RealView Compilation Tools Developer Guide - ARM Information ...

Embedded Software Development
2.4.6 Placing the stack and heap
Scatter-loading provides a method for specifying the placement of code and statically
allocated data in your image. The application stack and heap are set up during C library
initialization. You can tailor stack and heap placement by re-implementing the
__user_initial_stackheap() function. Alternatively you can use the specially named
ARM_LIB_HEAP and ARM_LIB_STACK execution regions. See Specifying stack and heap using
the scatter-loading description file on page 5-3 in the Linker and Utilities Guide for
more information.
2.4.7 Runtime memory models
Two runtime memory models are provided. In both runtime memory models, the stack
grows unchecked.
Note
Both these examples are suitable for the Integrator system.
One-region model
In the default, one-region model, the application stack and heap grow towards each
other in the same region of memory. In this case, the heap is checked against the value
of the stack pointer when new heap space is allocated, for example, when malloc() is
called.
Figure 2-9 on page 2-21 and Example 2-5 on page 2-21 show an example of
__user_initial_stackheap() implementing a simple one-region model, where the stack
grows downwards from address 0x40000, and the heap grows upwards from 0x20000.
The routine loads the appropriate values into the registers r0 and r1, and then returns.
Register r2 remains unchanged, because a heap limit is not used in a one-region model.
Register r3 is not used.
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