Nuts and Volts - August 2008

by Joe Pardue

Get started now with this series! Joe’s book & kit are available in our webstore at

www.nutsvolts.com

PART 1:

Introducing the AVR C

Programming Workshop Series

Cprogramming and microcontrollers are two big topics, practically continental in size, and like continents, are easy to get lost in. Combining the two is a little like traipsing from Alaska to Tierra del Fuego. Chances are you’ll get totally lost and if the natives don’t eat you, your infected blisters will make you want to sit and pout. I’ve been down this road so many times that I probably have my own personal rut etched in the metaphorical soil, and I can point to the sharp rocks I’ve stepped on, the branches that have whacked me in the face, and the bushes from which the predators leapt. If you get the image of a raggedy bum stumbling through the jungle, you’ve got me right. Consider these workshops a combination roadmap, guidebook, and emergency first aid kit for your journey into this fascinating, but sometimes dangerous world.

I highly recommend that you get the book The C Programming Language — Second Edition by Kernighan and Ritchie, here after referred to as K&R. Dennis Ritchie (Figure 1) wrote C, and his book is the definitive source on all things C.

In Figure 1, Ritchie (inventor of the C programming language) stands next to Ken Thompson, original inventor of Unix, designing the original Unix operating system at Bell Labs on a PDP- 11.

I have chosen to follow that book’s organization structure in this series of workshops. The main

difference is that their book is machine independent and gives lots of examples based on manipulating text, while these workshops are machine dependent, specifically based on the AVR microcontroller, and the examples are as microcontroller oriented as I can make them.

Why C?

Back in the dark ages of microprocessors, software development was done exclusively in the specific assembly language of the specific device. These assembly languages were character based ‘mnemonic’ substitutions for the numerical machine language codes. Instead of writing something like: 0x12 0x07 0xA4 0x8F to get the device to load a value into a memory location, you could write something like: MOV 22, MYBUFFER+ 7. The assembler would translate that statement into the machine language for you.

I’ve written code in machine language (as a learning experiment) and believe me when I tell you that assembly language is a major step up in productivity. But a device’s assembly language is tied to the device and the way the device works. Assembly languages are hard to master and become obsolete for you the moment you change microcontroller families.

They are specific-purpose languages that work only on specific microprocessors. C is a general-purpose programming language that can work on any microprocessor that has a

C compiler written for it.

C abstracts the concepts of what a computer does and provides a text based logical and readable way to get computers to do what computers do. Once you learn C, you can move easily between microcontroller families, write software much faster, and create code that is much easier to understand and maintain.

Why AVR?

There are many excellent micro-controller families out there, but I chose the AVR because — among many reasons — it was designed with the C programming language in mind, has Flash memory that can be configured with a bootloader (more on all this later), and has the best user forum I’ve ever used: www.avr freaks.net.