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author | patacongo <patacongo@7fd9a85b-ad96-42d3-883c-3090e2eb8679> | 2012-09-14 18:14:40 +0000 |
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committer | patacongo <patacongo@7fd9a85b-ad96-42d3-883c-3090e2eb8679> | 2012-09-14 18:14:40 +0000 |
commit | 2c2ba7f0c5f99aef3fac0eaa8a2c7a79c5faa74d (patch) | |
tree | 42e784046dde6eabe94ecb7922a0abf494592d8c /nuttx/include | |
parent | 857d2a770b39162c43604bfc1cccf431d592ff9b (diff) | |
download | px4-firmware-2c2ba7f0c5f99aef3fac0eaa8a2c7a79c5faa74d.tar.gz px4-firmware-2c2ba7f0c5f99aef3fac0eaa8a2c7a79c5faa74d.tar.bz2 px4-firmware-2c2ba7f0c5f99aef3fac0eaa8a2c7a79c5faa74d.zip |
Missed one file in last checking; Gran allocator alignment decoupled from granule size
git-svn-id: https://nuttx.svn.sourceforge.net/svnroot/nuttx/trunk@5152 7fd9a85b-ad96-42d3-883c-3090e2eb8679
Diffstat (limited to 'nuttx/include')
-rw-r--r-- | nuttx/include/nuttx/gran.h | 41 |
1 files changed, 35 insertions, 6 deletions
diff --git a/nuttx/include/nuttx/gran.h b/nuttx/include/nuttx/gran.h index f3a6d0fe9..5390618a3 100644 --- a/nuttx/include/nuttx/gran.h +++ b/nuttx/include/nuttx/gran.h @@ -90,9 +90,32 @@ extern "C" { * * Description: * Set up one granule allocator instance. Allocations will be aligned to - * the granule size; allocations will be in units of the granule size. - * Larger granules will give better performance and less overhead but more - * losses of memory due to alignment and quantization waste. + * the alignment size (log2align; allocations will be in units of the + * granule size (log2gran). Larger granules will give better performance + * and less overhead but more losses of memory due to alignment + * quantization waste. Additional memory waste can occur form alignment; + * log2align should be set to 0 unless you are using the granule allocator + * to manage DMA memory and your hardware has specific memory alignment + * requirements. + * + * Geneneral Usage Summary. This is an example using the GCC section + * attribute to position a DMA heap in memory (logic in the linker script + * would assign the section .dmaheap to the DMA memory. + * + * FAR uint32_t g_dmaheap[DMAHEAP_SIZE] __attribute__((section(.dmaheap))); + * + * The heap is created by calling gran_initialize. Here the granual size + * is set to 64 bytes and the alignment to 16 bytes: + * + * GRAN_HANDLE handle = gran_initialize(g_dmaheap, DMAHEAP_SIZE, 6, 4); + * + * Then the GRAN_HANDLE can be used to allocate memory (There is no + * GRAN_HANDLE if CONFIG_GRAN_SINGLE=y): + * + * FAR uint8_t *dma_memory = (FAR uint8_t *)gran_alloc(handle, 47); + * + * The actual memory allocates will be 64 byte (wasting 17 bytes) and + * will be aligned at least to (1 << log2align). * * NOTE: The current implementation also restricts the maximum allocation * size to 32 granules. That restriction could be eliminated with some @@ -102,7 +125,13 @@ extern "C" { * heapstart - Start of the granule allocation heap * heapsize - Size of heap in bytes * log2gran - Log base 2 of the size of one granule. 0->1 byte, - * 1->2 bytes, 2->4 bytes, 3-> 8bytes, etc. + * 1->2 bytes, 2->4 bytes, 3-> 8 bytes, etc. + * log2align - Log base 2 of required alignment. 0->1 byte, + * 1->2 bytes, 2->4 bytes, 3-> 8 bytes, etc. Note that + * log2gran must be greater than or equal to log2align + * so that all contiguous granules in memory will meet + * the minimum alignment requirement. A value of zero + * would mean that no alignment is required. * * Returned Value: * On success, a non-NULL handle is returned that may be used with other @@ -112,10 +141,10 @@ extern "C" { #ifdef CONFIG_GRAN_SINGLE EXTERN int gran_initialize(FAR void *heapstart, size_t heapsize, - uint8_t log2gran); + uint8_t log2gran, uint8_t log2align); #else EXTERN GRAN_HANDLE gran_initialize(FAR void *heapstart, size_t heapsize, - uint8_t log2gran); + uint8_t log2gran, uint8_t log2align); #endif /**************************************************************************** |