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[DOCS] MM - Added memory manager overview.
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‎_includes/docs_contents.html

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@@ -46,6 +46,10 @@ <h4>API</h4>
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<a href="{{ site.url }}/docs/api/i2c">I2C Subsystem</a>
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</li>
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<li class="{% if page.title == "Memory Manager" %}current{% endif %}">
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<a href="{{ site.url }}/docs/api/mm">Memory Manager</a>
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</li>
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<li class="{% if page.title == "Processes and Threads" %}current{% endif %}">
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<a href="{{ site.url }}/docs/api/process">Processes and Threads</a>
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</li>
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<a href="{{ site.url }}/docs/api/semaphore">Semaphores & Mutex's</a>
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</li>
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<li class="{% if page.title == "Syslog" %}current{% endif %}">
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<a href="{{ site.url }}/docs/api/syslog">Syslog</a>
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</li>
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<li class="{% if page.title == "Time & Timers" %}current{% endif %}">
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<a href="{{ site.url }}/docs/api/timers">Time & Timers</a>
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</li>
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<li class="{% if page.title == "Watchdog" %}current{% endif %}">
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<a href="{{ site.url }}/docs/api/watchdog">Watchdog</a>
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</li>

‎docs/mm/mm.md

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---
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layout: docs
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title: Memory Manager
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next_section: usage-rules
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permalink: /docs/api/mm/
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header_path: os/include/mm/bt_mm.h
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source_path: os/src/mm/bt_mm.c
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---
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The memory manager is responsible for managing all memory within BitThunder. For systems with MMU's the mm,
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is also responsible for managing all virtual memory mappings for each process.
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# User-space Memory Allocation API.
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<div class="mobile-side-scroller">
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<table>
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<thead>
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<tr>
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<th>API</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><p><code><a href="{{ site.url }}/api/mm/malloc/">malloc()</a></code></p></td>
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<td><p>
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POSIX compliant malloc implementation.
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</p></td>
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</tr>
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<tr>
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<td><p><code><a href="{{ site.url }}/api/mm/free/">free()</a></code></p></td>
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<td><p>
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POSIX compliant free implementation.
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</p></td>
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</tr>
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</tbody>
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</table>
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</div>
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# Kernel-mode API.
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<div class="mobile-side-scroller">
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<table>
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<thead>
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<tr>
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<th>API</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><p><code><a href="{{ site.url }}/api/mm/bt_kmalloc/">BT_kMalloc()</a></code></p></td>
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<td><p>
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Allocates arbitrary amounts of memory for use in the kernel, e.g. drivers etc.
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</p></td>
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</tr>
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<tr>
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<td><p><code><a href="{{ site.url }}/api/mm/bt_kfree/">BT_kFree()</a></code></p></td>
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<td><p>
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Frees a kernel memory allocation.
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</p></td>
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</tr>
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<tr>
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<td><p><code><a href="{{ site.url }}/api/mm/bt_ioremap/">bt_ioremap()</a></code></p></td>
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<td><p>
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Remaps a physical address to a usable virtual address. THIS MUST BE USED EVEN WITH NO MMU.
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</p></td>
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</tr>
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</tbody>
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</table>
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</div>
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# Page Allocation
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<div class="mobile-side-scroller">
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<table>
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<thead>
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<tr>
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<th>API</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><p><code><a href="{{ site.url }}/api/mm/bt_page_alloc/">bt_page_alloc()</a></code></p></td>
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<td><p>
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Allocates page-aligned, page multiples of atleast the requested size.
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</p></td>
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</tr>
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<tr>
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<td><p><code><a href="{{ site.url }}/api/mm/bt_page_free/">bt_page_free()</a></code></p></td>
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<td><p>
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Frees page-aligned memory as requested from bt_page_alloc().
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</p></td>
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</tr>
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</tbody>
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</table>
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</div>
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# Design Overview
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The memory manager has a few different implementations which are used depending on the kernel configurations.
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## Basic MM
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Typical micro-controller applications use a mono-lithic, space-efficient heap.
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The heap consists of a free linked list, and the heap structure is stored within the heaps memory
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directly. This means its possible for threads/processes to cause heap corruption.
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## Powerful MM (Page based and Virtual Memory Management)
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In these more powerful systems with MMUs, its possible to configure support for page based memory allocations
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and optionally virtual memory if desired.
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The page based allocator becomes the lowest-level memory allocator on which the kernel heap, and process heaps
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are based.
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The kernel heap is really efficient SLAB based algorithm, with all O(1) constant time operations.
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# To be implemented:
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* mmap()
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* User-space heaps.
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# In progress
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* vmalloc() api - Virtual memory allocation and mappings.
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# Further Reading
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The full API is defined under:
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{% include api/header-path.md %}
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See the implementation under:
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{% include api/source-path.md %}
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<a href="{{ site.gh-blob-url }}/os/src/mm/slab.c"><code>os/src/mm/slab.c</code></a>
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<a href="{{ site.gh-blob-url }}/os/src/mm/bt_page.c"><code>os/src/mm/bt_page.c</code></a>

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