When designing systems-on-a-chip (SoCs), a unique opportunity exists to generate custom FPGA architectures that are specific to the application domain in which the device will be used. The inclusion of such devices provides an efficient compromise between the flexibility of software and the performance of hardware, while at the same time allowing for post-fabrication modification of the SoC. To automate the layout of reconfigurable subsystems for systems-on-a-chip, we present the Circuit Generator Method. The Circuit Generator Method enables a designer to leverage the regularity that exists in FPGAs, creating structures that have only the needed resources to support the specified application domain. To facilitate this we have created generators that automatically produce the various components of the custom reconfigurable device. Compared to the unaltered full-custom tile, we achieve designs that are on average approximately 46% smaller and 16% faster, while continuing to support the ...