Started following some tutorial on att85 usi. Downloaded example code from make avr book.

Make AVR Examples/AVR-Programming-Library/README.md

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+AVR-Programming-Library
+=======================
+
+Files that are re-used throughout the book *Make: AVR Programming*
+
+* **pinDefines.h**
+	Includes all of the pin definitions for the projects in *Make: AVR Programming*.  When you
+	need to know what to hook up where, have a look here.
+
+* **USART.c** and **USART.h**
+	These are the main utility files used for serial input/output in the book.  They're not
+	particularly clever, but they have a tiny memory and resource footprint and get you
+	up and running very quickly.
+
+* **binaryMacro.h**
+	If you're using a compiler other than a recent AVR-GCC, it may not support
+	native binary digits (e.g. 0b00111010).  If so, this include file has a pre-processor
+	macro that will let you enter them similarly: B8(01010101).  
+
+* **macros.h**
+	This file includes pre-processor macro definitions for bit-twiddling: 
+	set_bit, clear_bit, and toggle_bit.  Useful for those days when you're feeling
+	lazy, or have forgotten your bit-wise logic operations.
+
+* **portpins.h**
+	This is a recent version of the portpins.h file included with the Arduino environment.
+	It includes the AVR pin definitions of the form PB1 and similar.  The version included
+	with Arduino is very old -- you'll want to replace it with this one if you want to write
+	in C using the Arduino IDE. Or you can include this file directly in your code.
+