As embedded systems continue to face increasingly higher performance requirements, deeply pipelined processor architectures are being employed to meet desired system performance. System architects critically need modeling techniques to rapidly explore and evaluate candidate architectures based on area, power, and performance constraints. We present an exploration framework for pipelined processors. We use the EXPRESSION Architecture Description Language (ADL) to capture a wide spectrum of processor architectures. The ADL has been used to enable performance driven exploration by generating a software toolkit from the ADL specification. In this paper, we present a functional abstraction technique to automatically generate synthesizable RTL from the ADL specification. Automatic generation of RTL enables rapid exploration of candidate architectures under given design constraints such as area, clock frequency, power, and performance. Our exploration results demonstrate the power of reuse in composing heterogeneous architectures using functional abstraction primitives allowing for a reduction in the time for specification and exploration by at least an order of magnitude.