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diff --git a/nuttx/mm/README.txt b/nuttx/mm/README.txt new file mode 100644 index 000000000..b0b80deae --- /dev/null +++ b/nuttx/mm/README.txt @@ -0,0 +1,71 @@ +mm/README.txt +============= + +This directory contains the NuttX memory management logic. This include: + +1) The standard memory management functions as prototyped in stdlib.h as + specified in the Base definitions volume of IEEE Std 1003.1-2001. This + include the files: + + o Standard Interfaces: mm_malloc.c, mm_calloc.c, mm_realloc.c, + mm_memalign.c, mm_free.c + o Less-Standard Interfaces: mm_zalloc.c, mm_mallinfo.c + o Internal Implementation: mm_initialize.c mm_sem.c mm_addfreechunk.c + mm_size2ndx.c mm_shrinkchunk.c, mm_internal.h + o Build and Configuration files: Kconfig, Makefile + + Memory Models: + + o Small Memory Model. If the MCU supports only 16-bit data addressing + then the small memory model is automatically used. The maximum size + of the heap is then 64K. The small memory model can also be forced + MCUs with wider addressing by defining CONFIG_SMALL_MEMORY in the + NuttX configuration file. + o Large Memory Model. Otherwise, the allocator uses a model that + supports a heap of up to 4G. + + This implementation uses a variable length allocator with the following + properties: + + o Overhead: Either 8- or 4-bytes per allocation for large and small + models, respectively. + o Alignment: All allocations are aligned to 8- or 4-bytes for large + and small models, respectively. + +2) Test Program. There is also a host-best test program that can be + used to verify the memory manager. These are the file: + + Makefile.test, mm_test.c, and mm_environment.h. + + Build instructions: + + make -f Makefile.test + + The executable will be built in the top-level directory as nuttx/mm_text + (or mm_test.exe under Cygwin). + +3) Granule Allocator. A non-standard granule allocator is also available + in this directory The granule allocator allocates memory in units + of a fixed sized block ("granule"). All memory is aligned to the size + of one granule. + + The granule allocator interfaces are defined in nuttx/include/nuttx/gran.h. + The granule allocator consists of these files in this directory: + + mm_gran.h, mm_granalloc.c, mm_grancritical.c, mm_granfree.c + mm_graninit.c + + The granule allocator is not used anywhere within the base NuttX code + as of this writing. The intent of the granule allocator is to provide + a tool to support platform-specific management of aligned DMA memory. + + NOTE: Because each granule is aligned to the granule size and each + allocations is in units of the granule size, selection of the granule + size is important: Larger granules will give better performance and + less overhead but more losses of memory due to alignment and quantization + waste. + + The current implementation also restricts the maximum allocation size + to 32 granules. That restriction could be eliminated with some + additional coding effort, but currently requires larger granule + sizes for larger allocations. |