Stephen Oualline - Bare Metal C: Embedded Programming for the Real World

This book is called Bare Metal C because its for people who get close to the hardware. Its not for people who buy their computer in a box and never see the inside. The computer used in this book doesnt even have a box. If you want to use it, youre going to have to connect something to the bare metal of the board.

This book teaches embedded programming. An embedded computer is one that sits inside the machine and you never know its there. Its the device that runs your garage door opener, your microwave, your car, or even your greeting card. But before it can do any of those things, it needs to be programmed. And that is what this book teaches you: how to program an embedded system.

Why C? C gives you precise control over what your program is doing, whereas other languages, such as C++, can do a great deal of things behind your back. Consider the following statement:

In C++, this could call a classs assignment operator function, which might result in heap memory being allocated and freed as well as an exception being thrown. What all that means is unimportant right now; the point is that you dont know exactly whats going to happen.

In C, this statement assigns the value b to the variable a with no side effects; its just an assignment, nothing more. This example is simple, but youll see other ways that C does exactly what you tell it throughout the book.

Precise control is important because we are using C to program a low-end system on a chip (SOC) system based on the STM32F030x4 processor (a cheap ARM Cortex-M0-based system) that has 8KB of RAM. Memory management is very important with limited RAM, so we cant afford to have a high-level language like C++ play with memory behind our backs. Precise control is also important because an embedded system doesnt have an operating system and you need to tell the hardware what to do directly. High-level languages dont always let you talk to the hardware, but C does.

The book is designed for people who have a basic knowledge of computers and hardware, but have a limited knowledge of programming. It is for the hardware designer who wants to connect a new piece of hardware to a microcontroller and use it for the first time. It is for the programmer who is interested in low-level programming and wants to get the most out of a 38 chip.

The ARM Cortex-M0 is very popular with low-end products because it costs 38 in quantities of 10,000 at the time of writing. Given that we hope to sell millions of whatever embedded system we are making, the difference between a 38 chip and a 56 chip is significant.

To get the most out of your programs, youll need to know what goes on under the hood. The book shows you not only how to write a program, but also how your program is translated into machine code thats used by the ARM chip. Thats important for maximum efficiency. For example, youll learn how much of a performance hit youll get if you change your program from using 16-bit integers to using 32-bit integers. The answer, surprisingly, is that 32-bit integers are more efficient and faster (32 bits is the natural number size for the ARM, and if its forced to do 16-bit arithmetic, it does 32-bit calculations and then throws away 16 bits).

To program and debug an ARM chip, youll need some extra tools: a flash memory programmer (to get your code into the machine), a USB-to-serial converter (because we use the serial line for debugging), and a JTAG debugger. Since almost all developers need this combination of tools, STMicroelectronics makes a board that provides all the hardware youll need, called the NUCLEO-F030R8. As of this writing, a chip shortage has made some boards hard to find. See https://nostarch.com/bare-metal-c for alternate boards. Youll also need a mini USB cable (the one that doesnt fit your phone) so you can plug the board into your computer.