mirror of https://github.com/rusefi/ChibiOS.git
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/*
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ChibiOS/RT - Copyright (C) 2006-2007 Giovanni Di Sirio.
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This file is part of ChibiOS/RT.
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ChibiOS/RT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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ChibiOS/RT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/**
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* @page article_manage_memory How to manage memory
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* ChibiOS/RT is a static kernel so you don't need to manage memory at all
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* if your application doesn't really require it. This doesn't mean that
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* the OS is unable to manage memory but just that memory management is an
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* optional part of the whole.<br>
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* The OS offers three distinct ways to manage memory, each one with its
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* weaknesses and strengths:
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* - Core Memory Manager. See @ref memcore.
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* - Heap Allocator. See @ref heaps.
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* - Memory Pools. See @ref pools.
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* .
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* The three mechanisms are able to coexist and are well integrated, as example
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* the heap allocator uses the core memory manager in order to get more
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* memory blocks, memory pools can optionally do the same thing.
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*
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* <h2>The three subsystems</h2>
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* This is a small comparison table regarding the three subsystems, C-runtime
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* and static objects are thrown there for comparison:<br><br>
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* <table style="text-align: center; width: 95%;"
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* align="center" border="1" cellpadding="2" cellspacing="0">
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* <tr>
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* <th style="width: 100px; background-color: rgb(192, 192, 192);">
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* <small>Subsystem</small>
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* </th>
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* <th style="width: 80px; background-color: rgb(192, 192, 192);">
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* <small>Free capable</small>
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* </th>
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* <th style="width: 80px; background-color: rgb(192, 192, 192);">
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* <small>Constant time</small>
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* </th>
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* <th style="width: 80px; background-color: rgb(192, 192, 192);">
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* <small>Safe</small>
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* </th>
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* <th style="width: 80px; background-color: rgb(192, 192, 192);">
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* <small>From IRQ</small>
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* </th>
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* <th style="background-color: rgb(192, 192, 192);">
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* <small>Notes</small>
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* </th>
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* </tr>
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* <tr>
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* <th style="background-color: rgb(224, 224, 224);">
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* <small>Static Objects</small>
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* </th>
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* <td><small>N/A</small></td>
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* <td><small>N/A</small></td>
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* <td><small>YES</small></td>
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* <td><small>YES</small></td>
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* <td style="text-align: left;">
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* Preferred solution for safety applications.
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* </td>
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* </tr>
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* <tr>
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* <th style="background-color: rgb(224, 224, 224);">
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* <small>Core Memory Manager</small>
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* </th>
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* <td><small>NO</small></td>
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* <td><small>YES</small></td>
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* <td><small>YES</small></td>
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* <td><small>YES</small></td>
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* <td style="text-align: left;">
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* Fast and safe but unable to free allocated memory.
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* </td>
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* </tr>
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* <tr>
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* <th style="background-color: rgb(224, 224, 224);">
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* <small>Heap Allocator</small>
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* </th>
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* <td><small>YES</small></td>
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* <td><small>NO</small></td>
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* <td><small>NO</small></td>
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* <td><small>NO</small></td>
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* <td style="text-align: left;">
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* Unsafe because fragmentation and not constant time, cannot be used
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* from IRQ handlers.
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* </td>
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* </tr>
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* <tr>
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* <th style="background-color: rgb(224, 224, 224);">
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* <small>Memory Pools</small>
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* </th>
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* <td><small>YES</small></td>
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* <td><small>YES</small></td>
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* <td><small>YES</small></td>
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* <td><small>YES</small></td>
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* <td style="text-align: left;">
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* Fast and safe but it can handle fixed size objects only, you may have
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* multiple memory pools however.
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* </td>
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* </tr>
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* <tr>
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* <th style="background-color: rgb(224, 224, 224);">
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* <small>C-Runtime</small>
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* </th>
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* <td><small>YES</small></td>
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* <td><small>NO</small></td>
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* <td><small>NO</small></td>
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* <td><small>NO</small></td>
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* <td style="text-align: left;">
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* Unsafe because fragmentation, not constant time, cannot be used
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* from IRQ handlers and not thread safe. The C runtime must also be
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* modified in order to work with the other allocators.
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* </td>
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* </tr>
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* </table>
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* <br>
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* When designing a system it is recommended to proceed as follow:
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* -# Use static objects and initializers whenever possible.
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* -# Where dynamic allocation is required without have to free the allocated
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* memory then use the Core Memory Manager allocation APIs.
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* -# Where dynamic allocation is required evaluate if one or more memory
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* pools can be used.
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* -# If all the above points do not satisfy your requirements then use the
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* heap allocator.
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* -# Consider the C-runtime allocator only for legacy code.
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* .
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*/
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