Atmel CAVR-4 ユーザーズマニュアル

CAVR-4

Memory types and memory attributes

Reference Guide

Your project can only use one memory model at a time, and the same model must be 
used by all user modules and all library modules. If you do not specify a memory model 
option, the compiler will use the Tiny memory model for all processor options, except 
for 

-v4

 and 

-v6

, where the Small memory model will be used.

The following table summarizes the different memory models:

See the AVR® IAR Embedded Workbench™ IDE User Guide for information about 
setting options in IAR Embedded Workbench.

Use the 

--memory_model

 option to specify the memory model for your project; see -m, 

Note that the default memory type can be overridden by explicitly specifying a memory 
attribute, using either keywords or the 

#pragma type_attribute

 directive. For more 

information about the different memory types, see Memory types and memory 
attributes, page 18.

This section describes the concept of memory types used for accessing data by the AVR 
IAR C/C++ Compiler. It also discusses pointers in the presence of multiple memory 
types. For each memory type, the capabilities and limitations are discussed.

The AVR IAR C/C++ Compiler uses different memory types to access data that is 
placed in different areas of the memory. There are different methods for reaching 
memory areas, and they have different costs when it comes to code space, execution 
speed, and register usage. The access methods range from generic but expensive 
methods that can access the full memory range, to cheap methods that can access limited 
memory areas. Each memory type corresponds to one memory access method. By 
mapping different memories—or part of memories—to memory types, the compiler can 
generate code that can access data efficiently.

For example, the memory accessible using the near memory access method is called 
memory of near type, or simply near memory. 

Tiny

_ _tiny

_ _tiny

≤ 256 bytes

-v0

, -v1, -v2, -v3, -v5

Small

_ _near

_ _near

≤ 64 Kbytes

-v1

, -v3, -v4, -v5, -v6

Large

_ _far

_ _far

≤ 16 Mbytes

-v4

, -v6