Welcome to module two. In this video, will be introducing the build system which is just a fancy way to describe the environment and the tools needed to compile a software project. In our Embedded System Development Platform, build system is contained on the host machine. The tools that will be using are provided by GNU's Compiler Collection or GCC for short. GNU bundles many useful compilation tools together, and we'll often refer to this as our toolchain. GCC was developed by a third party as free software, and most importantly, GCC supports a wide array of architectures including ARM. This wide support is important for developers who have a wish to have some flexibility in their platform choice. You may end up using many different architectures and many different compilers in your career. But the concept you will learn in this module will be extendable to other projects. The main job of the compiler toolset is to translate a high-level language into architecture specific languages. For this module, you will learn how to use the compiler toolchain on our host Linux virtual machine, or VM, to investigate the steps of compilation. With demos and assessment guidance you will set up your environment and get your tools installed to begin work on your own build system. By the end of the module you'll be able to design your own build environment. The architecture specific language we need to translate our C-Program into is called assembly. Assembly language does not directly get installed onto your processor. The assembly is translated into machine code, which is a binary encoding of assembly instructions. This machine code is what the processor understands and uses to perform work. The machine code binary representation, these encoded instructions, can be looked up in the processor's Instruction Set Architecture, or the ISA. Providing specific guidance and optimizations during the build process, is important for our embedded platform as the assembly instructions are the objects that need to be optimized before they are converted into the processor executable. Our toolchain for building a software project and installing it will include many applications of the GCC toolchain. You can refer to these general applications needed for the build toolchain as the preprocessor, the compiler, the assembler, the linker, the locator and the loader installer. The first five applications in the build and install process are the five steps for building a software project. The roles of these different build tools can be described very simply. The preprocessor will take your source files Cs and Hs and transform into new files by evaluating preprocessor directives and performing macro substitution. These modified files are then fed into the compiler proper. This performs a C programming to assembly code translation. Next, the assembler converts our assembly code into object code. Object code looks like confusing binary data and it's not really human readable. This assembly to object code conversion gets repeated from many source files. Now, object files need to be combined into a single executable where all references between object files need to be resolved. We call these references symbols. Now, this job is performed by the linker. Finally, the linker provides the linked file to a relocator where which will map all the addresses of code and data into the processor's memory space. The final file should be your target executable and all that needs to happen is to be installed on your target system. Embedded engineers are usually very involved with customizing each of these steps for their specific application. The operation of installing a build could be considered part of the build system, but we would be performing this with the help of other tools. For your project, you will use an IDE to help install an executable onto your system and I will address this in later modules. In general, you can think of compilation as converting source files into object code. These source files can be assembly or C programs. You can perform this translation as many steps as you like, but eventually, these files have to head into the linker. You should note that once you compile a project, the executable only work on the architecture you compiled at for. It cannot be run on other systems. Native compilation is when you compile your build for the same system you intend to run the executable on. Typically, we do not natively compile embedded projects as we use a host machine to compile our microcontroller software builds. When you compile an executable on one system and it is intended to run on another, this is referred to as cross compilation. We have to Cross Compiler microcontroller builds because the microcontroller itself does not usually have an operating system or the resources for programs like GCC to be installed for us to perform a build. More advanced machines may have this capability, like the Cortex-A ARM processor set, but we will not cover that in this course. Again, you remember that with our development platform, we may have an on board debugger that can help us with installing. This is not change how the Cross Compiler operate. And you gain more experience with writing software. You'll begin to design your own libraries for different objectives. And you may even find that some open source software can integrate into your project. Creating your own headers and including libraries will be an important part of development. And we'll have some major implications on how we set up our build environment. We will cover this process later in the module. Now, the GCC tool chain will not be the only GNU application that will help us during our software development. As you begin to learn the ins and outs of building, you will learn that building large software projects can be tedious. Managing the compilation of many files, with all their respective compile options becomes very cumbersome. To help with this, you'll be introduced to another useful tool in the GNU tool chain called Make. Make is a tool that controls the generation of executables and other non source files of a program from the program source files. Make will help us manage this whole process of building our executable. In each of the following videos, we will gain confidence using the GNU Toolchain to build our software product. Instead of installing on a target system, we will start first by learning to simulate our software on a host machine, and validate non architecture specific pieces before moving on to our intended target. Mastering how to use these build tools will prove immensely valuable in industry and in your own projects. So it's my commitment that by the end of this module you will be able to implement a build system using GNU's make and GCC compiler tool chain. Examine the pre-processors role in compilation, and integrate new libraries to a build system.
