/* Copyright (c) 2007  Eric B. Weddington
   All rights reserved.

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are met:

   * Redistributions of source code must retain the above copyright
     notice, this list of conditions and the following disclaimer.
   * Redistributions in binary form must reproduce the above copyright
     notice, this list of conditions and the following disclaimer in
     the documentation and/or other materials provided with the
     distribution.
   * Neither the name of the copyright holders nor the names of
     contributors may be used to endorse or promote products derived
     from this software without specific prior written permission.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  POSSIBILITY OF SUCH DAMAGE. */

/* $Id: overview.dox 2510 2016-02-08 16:08:08Z joerg_wunsch $ */

/** 

\page overview Toolchain Overview

\section overview_introduction Introduction

Welcome to the open source software development toolset for the Atmel AVR!

There is not a single tool that provides everything needed to develop software
for the AVR. It takes many tools working together. Collectively, the group of
tools are called a toolset, or commonly a toolchain, as the tools are chained
together to produce the final executable application for the AVR 
microcontroller.

The following sections provide an overview of all of these tools. You may be
used to cross-compilers that provide everything with a GUI front-end, and not
know what goes on "underneath the hood". You may be coming from a desktop or
server computer background and not used to embedded systems. Or you may be
just learning about the most common software development toolchain available
on Unix and Linux systems. Hopefully the following overview will be helpful
in putting everything in perspective.


\section overview_fsf_and_gnu FSF and GNU

According to its website, "the Free Software Foundation (FSF), established in 
1985, is dedicated to promoting computer users' rights to use, study, copy, 
modify, and redistribute computer programs. The FSF promotes the development 
and use of free software, particularly the GNU operating system, used widely in 
its GNU/Linux variant." The FSF remains the primary sponsor of the GNU project.

The GNU Project was launched in 1984 to develop a complete Unix-like operating 
system which is free software: the GNU system. GNU is a recursive acronym for 
»GNU's Not Unix«; it is pronounced guh-noo, approximately like canoe.

One of the main projects of the GNU system is the GNU Compiler Collection, or
GCC, and its sister project, GNU Binutils. These two open source projects 
provide a foundation for a software development toolchain. Note that these 
projects were designed to originally run on Unix-like systems.


\section overview_gcc GCC

GCC stands for GNU Compiler Collection. GCC is highly flexible compiler system. 
It has different compiler front-ends for different languages. It has many
back-ends that generate assembly code for many different processors and host
operating systems. All share a common "middle-end", containing the generic 
parts of the compiler, including a lot of optimizations.

In GCC, a \e host system is the system (processor/OS) that the compiler
runs on. A \e target system is the system that the compiler compiles code for.
And, a \e build system is the system that the compiler is built (from source code) 
on. If a compiler has the same system for \e host and for \e target, it is
known as a \e native compiler. If a compiler has different systems for \e host
and \e target, it is known as a cross-compiler. (And if all three, \e build,
\e host, and \e target systems are different, it is known as a Canadian cross
compiler, but we won't discuss that here.) When GCC is built to execute on a 
\e host system such as FreeBSD, Linux, or Windows, and it is built to generate
code for the AVR microcontroller \e target, then it is a cross compiler, and
this version of GCC is commonly known as "AVR GCC". In documentation, or
discussion, AVR GCC is used when referring to GCC targeting specifically the
AVR, or something that is AVR specific about GCC. The term "GCC" is usually
used to refer to something generic about GCC, or about GCC as a whole.

GCC is different from most other compilers. GCC focuses on translating a
high-level language to the target assembly only. AVR GCC has three available
compilers for the AVR: C language, C++, and Ada. The compiler itself does not 
assemble or link the final code.

GCC is also known as a "driver" program, in that it knows about, and drives
other programs seamlessly to create the final output. The assembler, and the
linker are part of another open source project called GNU Binutils. GCC knows
how to drive the GNU assembler (gas) to assemble the output of the compiler.
GCC knows how to drive the GNU linker (ld) to link all of the object modules
into a final executable.

The two projects, GCC and Binutils, are very much interrelated and many of the
same volunteers work on both open source projects.

When GCC is built for the AVR target, the actual program names are prefixed
with "avr-". So the actual executable name for AVR GCC is: avr-gcc. The
name "avr-gcc" is used in documentation and discussion when referring to the
program itself and not just the whole AVR GCC system.

See the GCC Web Site and GCC User Manual for more information about GCC.


\section overview_binutils GNU Binutils

The name GNU Binutils stands for "Binary Utilities". It contains the GNU 
assembler (gas), and the GNU linker (ld), but also contains many other utilities
that work with binary files that are created as part of the software 
development toolchain.

Again, when these tools are built for the AVR target, the actual program names
are prefixed with "avr-". For example, the assembler program name, for a native
assembler is "as" (even though in documentation the GNU assembler is commonly
referred to as "gas"). But when built for an AVR target, it becomes "avr-as".
Below is a list of the programs that are included in Binutils:

\par avr-as
The Assembler.

