File content as of revision 1:8aa5cdb4ab67:

/*
The MIT License (MIT)

Copyright (c) 2016 British Broadcasting Corporation.
This software is provided by Lancaster University by arrangement with the BBC.

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the "Software"),
to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
*/

/**
  * A simple 32 bit block based memory allocator. This allows one or more memory segments to
  * be designated as heap storage, and is designed to run in a static memory area or inside the standard C
  * heap for use by the micro:bit runtime. This is required for several reasons:
  *
  * 1) It reduces memory fragmentation due to the high churn sometime placed on the heap
  * by ManagedTypes, fibers and user code. Underlying heap implentations are often have very simplistic
  * allocation pilicies and suffer from fragmentation in prolonged use - which can cause programs to
  * stop working after a period of time. The algorithm implemented here is simple, but highly tolerant to
  * large amounts of churn.
  *
  * 2) It allows us to reuse the 8K of SRAM set aside for SoftDevice as additional heap storage
  * when BLE is not in use.
  *
  * 3) It gives a simple example of how memory allocation works! :-)
  *
  * P.S. This is a very simple allocator, therefore not without its weaknesses. Why don't you consider
  * what these are, and consider the tradeoffs against simplicity...
  *
  * @note The need for this should be reviewed in the future, if a different memory allocator is
  * made availiable in the mbed platform.
  *
  * TODO: Consider caching recently freed blocks to improve allocation time.
  */

#include "MicroBitConfig.h"
#include "MicroBitHeapAllocator.h"
#include "MicroBitDevice.h"
#include "ErrorNo.h"

struct HeapDefinition
{
    uint32_t *heap_start;		// Physical address of the start of this heap.
    uint32_t *heap_end;		    // Physical address of the end of this heap.
};

// A list of all active heap regions, and their dimensions in memory.
HeapDefinition heap[MICROBIT_MAXIMUM_HEAPS] = { };
uint8_t heap_count = 0;

#if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
// Diplays a usage summary about a given heap...
void microbit_heap_print(HeapDefinition &heap)
{
	uint32_t	blockSize;
	uint32_t	*block;
    int         totalFreeBlock = 0;
    int         totalUsedBlock = 0;
    int         cols = 0;

    if (heap.heap_start == NULL)
    {
        if(SERIAL_DEBUG) SERIAL_DEBUG->printf("--- HEAP NOT INITIALISED ---\n");
        return;
    }

    if(SERIAL_DEBUG) SERIAL_DEBUG->printf("heap_start : %p\n", heap.heap_start);
    if(SERIAL_DEBUG) SERIAL_DEBUG->printf("heap_end   : %p\n", heap.heap_end);
    if(SERIAL_DEBUG) SERIAL_DEBUG->printf("heap_size  : %d\n", (int)heap.heap_end - (int)heap.heap_start);

	// Disable IRQ temporarily to ensure no race conditions!
    __disable_irq();

	block = heap.heap_start;
	while (block < heap.heap_end)
	{
		blockSize = *block & ~MICROBIT_HEAP_BLOCK_FREE;
        if(SERIAL_DEBUG) SERIAL_DEBUG->printf("[%c:%d] ", *block & MICROBIT_HEAP_BLOCK_FREE ? 'F' : 'U', blockSize*4);
        if (cols++ == 20)
        {
            if(SERIAL_DEBUG) SERIAL_DEBUG->printf("\n");
            cols = 0;
        }

        if (*block & MICROBIT_HEAP_BLOCK_FREE)
            totalFreeBlock += blockSize;
        else
            totalUsedBlock += blockSize;

		block += blockSize;
    }

	// Enable Interrupts
    __enable_irq();

    if(SERIAL_DEBUG) SERIAL_DEBUG->printf("\n");

    if(SERIAL_DEBUG) SERIAL_DEBUG->printf("mb_total_free : %d\n", totalFreeBlock*4);
    if(SERIAL_DEBUG) SERIAL_DEBUG->printf("mb_total_used : %d\n", totalUsedBlock*4);
}


// Diagnostics function. Displays a usage summary about all initialised heaps.
void microbit_heap_print()
{
    for (int i=0; i < heap_count; i++)
    {
        if(SERIAL_DEBUG) SERIAL_DEBUG->printf("\nHEAP %d: \n", i);
        microbit_heap_print(heap[i]);
    }
}
#endif

void microbit_initialise_heap(HeapDefinition &heap)
{
    // Simply mark the entire heap as free.
    *heap.heap_start = ((uint32_t) heap.heap_end - (uint32_t) heap.heap_start) / MICROBIT_HEAP_BLOCK_SIZE;
    *heap.heap_start |= MICROBIT_HEAP_BLOCK_FREE;
}

