Turbo codes (TCs) have been proposed to reduce the required transmission energy in wireless sensor networks (WSNs), although this gain must be offset by the turbo decoder's processing energy consumption (EC). Previously, it has not been possible to estimate this processing EC until a relatively late stage in the TC design process. This has prevented the consideration of processing EC at the early design stages, when there is the greatest opportunity to adjust the parameters of the design. To address this, we propose a generalized turbo decoder architecture that supports a wide variety of parameters and a framework to estimate its EC as a function of these parameters at an early design stage. We demonstrate that this facilitates a holistic optimization of the TC parameters, minimizing the sum of both the transmission and processing EC.