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Embedded Software Development
2.2.5 Application startup
In most embedded systems, an initialization sequence executes to set up the system
before the main task is executed.
Figure 2-5 shows the default initialization sequence.
Image
entry point
__main
C Library
USER CODE
.
__scatterload
copy/decompress RW data
copy non-root code
zero uninitialized data
.
.
.
__rt_entry
set up application stack
and heap
initialize library functions
call top-level
constructors (C++)
Exit from application
.
main()
causes the linker to
link in library
initialization code
Figure 2-5 Default initialization sequence
At a high level, the initialization sequence can be divided into three functional blocks.
__main branches directly to __scatterload. __scatterload is responsible for setting the
runtime image memory map, whereas __rt_entry (runtime entry) is responsible for
initializing the C library.
__scatterload carries out code and data copying, decompression of RW data if
necessary, and zeroing of ZI data.
__scatterload branches to __rt_entry. This sets up the application stack and heap,
initializes library functions and their static data, and calls any constructors of globally
declared objects (C++ only).
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