Datasheet

The C and C++ Libraries
ARM DUI 0067D Copyright © 1999-2001 ARM Limited. All rights reserved. 4-57
4.8 Tailoring storage management
This section describes the functions from rt_heap.h that you can define if you are
tailoring memory management. There are also two helper functions that you can call
from your heap implementation.
See the
rt_heap.h and rt_memory.s include files for more information on
memory-related functions.
Note
Users who are developing embedded systems with limited RAM might require a system
that does not use the heap or any heap-using functions. Other users might require their
own heap functions. There are two library functions that can be included to cause a
warning message if the heap is used:
__use_no_heap()
Guards against use of
malloc() , realloc() , free() , and any function that
uses those (such as
calloc() and stdio ).
__use_no_heap_region()
Has the same properties as
__use_no_heap() , but in addition, guards
against other things that use the heap memory region. For example, if you
declare
main() as a function taking arguments, the heap region is used for
collecting
argc and argv .
4.8.1 Support for malloc
malloc() , realloc() , calloc() , and free() are built on a heap abstract data type. You can
either:
• Choose between Heap1 or Heap2, the two provided heap implementations.
• Write your own heap implementation of the abstract data type for heap. See
Creating your own storage-management system on page 4-60.
The default implementations of
malloc() , realloc() , and calloc() maintain an 8-byte
aligned heap.
Heap1: Standard heap implementation
Heap1, the default implementation, implements the smallest and simplest heap
manager. The heap is managed as a singly-linked list of free blocks held in increasing
address order. The allocation policy is first-fit by address.