My printf doesn't work

[Franzi Edo.]

Hi,
I would like to implement the "printf" function on my target.  
Accordingly with the documentation I found it seems that it should be  
enough to write some low level routine such "fstat, sbrk, istty, ...  
read, write". So, I implement these functions and I can monitor that  
fstat, sbrk and isatty are called during the printf. However, the  
"write" function is never called, and of course I cannot have the  
data out to my USART. Do I have initialise some I/O table or stuffs  
like this to make operational my printf? Any ideas?

I use gcc-4.1.0,
cpu32 target
newlib-1.14.0

Regards E. Franzi