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118 lines
3.9 KiB
118 lines
3.9 KiB
/**
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* A simple 32 bit block based memory allocator. This allows one or more memory segments to
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* be designated as heap storage, and is designed to run in a static memory area or inside the standard C
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* heap for use by the micro:bit runtime. This is required for several reasons:
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*
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* 1) It reduces memory fragmentation due to the high churn sometime placed on the heap
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* by ManagedTypes, fibers and user code. Underlying heap implentations are often have very simplistic
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* allocation pilicies and suffer from fragmentation in prolonged use - which can cause programs to
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* stop working after a period of time. The algorithm implemented here is simple, but highly tolerant to
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* large amounts of churn.
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*
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* 2) It allows us to reuse the 8K of SRAM set aside for SoftDevice as additional heap storage
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* when BLE is not in use.
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*
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* 3) It gives a simple example of how memory allocation works! :-)
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*
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* N.B. The need for this should be reviewed in the future, should a different memory allocator be
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* made availiable in the mbed platform.
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*
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* P.S. This is a very simple allocator, therefore not without its weaknesses. Why don't you consider
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* what these are, and consider the tradeoffs against simplicity...
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*
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* TODO: Consider caching recently freed blocks to improve allocation time.
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*/
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#ifndef MICROBIT_HEAP_ALLOCTOR_H
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#define MICROBIT_HEAP_ALLOCTOR_H
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#include "mbed.h"
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#include <new>
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// The number of heap segments created.
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#define MICROBIT_HEAP_COUNT 2
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// Flag to indicate that a given block is FREE/USED
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#define MICROBIT_HEAP_BLOCK_FREE 0x80000000
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/**
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* Initialise the microbit heap according to the parameters defined in MicroBitConfig.h
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* After this is called, any future calls to malloc, new, free or delete will use the new heap.
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* n.b. only code that #includes MicroBitHeapAllocator.h will use this heap. This includes all micro:bit runtime
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* code, and user code targetting the runtime. External code can choose to include this file, or
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* simply use the standard mbed heap.
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*
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* @return MICROBIT_OK on success, or MICROBIT_NO_RESOURCES if the heap could not be allocted.
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*/
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int microbit_heap_init();
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/**
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* Attempt to allocate a given amount of memory from any of our configured heap areas.
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* @param size The amount of memory, in bytes, to allocate.
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* @return A pointer to the allocated memory, or NULL if insufficient memory is available.
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*/
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void *microbit_malloc(size_t size);
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/**
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* Release a given area of memory from the heap.
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* @param mem The memory area to release.
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*/
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void microbit_free(void *mem);
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/*
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* Wrapper function to ensure we have an explicit handle on the heap allocator provided
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* by our underlying platform.
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*
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* @param size The amount of memory to allocate.
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* @return A pointer to the memory allocated. NULL if no memory is available.
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*/
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inline void *native_malloc(size_t size)
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{
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return malloc(size);
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}
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/*
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* Wrapper function to ensure we have an explicit handle on the heap allocator provided
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* by our underlying platform.
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*
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* @param p Pointer to the memory to be freed.
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*/
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inline void native_free(void *p)
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{
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free(p);
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}
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/**
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* Overrides the 'new' operator globally, and redirects calls to the micro:bit theap allocator.
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*/
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inline void* operator new(size_t size) throw(std::bad_alloc)
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{
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return microbit_malloc(size);
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}
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/**
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* Overrides the 'new' operator globally, and redirects calls to the micro:bit theap allocator.
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*/
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inline void* operator new[](size_t size) throw(std::bad_alloc)
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{
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return microbit_malloc(size);
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}
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/**
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* Overrides the 'delete' operator globally, and redirects calls to the micro:bit theap allocator.
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*/
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inline void operator delete(void *ptr) throw()
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{
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microbit_free(ptr);
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}
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// Macros to override overrides the 'malloc' and 'delete' functions globally, and redirects calls
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// to the micro:bit theap allocator.
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#define malloc(X) microbit_malloc( X )
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#define free(X) microbit_free( X )
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#endif
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