Atmel CAVR-4 사용자 설명서

CAVR-4

Part 1. Using the compiler

_ _no_init int alpha @ "MYSEGMENT"; /* OK */

#pragma location="MYSEGMENT"

const int beta=5;

/* OK */

const int gamma @ "MYSEGMENT" = 3;

/* OK */

int delta @ "MYSEGMENT";

/* Error, neither */

/* "_ _no_init" nor "const" */

It is possible to place functions into named segments using either the 

@

 operator or the 

#pragma

 

location

 directive. When placing functions into segments, the segment is 

specified as a string literal.

void f(void) @ "MYSEGMENT";

void g(void) @ "MYSEGMENT"

{

}

#pragma location="MYSEGMENT"

void h(void);

Using IAR extensions in C, read-only SFRs—for instance, in header files—can be 
declared like this:

volatile const _ _no_init int x @ 0x100;

In C++, 

const

 variables are static (module local), which means that each module with 

this declaration will contain a separate variable. When you link an application with 
several such modules, the linker will report that there are more than one variable located 
at address 

0x100

.

To avoid this problem and have it work the same way in C and C++, you should declare 
these SFRs 

extern

, for example:

extern volatile const _ _no_init int x @ 0x100;

In addition to the predefined segments, you can use your own segments. This is useful 
if you need to have precise control of placement of individual variables or functions.