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Embedded Software Development
2.5 Reset and initialization
This chapter has so far assumed that execution begins at __main, the entry point to the C
library initialization routine. In fact, any embedded application on your target hardware
performs some system-level initialization at startup. This section describes this in more
detail.
2.5.1 Initialization sequence
Figure 2-11 shows a possible initialization sequence for an embedded system based on
an ARM architecture.
__main
.
C Library
__scatterload
copy/decompress RW data
copy non-root code
zero uninitialized data
.
.
__rt_entry
3
4
initialize library
functions
call top-level
constructors (C++)
Exit from application
2
5
6
8
.
USER CODE
reset handler
initialize stack pointers
configure MMU/MPU
. setup cache/enable
TCM
.
__user_initial_stackheap()
set up application stack
and heap
.
$Sub$$main()
enable caches and
interrupts
.
main()
causes the linker to link
in library initialization
code
1
Image
entry point
7
Figure 2-11 Initialization sequence
The reset handler executes immediately on system startup. The block of code labeled
$Sub$$main() executes immediately before entering the main application.
The reset handler is a short module coded in assembler that is executed on system reset.
As a minimum, your reset handler initializes stack pointers for the modes that your
application is running in. For cores with local memory systems, such as caches, Tightly
Coupled Memories (TCMs), Memory Management Units (MMUs), and Memory
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