sralloc.c

zigbee 协议栈源代码。zigbee是轻量级无线网络协议

/*****************************************************************************
 *
 *              Simple SRAM Dynamic Memory Allocation
 *
 *****************************************************************************
 * FileName:        sralloc.c
 * Dependencies:
 * Processor:       PIC18F with CAN
 * Compiler:        C18 02.20.00 or higher
 * Linker:          MPLINK 03.40.00 or higher
 * Company:         Microchip Technology Incorporated
 *
 * Software License Agreement
 *
 * The software supplied herewith by Microchip Technology Incorporated
 * (the "Company") is intended and supplied to you, the Company's
 * customer, for use solely and exclusively with products manufactured
 * by the Company.
 *
 * The software is owned by the Company and/or its supplier, and is
 * protected under applicable copyright laws. All rights are reserved.
 * Any use in violation of the foregoing restrictions may subject the
 * user to criminal sanctions under applicable laws, as well as to
 * civil liability for the breach of the terms and conditions of this
 * license.
 *
 * THIS SOFTWARE IS PROVIDED IN AN "AS IS" CONDITION. NO WARRANTIES,
 * WHETHER EXPRESS, IMPLIED OR STATUTORY, INCLUDING, BUT NOT LIMITED
 * TO, IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE APPLY TO THIS SOFTWARE. THE COMPANY SHALL NOT,
 * IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL OR
 * CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
 *
 *
 * This is a simple dynamic memory allocation module. The following are the
 * supported services:
 *
 * unsigned char * NEAR SRAMalloc(NEAR unsigned char nBytes)
 * void SRAMfree(unsigned char * NEAR pSRAM)
 * void SRAMInitHeap(void)
 *
 * This version of the dynamic memory allocation limits the segment size
 * to 126 bytes. This is specifically designed such to enable better
 * performance by limiting pointer manipulation.
 *
 *
 * How it works:
 * The model is based on a simple form of a linked list. A block of memory
 * refered to as the dynamic heap is split into segments. Each segment
 * has a single byte header that references the next segment in the list
 * as well as indicating whether the segment is allocated. Consiquently
 * the reference implicitly identifies the length of the segment.
 *
 * This method also enables the possibility of allowing a large number
 * of memory allocations. The maximum is limited by the defined heap size.
 *
 * SRAMalloc() is used to split or merge segments to be allocated.
 * SRAMfree() is used to release segments.
 *
 * Example:
 *  ----------
 *  |  0x7F  |  0x200   Header Seg1
 *  |        |
 *  |        |
 *  |        |
 *  |        |
 *  |        |
 *  |        |
 *  |  0x89  |  0x27F   Header Seg2 (allocated)
 *  |        |
 *  |        |
 *  |  0x77  |  0x288   Header Seg3
 *  |        |
 *  |        |
 *  |        |
 *  |        |
 *  |        |
 *  |        |
 *  |        |
 *  |  0x00  |  0x2FF   Tail
 *  ----------
 *
 *
 *  Bit 7   Bit 6   Bit 5   Bit 4   Bit 3   Bit 2   Bit 1   Bit 0
 *
 *  Alloc   ------------- reference to next Header --------------
 *
 *
 * Recomendations:
 * Although this model will allow dynamic allocation down to a single byte,
 * doing so sacrifices performance. With more segments within the heap, more
 * time is required to attempt to allocate memory. Plus every segment requires
 * a header byte; therefore, smaller segments require more memory. There is
 * also the possibility of fragmentation, which could ultimately doom an
 * application by reducing the largest allocatable block of memory. Thus the
 * recomendation is to allocate at least 8 bytes of memory.
 *
 *
 *
 * Author               Date        Version     Comment
 *~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 * Ross Fosler          05/25/03    v1.03       ... First release
 * Nilesh Rajbharti     7/14/04                 Modified for Zigbee stack.
 * Nilesh Rajbharti     11/1/04                 Pre-release version
 *****************************************************************************/
#include "Zigbee.def"




#define NEAR


#define _MAX_SEGMENT_SIZE   32
#define _MAX_HEAP_SIZE  MAX_HEAP_SIZE-1




/*********************************************************************
 * Segment header data type
 ********************************************************************/
typedef union _SALLOC
{
    unsigned char byte;
    struct _BITS
    {
        unsigned count:7;
        unsigned alloc:1;
    }bits;
}SALLOC;





/*********************************************************************
 * Reserve the memory heap
 ********************************************************************/
unsigned char _uDynamicHeap[MAX_HEAP_SIZE];


/*********************************************************************
 * Private function declarations
 ********************************************************************/
NEAR unsigned char _SRAMmerge(SALLOC * NEAR pSegA);




/*********************************************************************
 * Function:        unsigned char * SRAMalloc(unsigned char length)
 *
 * PreCondition:    A memory block must be allocated in the linker,
 *                  and the memory headers and tail must already be
 *                  set via the function SRAMInitHeap().
 *
 * Input:           unsigned char nBytes - Number of bytes to allocate.
 *
 * Output:          unsigned char * - A pointer to the requested block
 *                  of memory.
 *
 * Side Effects:
 *
 * Overview:        This functions allocates a chunk of memory from
 *                  the heap. The maximum segment size for this
 *                  version is 126 bytes. If the heap does not have
 *                  an available segment of sufficient size it will
 *                  attempt to create a segment; otherwise a NULL
 *                  pointer is returned. If allocation is succeessful
 *                  then a pointer to the requested block is returned.
 *
 * Note:            The calling function must maintain the pointer
 *                  to correctly free memory at runtime.
 ********************************************************************/
unsigned char * NEAR SRAMalloc(NEAR unsigned char nBytes)
{
    SALLOC * NEAR pHeap;
    SALLOC * NEAR temp;
    NEAR SALLOC segHeader;
    NEAR unsigned char segLen;

