Atmel CAVR-4 Manual De Usuario

CAVR-4

Customizing system initialization

Reference Guide

If your project is linked with the XLINK options With runtime control modules or 
With I/O emulation modules, the normal 

_ _exit

 and 

abort

 functions are replaced 

with special ones. C-SPY will then recognize when those functions are called and can 
take appropriate actions to simulate program termination. For more information, see 
C-SPY Debugger runtime interface, page 76.

It is likely that you need to customize the code for system initialization. For example, 
your application might need to initialize memory-mapped special function registers 
(SFRs), or omit the default initialization of data segments performed by 

cstartup

.

You can do this by providing a customized version of the routine 

_ _low_level_init

, 

which is called from 

cmain

 before the data segments are initialized. Modifying the file 

cstartup

 directly should be avoided.

The code for handling system startup is located in the source files 

cstartup.s90

 and 

low_level_init.c

, located in the 

avr\src

 directory. 

Note: Normally, there is no need for customizing either of the files 

cmain.s90

 or 

cexit.s90

.

If you intend to rebuild the library, the source files are available in the template library 
project, see Building and using a customized library, page 62. 

Note: Regardless of whether you modify the routine 

_ _low_level_init

 or the file 

cstartup.s90

, you do not have to rebuild the library.

Some applications may need to initialize I/O registers, omit the default initialization of 
data segments performed by the system startup code, or set up for use of external 
memory.

You can do this by providing a customized version of the routine 

_ _low_level_init

, 

which is called from the system startup code before the data segments are initialized.

The value returned by 

_ _low_level_init

 determines whether or not data segments 

should be initialized by the system startup code. If the function returns 

0

, the data 

segments will not be initialized.

Note: The file 

intrinsics.h

 must be included by 

low_level_init.c

 to assure 

correct behavior of the 

_ _low_level_init

 routine.