For an AVR microcontroller, the closest thing to a config file is its set of fuses. Fuses are used to configure important system parameters.

While you may completely ignore a number of the more esoteric options most of the time, you will undoubtedly need access to a few of these settings (such as the clock source fuse bits, which allow you to specify the source and/or speed of the chip clock) in the course of hacking AVRs.

You will need to know how to program these fuse bytes in order to get the most out of your microcontroller (or get it working at all!) and this simple tutorial will get you started right.

Link to Tutorial: http://electrons.psychogenic.com/modules/a...sHOWTOGuide.php