\par avr-ld
The Linker.

\par avr-ar
Create, modify, and extract from libraries (archives).

\par avr-ranlib
Generate index to library (archive) contents.

\par avr-objcopy
Copy and translate object files to different formats.

\par avr-objdump
Display information from object files including disassembly.

\par avr-size
List section sizes and total size.

\par avr-nm
List symbols from object files.

\par avr-strings
List printable strings from files.

\par avr-strip
Discard symbols from files.

\par avr-readelf
Display the contents of ELF format files.

\par avr-addr2line
Convert addresses to file and line.

\par avr-c++filt
Filter to demangle encoded C++ symbols.


\section overview_avr-libc avr-libc

GCC and Binutils provides a lot of the tools to develop software, but there is
one critical component that they do not provide: a Standard C Library.

There are different open source projects that provide a Standard C Library
depending upon your system time, whether for a native compiler (GNU Libc),
for some other embedded system (newlib), or for some versions of Linux (uCLibc). 
The open source AVR toolchain has its own Standard C Library project: avr-libc.

AVR-Libc provides many of the same functions found in a regular Standard C
Library and many additional library functions that is specific to an AVR. Some
of the Standard C Library functions that are commonly used on a PC environment
have limitations or additional issues that a user needs to be aware of when 
used on an embedded system.

AVR-Libc also contains the most documentation about the whole AVR toolchain.


\section overview_building_software Building Software

Even though GCC, Binutils, and avr-libc are the core projects that are used
to build software for the AVR, there is another piece of software that
ties it all together: Make. GNU Make is a program that makes things, and 
mainly software. Make interprets and executes a Makefile that is written
for a project. A Makefile contains dependency rules, showing which 
output files are dependent upon which input files, and instructions on how
to build output files from input files.

Some distributions of the toolchains, and other AVR tools such as MFile, 
contain a Makefile template written for the AVR toolchain and AVR applications
that you can copy and modify for your application.

See the GNU Make User Manual for more information.


\section overview_avrdude AVRDUDE

After creating your software, you'll want to program your device. You can do
this by using the program AVRDUDE which can interface with various hardware 
devices to program your processor.

AVRDUDE is a very flexible package. All the information about AVR processors
and various hardware programmers is stored in a text database. This database
can be modified by any user to add new hardware or to add an AVR processor
if it is not already listed.


\section overview_gdb_insight_ddd GDB / Insight / DDD

The GNU Debugger (GDB) is a command-line debugger that can be used with
the rest of the AVR toolchain. Insight is GDB plus a GUI written in Tcl/Tk. 
Both GDB and Insight are configured for the AVR and the main executables are 
prefixed with the target name: avr-gdb, and avr-insight. 
There is also a "text mode" GUI for GDB: avr-gdbtui. DDD (Data Display Debugger) 
is another popular GUI front end to GDB, available on Unix and Linux systems.


\section overview_avarice AVaRICE

AVaRICE is a back-end program to AVR GDB and interfaces to the Atmel JTAG
In-Circuit Emulator (ICE), to provide emulation capabilities.


\section overview_simulavr SimulAVR

SimulAVR is an AVR simulator used as a back-end with AVR GDB.


\section overview_utilities Utilities

There are also other optional utilities available that may be useful to add
to your toolset. 

\c SRecord is a collection of powerful tools for manipulating 
EPROM load files. It reads and writes numerous EPROM file formats, and can 
perform many different manipulations.

\c MFile is a simple Makefile generator is meant as an aid to quickly customize 
a Makefile to use for your AVR application.


\section overview_distros Toolchain Distributions (Distros)

All of the various open source projects that comprise the entire toolchain
are normally distributed as source code. It is left up to the user to build
the tool application from its source code. This can be a very daunting task
to any potential user of these tools.

Luckily there are people who help out in this area. Volunteers take the time
to build the application from source code on particular host platforms and 
sometimes packaging the tools for convenient installation by the end user.
These packages contain the binary executables of the tools, pre-made and ready
to use. These packages are known as "distributions" of the AVR toolchain,
or by a more shortened name, "distros".

AVR toolchain distros are available on FreeBSD, Windows, Mac OS X, and
certain flavors of Linux.


\section overview_open_source Open Source

All of these tools, from the original source code in the multitude of projects, 
to the various distros, are put together by many, many volunteers. All of these
projects could always use more help from other people who are willing to 
volunteer some of their time. There are many different ways to help, for people
with varying skill levels, abilities, and available time.

You can help to answer questions in mailing lists such as the avr-gcc-list, or 
on forums at the AVR Freaks website. This helps many people new to the open 
source AVR tools.

If you think you found a bug in any of the tools, it is always a big help to
submit a good bug report to the proper project. A good bug report always
helps other volunteers to analyze the problem and to get it fixed for future
versions of the software.

You can also help to fix bugs in various software projects, or to add desirable
new features.

Volunteers are always welcome! :-)

*/