/**
  * Create and initialise a given memory region as for heap storage.
  * After this is called, any future calls to malloc, new, free or delete may use the new heap.
  * The heap allocator will attempt to allocate memory from heaps in the order that they are created.
  * i.e. memory will be allocated from first heap created until it is full, then the second heap, and so on.
  *
  * @param start The start address of memory to use as a heap region.
  *
  * @param end The end address of memory to use as a heap region.
  *
  * @return MICROBIT_OK on success, or MICROBIT_NO_RESOURCES if the heap could not be allocated.
  *
  * @note Only code that #includes MicroBitHeapAllocator.h will use this heap. This includes all micro:bit runtime
  * code, and user code targetting the runtime. External code can choose to include this file, or
  * simply use the standard heap.
  */
int microbit_create_heap(uint32_t start, uint32_t end)
{
    // Ensure we don't exceed the maximum number of heap segments.
    if (heap_count == MICROBIT_MAXIMUM_HEAPS)
        return MICROBIT_NO_RESOURCES;

    // Sanity check. Ensure range is valid, large enough and word aligned.
    if (end <= start || end - start < MICROBIT_HEAP_BLOCK_SIZE*2 || end % 4 != 0 || start % 4 != 0)
        return MICROBIT_INVALID_PARAMETER;

	// Disable IRQ temporarily to ensure no race conditions!
    __disable_irq();

    // Record the dimensions of this new heap
    heap[heap_count].heap_start = (uint32_t *)start;
    heap[heap_count].heap_end = (uint32_t *)end;

    // Initialise the heap as being completely empty and available for use.
    microbit_initialise_heap(heap[heap_count]);
    heap_count++;

	// Enable Interrupts
    __enable_irq();

#if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
    microbit_heap_print();
#endif

    return MICROBIT_OK;
}

/**
  * Create and initialise a heap region within the current the heap region specified
  * by the linker script.
  *
  * If the requested amount is not available, then the amount requested will be reduced
  * automatically to fit the space available.
  *
  * @param ratio The proportion of the underlying heap to allocate.
  *
  * @return MICROBIT_OK on success, or MICROBIT_NO_RESOURCES if the heap could not be allocated.
  */
int microbit_create_nested_heap(float ratio)
{
    uint32_t length;
    void *p;

    if (ratio <= 0.0 || ratio > 1.0)
        return MICROBIT_INVALID_PARAMETER;

    // Snapshot something at the top of the main heap.
    p = native_malloc(sizeof(uint32_t));

    // Estimate the size left in our heap, taking care to ensure it lands on a word boundary.
    length = (uint32_t) (((float)(MICROBIT_HEAP_END - (uint32_t)p)) * ratio);
    length &= 0xFFFFFFFC;

    // Release our reference pointer.
    native_free(p);
    p = NULL;

    // Allocate memory for our heap.
    // We iteratively reduce the size of memory are allocate until it fits within available space.
    while (p == NULL)
    {
        p = native_malloc(length);
        if (p == NULL)
        {
            length -= 32;
            if (length <= 0)
                return MICROBIT_NO_RESOURCES;
        }
    }

    uint32_t start = (uint32_t) p;
    microbit_create_heap(start, start + length);

    return MICROBIT_OK;
}

/**
  * Attempt to allocate a given amount of memory from any of our configured heap areas.
  *
  * @param size The amount of memory, in bytes, to allocate.
  *
  * @return A pointer to the allocated memory, or NULL if insufficient memory is available.
  */
void *microbit_malloc(size_t size, HeapDefinition &heap)
{
	uint32_t	blockSize = 0;
	uint32_t	blocksNeeded = size % MICROBIT_HEAP_BLOCK_SIZE == 0 ? size / MICROBIT_HEAP_BLOCK_SIZE : size / MICROBIT_HEAP_BLOCK_SIZE + 1;
	uint32_t	*block;
	uint32_t	*next;

	if (size <= 0)
		return NULL;

	// Account for the index block;
	blocksNeeded++;

	// Disable IRQ temporarily to ensure no race conditions!
    __disable_irq();

