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Arm Compiler User Guide : Reset and initialization

Reset and initialization

The entry point to the C library initialization routine is __main. However, an embedded application on your target hardware performs some system-level initialization at startup.

Embedded system initialization sequence

The following figure shows a possible initialization sequence for an embedded system based on an Arm® architecture:

Figure 7-9 Initialization sequence

If you use a scatter file to tailor stack and heap placement, the linker includes a version of the library heap and stack setup code using the linker defined symbols, ARM_LIB_*, for these region names. Alternatively you can create your own implementation.

The reset handler is normally a short module coded in assembler that executes immediately on system startup. As a minimum, your reset handler initializes stack pointers for the modes that your application is running in. For processors with local memory systems, such as caches, TCMs, MMUs, and MPUs, some configuration must be done at this stage in the initialization process. After executing, the reset handler typically branches to __main to begin the C library initialization sequence.

There are some components of system initialization, for example, the enabling of interrupts, that are generally performed after the C library initialization code has finished executing. The block of code labeled $Sub$$main() performs these tasks immediately before the main application begins executing.

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