Here you'll find all the code (and more!) for the Maker Media book Make: AVR Programming.
First, download the contents of this repository onto your hard-drive. The easiest way is with the "Download ZIP" button above and on the right-hand side of this very web page. Extract the zip file wherever is comfy. (Feel free to clone the repo if you are comfortable with Git.)
Most of the projects share a common set of pin defines and a common simple USART serial library in the AVR-Programming-Library directory. The makefiles I've included depend on the directory structure here by default, so don't go moving the folders around unless you also change the path to included files in the makefile.
If you're using the Arduino IDE, you'll want to copy the AVR-Programming-Library directory into your sketchbook/libraries folder. If you don't know where this is, you can find out in the "File...Settings" dialog within Arduino. Now you can link your code to use this library simply using "Sketch...Import Library" and selecting the library from the the menu.
Now you will be set to open the code, edit it, and flash it into the AVR following the directions in the book.
All of the project code is organized by the chapters in the book. So if you're looking for an example of some SPI code, see the "Chapter16_SPI" folder for SPI-related projects. That's obvious.
But a bunch of the projects are interesting in addition to the topic covered in the chapter. For instance, "Chapter05_Serial-IO" includes a project that uses the serial communication between your desktop computer and the AVR to turn your computer keyboard into a musical keyboard that plays notes generated on the AVR, turning it into a serial-port-controlled organ. You wouldn't think to go looking in the Serial I/O chapter unles you were following along in the book.
So for an overview all the projects, the file allProjectsList lists them all out by name.
If you'd like a blank template to start writing your own AVR code, have a look in the setupProject directory that I've included here. Inside, you'll find main.c and main.h files that are essentially blank and ready to go. main.c makes use of my simple USART library, which is also included an linked in by the Makefile. In short, you could copy this directory, rename files, and start using it in your own projects.
But you don't have to do that manually. Running python setupProject.py myProjectName will create a directory called myProjectName for you, copy the blank main files, renaming them as appropriate, and set up the Makefile accordingly. All that's left for you to do is the hard part -- actually coding.
If you use this setup a lot, you'll want to personalize the Makefile and the two main files to suit your own preferences. That way, whenever you start up a new project, it'll include a customized Makefile that has your programmer, chip type, and favorite baud rate already set.
Finally, if you like to map out your pin definitions in macro definitions, run python createPinDefines.py. The program will ask you what you'd like to call each pin macro (e.g. "LED0") and then which pin on the AVR you'd like to associate with it (e.g. "PB1"). When you're done entering your pin layout, it'll create a "pinDefines.h" file with (I hope) nicely-named macros. Move this file into the right directory, and include it in your code. Calling LED0_SET_HIGH will turn your LED on.
You've read the book, you've built the projects, you've worked through the code. But still you hunger for more projects, more examples, more, more, more! If I may toot my own horn, you should visit LittleHacks.org where I blog about whatever microcontroller projects I'm currently up to.
In particular, if you're reading Make: AVR Programming, and you're interested in fully-elaborated versions of the projects with more photos, videos, and explanation than could fit in a book, head on over to LittleHacks.org's AVR-Programming Section.
Once you've exhausted all of these resources, you should definitely head over to The Cornell University ECE 4760 Final Projects list page. It's an awe-inspiring collection of applications, and sure to spark some creative thoughts. It's all well-documented and there's tons of source code in C. [Professor Land's links section] (http://people.ece.cornell.edu/land/courses/ece4760/#links) is also top-notch, and his lectures on YouTube are also worth a look if you're getting serious about this whole AVR deal.