nuttx/mm/mm_gran/mm_graninit.c

/****************************************************************************
 * mm/mm_gran/mm_graninit.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <assert.h>
#include <errno.h>

#include <nuttx/mm/gran.h>
#include <nuttx/kmalloc.h>

#include "mm_gran/mm_gran.h"

#ifdef CONFIG_GRAN

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: gran_initialize
 *
 * Description:
 *   Set up one granule allocator instance.  Allocations will be aligned to
 *   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 quantization waste.
 *   Additional memory waste can occur from alignment; log2align should be
 *   set to 0 unless you are using the granule allocator to manage DMA
 *   or page-aligned memory and your hardware has specific memory alignment
 *   requirements.
 *
 *   General 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] locate_data(.dmaheap);
 *
 *   The heap is created by calling gran_initialize().  Here the granule size
 *   is set to 64 bytes (2**6) and the alignment to 16 bytes (2**4):
 *
 *     GRAN_HANDLE handle = gran_initialize(g_dmaheap, DMAHEAP_SIZE, 6, 4);
 *
 *   Then the GRAN_HANDLE can be used to allocate memory:
 *
 *     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
 *   additional coding effort.
 *
 * Input Parameters:
 *   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->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
 *   granule allocator interfaces.
 *
 ****************************************************************************/

GRAN_HANDLE gran_initialize(FAR void *heapstart, size_t heapsize,
                            uint8_t log2gran, uint8_t log2align)
{
  FAR struct gran_s *priv;
  uintptr_t          heapend;
  uintptr_t          alignedstart;
  unsigned int       mask;
  unsigned int       alignedsize;
  unsigned int       ngranules;

  /* Check parameters if debug is on.  Note the size of a granule is
   * limited to 2**31 bytes and that the size of the granule must be greater
   * than or equal to the alignment size.
   */

  DEBUGASSERT(heapstart && heapsize > 0 &&
              log2gran > 0 && log2gran < 32 &&
              log2gran >= log2align);

  /* Get the aligned start of the heap */

  mask         = (1 << log2align) - 1;
  alignedstart = ((uintptr_t)heapstart + mask) & ~mask;

  /* Determine the number of granules */

  mask         = (1 << log2gran) - 1;
  heapend      = (uintptr_t)heapstart + heapsize;
  alignedsize  = (heapend - alignedstart) & ~mask;
  ngranules    = alignedsize >> log2gran;

  /* Allocate the information structure with a granule table of the
   * correct size.
   */

  priv = (FAR struct gran_s *)kmm_zalloc(SIZEOF_GRAN_S(ngranules));
  if (priv)
    {
      /* Initialize non-zero elements of the granules heap info structure */

      priv->log2gran  = log2gran;
      priv->ngranules = ngranules;
      priv->heapstart = alignedstart;

      /* Initialize mutual exclusion support */

#ifndef CONFIG_GRAN_INTR
      nxsem_init(&priv->exclsem, 0, 1);
#endif
    }

  return (GRAN_HANDLE)priv;
}

#endif /* CONFIG_GRAN */