    // Do not allow allocation above the max minus one bytes
    if (nBytes > (_MAX_SEGMENT_SIZE - 1)) return (0);

    // Init the pointer to the heap
    pHeap = (SALLOC *)_uDynamicHeap;

    while (1)
    {
        // Get the header of the segment
        segHeader = *pHeap;

        // Extract the segment length from the segment
        segLen = segHeader.bits.count - 1;

        // A null segment indicates the end of the table
        if (segHeader.byte == 0) return (0);

        // If this segment is not allocated then attempt to allocate it
        if (!(segHeader.bits.alloc))
        {
            // If the free segment is too small then attempt to merge
            if (nBytes > segLen)
            {
                // If the merge fails them move on to the next segment
                if (!(_SRAMmerge(pHeap))) pHeap += segHeader.bits.count;
            }
            else

            // If the segment length matches the request then allocate the
            // header and return the pointer
            if (nBytes == segLen)
            {
                // Allocate the segment
                (*pHeap).bits.alloc = 1;

                // Return the pointer to the caller
                return ((unsigned char *)(pHeap + 1));
            }

            // Else create a new segment
            else
            {
                // Reset the header to point to a new segment
                (*pHeap).byte = nBytes + 0x81;

                // Remember the pointer to the first segment
                temp = pHeap + 1;

                // Point to the new segment
                pHeap += (nBytes + 1);

                // Insert the header for the new segment
                (*pHeap).byte = segLen - nBytes;

                // Return the pointer to the user
                return ((unsigned char *) temp);
            }
        }

        // else set the pointer to the next segment header in the heap
        else
        {
            pHeap += segHeader.bits.count;
        }
    }

    return (0);
}



/*********************************************************************
 * Function:        void SRAMfree(unsigned char * pSRAM)
 *
 * PreCondition:    The pointer must have been returned from a
 *                  previously allocation via SRAMalloc().
 *
 * Input:           unsigned char * pSRAM - pointer to the allocated
 *
 * Output:          void
 *
 * Side Effects:
 *
 * Overview:        This function de-allocates a previously allocated
 *                  segment of memory.
 *
 * Note:            The pointer must be a valid pointer returned from
 *                  SRAMalloc(); otherwise, the segment may not be
 *                  successfully de-allocated, and the heap may be
 *                  corrupted.
 ********************************************************************/
void SRAMfree(unsigned char * NEAR pSRAM)
{
    // Release the segment
    (*(SALLOC *)(pSRAM - 1)).bits.alloc = 0;
}



/*********************************************************************
 * Function:        void SRAMInitHeap(void)
 *
 * PreCondition:
 *
 * Input:           void
 *
 * Output:          void
 *
 * Side Effects:
 *
 * Overview:        This function initializes the dynamic heap. It
 *                  inserts segment headers to maximize segment space.
 *
 * Note:            This function must be called at least one time.
 *                  And it could be called more times to reset the
 *                  heap.
 ********************************************************************/
void SRAMInitHeap(void)
{
    unsigned char * NEAR pHeap;
    NEAR unsigned int count;

    pHeap = _uDynamicHeap;
    count = _MAX_HEAP_SIZE;

    while (1)
    {
        if (count > _MAX_SEGMENT_SIZE)
        {
            *pHeap = _MAX_SEGMENT_SIZE;
            pHeap += _MAX_SEGMENT_SIZE;
            count = count - _MAX_SEGMENT_SIZE;
        }
        else
        {
            *pHeap = count;
            *(pHeap + count) = 0;
            return;
        }
    }
}




/*********************************************************************
 * Function:        unsigned char _SRAMmerge(SALLOC * NEAR pSegA)
 *
 * PreCondition:
 *
 * Input:           SALLOC * NEAR pSegA - pointer to the first segment.
 *
 * Output:          usnigned char - returns the length of the
 *                  merged segment or zero if failed to merge.
 *
 * Side Effects:
 *
 * Overview:        This function tries to merge adjacent segments
 *                  that have not been allocated. The largest possible
 *                  segment is merged if possible.
 *
 * Note:
 ********************************************************************/
NEAR unsigned char _SRAMmerge(SALLOC * NEAR pSegA)
{
    SALLOC * NEAR pSegB;
    NEAR SALLOC uSegA, uSegB, uSum;


    // Init the pointer to the heap
    pSegB = pSegA + (*pSegA).byte;

    // Extract the headers for faster processing
    uSegA = *pSegA;
    uSegB = *pSegB;

    // Quit if the tail has been found
    if (uSegB.byte == 0) return (0);

    // If either segment is allocated then do not merge
    if (uSegA.bits.alloc || uSegB.bits.alloc) return (0);

    // If the first segment is max then nothing to merge
    if (uSegA.bits.count == _MAX_SEGMENT_SIZE) return (0);

    // Get the sum of the two segments
    uSum.byte = uSegA.byte + uSegB.byte;


    // If the sum of the two segments are > than the largest segment
    // then create a new segment equal to the max segment size and
    // point to the next segments
    if ((uSum.byte) > _MAX_SEGMENT_SIZE)
    {
        (*pSegA).byte = _MAX_SEGMENT_SIZE;
        pSegA += _MAX_SEGMENT_SIZE; //(*pSeg1).byte;
        pSegB += uSegB.byte; //(*pSeg2).byte ;
        (*pSegA).byte = pSegB - pSegA;

        return (_MAX_SEGMENT_SIZE);
    }
    // Else combine the two segments into one segment and
    // do not adjust the pointers to the next segment
    else
    {
        return ((*pSegA).byte = uSum.byte);
    }
}