NAME

       overview - Toolchain Overview

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.

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.

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 host system is the system (processor/OS) that the compiler runs on. A target
       system is the system that the compiler compiles code for. And, a build system is the
       system that the compiler is built (from source code) on. If a compiler has the same system
       for host and for target, it is known as a native compiler. If a compiler has different
       systems for host and target, it is known as a cross-compiler. (And if all three, build,
       host, and 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 host system such as FreeBSD,
       Linux, or Windows, and it is built to generate code for the AVR microcontroller 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.

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:

       avr-as
           The Assembler.

       avr-ld
           The Linker.

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

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

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

       avr-objdump
           Display information from object files including disassembly.

       avr-size
           List section sizes and total size.

       avr-nm
           List symbols from object files.

       avr-strings
           List printable strings from files.

       avr-strip
           Discard symbols from files.

       avr-readelf
           Display the contents of ELF format files.

       avr-addr2line
           Convert addresses to file and line.

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

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.

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.

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.

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.

AVaRICE

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

SimulAVR

       SimulAVR is an AVR simulator used as a back-end with AVR GDB. Unfortunately, this project
       is currently unmaintained and could use some help.

Utilities

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

       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.

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

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.

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! :-)