In a microprocessor, a debug facility traps accesses to a peripheral device, such as a speaker, residing at I/O port addresses. In one embodiment, a number of debug registers are provided for a system or an application program to set a trap at specific I/O or memory address, and to associate...http://www.google.com.au/patents/US5680620?utm_source=gb-gplus-sharePatent US5680620 - System and method for detecting access to a peripheral device using a debug register 
