Atmel CAVR-4 Manuale Utente

CAVR-4

Function storage

Reference Guide

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.

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 

_ _nearfunc

0-0x1FFFE

 (128 Kbytes) 16 bits

-v0

, -v1, -v2, -v3, -v4

_ _farfunc

0-0x7FFFFE

 (8 Mbytes)

24 bits

-v5

, -v6