Atmel CAVR-4 Manual De Usuario

CAVR-4

Part1. Using the compiler

You can customize:

●

The functions related to character-based I/O

●

The formatters used by 

printf

/

sprintf

 and 

scanf

/

sscanf

.

The functions 

putchar

 and 

getchar

 are the fundamental functions through which C 

performs all character-based I/O. For any character-based I/O to be available, you must 
provide definitions for these two functions, using whatever facilities the hardware 
environment provides.

The creation of new I/O routines is based on the following files:

●

putchar.c

, which serves as the low-level part of functions such as 

printf

 

●

getchar.c

, which serves as the low-level part of functions such as 

scanf

. 

The code example below shows how memory-mapped I/O could be used to write to a 
memory-mapped I/O device:

_ _no_init volatile unsigned char DEV_IO @ address;

  int putchar(int outchar)

  {

    DEV_IO = outchar;

    return outchar;

  }

The exact address is a design decision. For example, it can depend on the selected 
processor variant.

For information about how to include your own modified version of 

putchar

 and 

getchar

 in your project build process, see Overriding library modules, page 61.

The 

printf

 and 

sprintf

 functions use a common formatter, called 

_formatted_write

. The full version of 

_formatted_write

 is very large, and 

provides facilities not required in many embedded applications. To reduce the memory 
consumption, two smaller, alternative versions are also provided in the standard C 
library.