	// We implement a first fit algorithm with cache to handle rapid churn...
    // We also defragment free blocks as we search, to optimise this and future searches.
	block = heap.heap_start;
	while (block < heap.heap_end)
	{
		// If the block is used, then keep looking.
		if(!(*block & MICROBIT_HEAP_BLOCK_FREE))
		{
			block += *block;
			continue;
		}

		blockSize = *block & ~MICROBIT_HEAP_BLOCK_FREE;

		// We have a free block. Let's see if the subsequent ones are too. If so, we can merge...
		next = block + blockSize;

		while (*next & MICROBIT_HEAP_BLOCK_FREE)
		{
			if (next >= heap.heap_end)
				break;

			// We can merge!
			blockSize += (*next & ~MICROBIT_HEAP_BLOCK_FREE);
			*block = blockSize | MICROBIT_HEAP_BLOCK_FREE;

			next = block + blockSize;
		}

		// We have a free block. Let's see if it's big enough.
        // If so, we have a winner.
		if (blockSize >= blocksNeeded)
			break;

		// Otherwise, keep looking...
		block += blockSize;
	}

	// We're full!
	if (block >= heap.heap_end)
    {
        __enable_irq();
        return NULL;
    }

	// If we're at the end of memory or have very near match then mark the whole segment as in use.
	if (blockSize <= blocksNeeded+1 || block+blocksNeeded+1 >= heap.heap_end)
	{
		// Just mark the whole block as used.
		*block &= ~MICROBIT_HEAP_BLOCK_FREE;
	}
	else
	{
		// We need to split the block.
		uint32_t *splitBlock = block + blocksNeeded;
		*splitBlock = blockSize - blocksNeeded;
		*splitBlock |= MICROBIT_HEAP_BLOCK_FREE;

		*block = blocksNeeded;
	}

	// Enable Interrupts
    __enable_irq();

	return block+1;
}

/**
  * Release a given area of memory from the heap.
  *
  * @param mem The memory area to release.
  */
void *microbit_malloc(size_t size)
{
    void *p;

    // Assign the memory from the first heap created that has space.
    for (int i=0; i < heap_count; i++)
    {
        p = microbit_malloc(size, heap[i]);
        if (p != NULL)
        {
#if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
            if(SERIAL_DEBUG) SERIAL_DEBUG->printf("microbit_malloc: ALLOCATED: %d [%p]\n", size, p);
#endif
            return p;
        }
    }

    // If we reach here, then either we have no memory available, or our heap spaces
    // haven't been initialised. Either way, we try the native allocator.

    p = native_malloc(size);
    if (p != NULL)
    {
#if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
        // Keep everything trasparent if we've not been initialised yet
        if (heap_count > 0)
            if(SERIAL_DEBUG) SERIAL_DEBUG->printf("microbit_malloc: NATIVE ALLOCATED: %d [%p]\n", size, p);
#endif
        return p;
    }

    // We're totally out of options (and memory!).
#if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
    // Keep everything transparent if we've not been initialised yet
    if (heap_count > 0)
        if(SERIAL_DEBUG) SERIAL_DEBUG->printf("microbit_malloc: OUT OF MEMORY [%d]\n", size);
#endif

#if CONFIG_ENABLED(MICROBIT_PANIC_HEAP_FULL)
	microbit_panic(MICROBIT_OOM);
#endif

    return NULL;
}

/**
  * Release a given area of memory from the heap.
  *
  * @param mem The memory area to release.
  */
void microbit_free(void *mem)
{
	uint32_t	*memory = (uint32_t *)mem;
	uint32_t	*cb = memory-1;

#if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
    if (heap_count > 0)
        if(SERIAL_DEBUG) SERIAL_DEBUG->printf("microbit_free:   %p\n", mem);
#endif
    // Sanity check.
	if (memory == NULL)
       return;

    // If this memory was created from a heap registered with us, free it.
    for (int i=0; i < heap_count; i++)
    {
        if(memory > heap[i].heap_start && memory < heap[i].heap_end)
        {
            // The memory block given is part of this heap, so we can simply
	        // flag that this memory area is now free, and we're done.
	        *cb |= MICROBIT_HEAP_BLOCK_FREE;
            return;
        }
    }

    // If we reach here, then the memory is not part of any registered heap.
    // Forward it to the native heap allocator, and let nature take its course...
    native_free(mem);
}