Atmel CAVR-4 Manual De Usuario

CAVR-4

Descriptions of extended keywords

Reference Guide

_ _ext_io

Controls the storage of data objects in data memory space.

The 

_ _ext_io

 memory attribute implies that objects are 

_ _no_init

 and volatile, and 

allows objects to be accessed by use of the special I/O instructions in the AVR 
microcontroller.

Your application may access the AVR I/O system by using the memory-mapped internal 
special function registers (SFRs). To access the AVR I/O system efficiently, the 

_ _ext_io

 memory attribute should be included in the code.

_ _far

Controls the storage of data objects in data memory space.

The 

_ _far

 memory attribute overrides the default data storage of variables given by the 

selected memory model.

Note: When the 

_ _far

 memory attribute is used, the object cannot cross a 64-Kbyte 

boundary. Arithmetics will only be performed on the two lower bytes, except 
comparison which is always performed on the entire 24-bit address.

_ _farflash

Controls the storage of data objects in flash (code) memory space.

The 

_ _farflash

 memory attribute places objects in flash (code) memory.

Note that it is preferable to declare flash objects as 

const

. The 

_ _farflash

 memory 

attribute is only available for AVR chips with at least 64 Kbytes of flash memory.

The index type uses 16-bit arithmetic, which implies that a 64-Kbyte boundary cannot 
be crossed.

Note: When the 

_ _farflash

 memory attribute is used, the object cannot cross a 

64-Kbyte boundary. Arithmetics will only be performed on the two lower bytes, except 
comparison which is always performed on the entire 24-bit address.

0x100-0xFFFF

4 bytes (32 bits)

Pointers not allowed Data

0-0xFFFFFF

 (16 Mbytes)

65535 bytes

24 bits

Data

0-0x7FFFFF

 (8 Mbytes)

65535 bytes

24 bits

Code