Atmel CAVR-4 Manual De Usuario

CAVR-4

Code segments

Reference Guide

A variable that has been explicitly placed at an address, for example by using the 
compiler 

@

 syntax, will be placed in either the 

SEGMENT_AC

 or the 

SEGMENT_AN

 

segment. The former is used for constant-initialized data, and the latter for items 
declared as 

_ _no_init

. The individual segment part of the segment knows its location 

in the memory space, and it should not be specified in the linker command file.

If you create your own data segments—see Controlling data and function placement, 
page 47—these must also be defined in the linker command file using the 

-Z

 or 

-P

 

segment control directives.

This section contains examples and descriptions of the segments used for storing code, 
in other words, functions, and the interrupt vector table. Typically, these segments are 
placed in the code memory space (flash).

The 

-Z

 command is used for defining all segments in the following examples. The 

addresses used in the examples are based on the assumed target system described in the 
Table 10, Memory layout of a target system (example), on page 35. Note that because 
the described target system is limited in size of code memory space, several segments 
supported by the compiler are not applicable for this target system.

For a complete list of all segments, see Summary of segments, page 149.

The interrupt vector table contains pointers to interrupt routines, including the reset 
routine. The table is placed in the segment 

INTVEC

. The AT90S80515 derivative has 13 

interrupt vectors and one reset vector. For this reason, you should specify 14 interrupt 
vectors, each of two bytes. 

The linker directive would then look like this:

-Z(CODE)INTVEC=0-1B /* 14 interrupt vectors; 2 bytes each */

Functions are placed in the 

CODE

 or 

FARCODE

 segments, depending on which 

-v

 

processor option you are using. The 

-v

 option implicitly determines the default function 

memory attributes 

_ _nearfunc

 or 

_ _farfunc

, which in turn determines the used 

segments for the functions. For information about which attribute is used by default for 
each 

-v

 option, see the Table 3, Summary of processor configuration, on page 8.