ( xList * ) pxItemToRemove->pvContainer;
 180
 181         /* Make sure the index is left pointing to a valid item. */
 182         if( pxList->pxIndex == pxItemToRemove )
 183         {
 184                 pxList->pxIndex = pxItemToRemove->pxPrevious;
 185         }
 186
 187         pxItemToRemove->pvContainer = NULL;
 188         ( pxList->uxNumberOfItems )--;
 189 }
 190 /*-----------------------------------------------------------*/
 191