Specifications

CAVR-4

Function storage

AVR® IAR C/C++ Compiler

Reference Guide

Syntax

The extended keywords are specified before the return type, for example:

__interrupt void alpha(void);

The keywords that are type attributes must be specified both when they are defined and

in the declaration. Object attributes only have to be specified when they are defined

since they do not affect the way an object or function is used.

In addition to the rules presented here—to place the keyword directly in the code—the

directives #pragma type_attribute and #pragma object_attribute can be used

for specifying the keywords. Refer to the chapter Pragma directives for details about

how to use the extended keywords together with pragma directives.

Function storage

There are two memory attributes for controlling function storage:__nearfunc and

__farfunc

The following table summarizes the characteristics for each memory attribute:

When using the -v5 or the -v6 option, it is possible, for individual functions, to override

the __farfunc attribute and instead use the __nearfunc attribute. The default

memory attribute can be overridden by explicitly specifying a memory attribute in the

function declaration or by using the

#pragma type_attribute directive:

#pragma type_attribute=__nearfunc

void MyFunc(int i)

{

...

}

It is possible to call a __nearfunc function from a __farfunc function and vice versa.

Only the size of the function pointer is affected. Note that pointers with function

memory attributes have restrictions in implicit and explicit casts when casting between

pointers and also when casting between pointers and integer types; see Casting, page

142. For more information about function pointers, see Function pointers, page 141.

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

@ operator or the

#pragma location directive. For more information, see Controlling data and function

placement, page 47.

Memory attribute Address range Pointer size Used in processor option

__nearfunc 0-0x1FFFE (128 Kbytes) 16 bits -v0, -v1, -v2, -v3, -v4

__farfunc 0-0x7FFFFE (8 Mbytes) 24 bits -v5, -v6

Table 8: Memory attributes for functions