"A hidden (and hardware password protected, by means of required special values in processor registers) debug mode has been found in AMD processors, and documented by a reverse engineer called Czernobyl on the RCE Forums community today. It enables powerful hardware debugging features long longed for by reverse engineers, such as hardware data-aware conditional breakpoints, and direct hardware 'page guard'-style breakpoints. And the best part is, it's sitting right there in your processor already, just read the details and off you go with the debugging ninja powers!"
News:
http://hardware.slashdot.org/story/10/11/12/047243/Hidden-Debug-Mode-Found-In-AMD-ProcessorsSource:
http://www.woodmann.com/collaborative/knowledge/index.php/Super-secret_debug_capabilities_of_AMD_processors_!