In message 015101c427e1$b7b45470$6b01a8c0@cc you wrote:

I think that's not really important for you, but I really don't know where printf() function is declared in u-boot 1.0.0?

See include/common.h

I see everywhere that printf is called in many and many functions, but I really don't know how the string is sent through the debug serial port?

Anybody can tell how does it work?

The same question for input function like getc...

Please learn to use tools. Start with "man grep".

Best regards,

Wolfgang Denk