mm/mm_granalloc.c

/****************************************************************************
 * mm/mm_granalloc.c
 *
 *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

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

#include <nuttx/config.h>

#include <assert.h>

#include <nuttx/gran.h>

#include "mm_gran.h"

#ifdef CONFIG_GRAN

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/****************************************************************************
 * Name: gran_common_alloc
 *
 * Description:
 *   Allocate memory from the granule heap.
 *
 * Input Parameters:
 *   priv  - The granule heap state structure.
 *   alloc - The adress of the allocation.
 *   ngranules - The number of granules allocated
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static inline void gran_mark_allocated(FAR struct gran_s *priv,
                                       uintptr_t alloc,
                                       unsigned int ngranules)
{
  unsigned int granno;
  unsigned int gatidx;
  unsigned int gatbit;
  unsigned int avail;
  uint32_t     gatmask;

  /* Determine the granule number of the allocation */

  granno = (alloc - priv->heapstart) >> priv->log2gran;

  /* Determine the GAT table index associated with the allocation */

  gatidx = granno >> 5;
  gatbit = granno & 31;

  /* Mark bits in the GAT entry or entries */

  avail = 32 - gatbit;
  if (ngranules > avail)
    {
      /* Mark bits in the first GAT entry */

      gatmask =0xffffffff << gatbit;
      DEBUGASSERT((priv->gat[gatidx] & gatmask) == 0);

      priv->gat[gatidx] |= gatmask;
      ngranules -= avail;

      /* Mark bits in the second GAT entry */

      gatmask = 0xffffffff >> (32 - ngranules);
      DEBUGASSERT((priv->gat[gatidx+1] & gatmask) == 0);

      priv->gat[gatidx+1] |= gatmask;
    }

  /* Handle the case where where all of the granules come from one entry */

  else
    {
      /* Mark bits in a single GAT entry */

      gatmask   = 0xffffffff >> (32 - ngranules);
      gatmask <<= gatbit;
      DEBUGASSERT((priv->gat[gatidx] & gatmask) == 0);

      priv->gat[gatidx] |= gatmask;
      return;
    }

}

/****************************************************************************
 * Name: gran_common_alloc
 *
 * Description:
 *   Allocate memory from the granule heap.
 *
 * Input Parameters:
 *   priv - The granule heap state structure.
 *   size - The size of the memory region to allocate.
 *
 * Returned Value:
 *   On success, a non-NULL pointer to the allocated memory is returned.
 *
 ****************************************************************************/

static inline FAR void *gran_common_alloc(FAR struct gran_s *priv, size_t size)
{
  unsigned int ngranules;
  size_t       tmpmask;
  uintptr_t    alloc;
  uint32_t     curr;
  uint32_t     next;
  uint32_t     mask;
  int          granidx;
  int          gatidx;
  int          bitidx;
  int          shift;

  DEBUGASSERT(priv && size <= 32 * (1 << priv->log2gran));

  if (priv && size > 0)
    {
      /* Get exclusive access to the GAT */

      gran_enter_critical(priv);

      /* How many contiguous granules we we need to find? */

      tmpmask   = (1 << priv->log2gran) - 1;
      ngranules = (size + tmpmask) >> priv->log2gran;

      /* Then create mask for that number of granules */

      DEBUGASSERT(ngranules <= 32);
      mask = 0xffffffff >> (32 - ngranules);

      /* Now search the granule allocation table for that number of contiguous */

      alloc = priv->heapstart;

      for (granidx = 0; granidx < priv->ngranules; granidx += 32)
        {
          /* Get the GAT index associated with the granule table entry */

          gatidx = granidx >> 5;
          curr = priv->gat[gatidx];

          /* Handle the case where there are no free granules in the entry */

          if (curr == 0xffffffff)
            {
              alloc += (32 << priv->log2gran);
              continue;
            }

          /* Get the next entry from the GAT to support a 64 bit shift */

          if (granidx < priv->ngranules)
            {
              next = priv->gat[gatidx + 1];
            }

