This paper proposes the use of formal feedback control theory as a way to implement adaptive techniques in the processor architecture. Dynamic thermal management (DTM) is used as a test vehicle, and variations of a PID controller (Proportional-Integral-Differential) are developed and tested for adaptive control of fetch "toggling." To accurately test the DTM mechanism being proposed, this paper also develops a thermal model based on lumped thermal resistances and thermal capacitances. This model is computationally efficient and tracks temperature at the granularity of individual functional blocks within the processor. Because localized heating occurs much faster than chip-wide heating, some parts of the processor are more likely, to be "hot spots" than others. Experiments using Wattch and the SPEC2000 benchmarks show that the thermal trigger threshold can be set within 0.2° of the maximum temperature and yet never enter thermal emergency. This cuts the performance loss of DTM by 65% compared to the previously described fetch toggling technique that uses a response of fixed magnitude.