Looks like some hardware enthusiasts have worked out a method to enable debug mode within AMD processors. The original site isnâ€™t loading for us, but the text has been mirrored in this comment. Getting the chip into debug mode requires access passwords on four control registers. Weâ€™ve read through the writeup and it means very little to us but we didnâ€™t pull out a datasheet to help make sense of the registers being manipulated. It shouldnâ€™t be hard to find an old AMD system to try this out on. Weâ€™d love to hear about anything you do with this debug system.
Source: http://hackaday.com/2010/11/13/debug-mo ... amd-chips/Now that's quite extra-ordinary! I wonder if its possible to access something like that on more processors?