          /* Use all ones when are at the last entry in the GAT (meaning
           * nothing can be allocated.
           */

          else
            {
              next = 0xffffffff;
            }

          /* Search through the allocations in the 'curr' GAT entry
           * to see if we can satisfy the allocation starting in that
           * entry.
           *
           * This loop continues until either all of the bits have been
           * examined (bitidx >= 32), or until there are insufficient
           * granules left to satisfy the allocation.
           */

          for (bitidx = 0;
               bitidx < 32 && (granidx + bitidx + ngranules) <= priv->ngranules;
              )
            {
              /* Break out if there are no further free bits in 'curr'.
               * All of the zero bits might have gotten shifted out.
               */

              if (curr == 0xffffffff)
                {
                  break;
                }

              /* Check for the first zero bit in the lower or upper 16-bits.
               * From the test above, we know that at least one of the 32-
               * bits in 'curr' is zero.
               */

              else if ((curr & 0x0000ffff) == 0x0000ffff)
                {
                  /* Not in the lower 16 bits.  The first free bit must be
                   * in the upper 16 bits.
                   */

                  shift = 16;
                }

              /* We know that the first free bit is now within the lower 16
               * bits of 'curr'.  Is it in the upper or lower byte?
               */

              else if ((curr & 0x0000ff) == 0x000000ff)
                {
                  /* Not in the lower 8 bits.  The first free bit must be in
                   * the upper 8 bits.
                   */

                  shift = 8;
                }

              /* We know that the first free bit is now within the lower 4
               * bits of 'curr'.  Is it in the upper or lower nibble?
               */

              else if ((curr & 0x00000f) == 0x0000000f)
                {
                  /* Not in the lower 4 bits.  The first free bit must be in
                   * the upper 4 bits.
                   */

                  shift = 4;
                }

              /* We know that the first free bit is now within the lower 4 bits
               * of 'curr'.  Is it in the upper or lower pair?
               */

              else if ((curr & 0x000003) == 0x00000003)
                {
                  /* Not in the lower 2 bits.  The first free bit must be in
                   * the upper 2 bits.
                   */

                  shift = 2;
                }

              /* We know that the first free bit is now within the lower 4 bits
               * of 'curr'.  Check if we have the allocation at this bit position.
               */

              else if ((curr & mask) == 0)
                {
                  /* Yes.. mark these granules allocated */

                  gran_mark_allocated(priv, alloc, ngranules);

                  /* And return the allocation address */

                  gran_leave_critical(priv);
                  return (FAR void *)alloc;
                }

              /* The free allocation does not start at this position */

              else
                {
                  shift = 1;
                }

              /* Set up for the next time through the loop.  Perform a 64
               * bit shift to move to the next gram position andi ncrement
               * to the next candidate allocation address.
               */

              alloc  += (shift << priv->log2gran);
              curr    = (curr >> shift) | (next << (32 - shift));
              next  >>= shift;
              bitidx += shift;
            }
        }
    }

  gran_leave_critical(priv);
  return NULL;
}

/****************************************************************************
 * Global Functions
 ****************************************************************************/

/****************************************************************************
 * Name: gran_alloc
 *
 * Description:
 *   Allocate memory from the granule heap.
 *
 *   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:
 *   handle - The handle previously returned by gran_initialize
 *   size   - The size of the memory region to allocate.
 *
 * Returned Value:
 *   On success, either a non-NULL pointer to the allocated memory (if
 *   CONFIG_GRAN_SINGLE) or zero  (if !CONFIG_GRAN_SINGLE) is returned.
 *
 ****************************************************************************/

#ifdef CONFIG_GRAN_SINGLE
FAR void *gran_alloc(size_t size)
{
  return gran_common_alloc(g_graninfo, size);
}
#else
FAR void *gran_alloc(GRAN_HANDLE handle, size_t size)
{
  return gran_common_alloc((FAR struct gran_s *)handle, size);
}
#endif

#endif /* CONFIG_GRAN */