Atmel CAVR-4 Manual De Usuario

CAVR-4

Part 1. Using the compiler

●

 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

●

Pointers with function memory attributes have restrictions in implicit and 
explicit casts between pointers and between pointers and integer types. For 
details about the restrictions, see Casting, page 142

●

-v2

 and 

-v4

: There are currently no derivatives that match these processor 

options, which have been added to support future derivatives

●

All implicit assumptions for a given 

-v

 option are also true for corresponding 

--cpu

 options.

It is important to be aware of the fact that the 

-v

 option does not reflect the amount of 

used data, but the maximum amount of addressable data. This means that, for example, 
if you are using a microcontroller with 16 Mbyte addressable data, but you are not using 
more than 256 bytes or 64 Kbytes of data, you must still use either the 

-v4

 or the 

-v6

 

option for 16 Mbyte data.

One of the characteristics of the AVR microcontroller is that there is a trade-off 
regarding the way memory is accessed, ranging from cheap access limited to small 
memory areas, up to more expensive access methods that can access any location in 
memory.

In the AVR IAR C/C++ Compiler, you can set a default memory access method by 
selecting a memory model. There are three memory models available—Tiny, Small, and 
Large. Your choice of processor option determines which memory models are available. 
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.

-v2

Tiny

_ _nearfunc

≤ 256 bytes

≤ 128 Kbytes

-v3

Tiny, Small

_ _nearfunc

≤ 64 Kbytes

≤ 128 Kbytes

-v4

Small, Large

_ _nearfunc

≤ 16 Mbytes

≤ 128 Kbytes

-v5

Tiny, Small

_ _farfunc

*

≤ 64 Kbytes

≤ 8 Mbytes

-v6

Small, Large

_ _farfunc

*

≤ 16 Mbytes

≤ 8 Mbytes