This work-in-progress paper introduces a new hardware platform for wireless sensor networks, summarizes the new challenges it creates for software development and describes a toolchain being developed to meet those challenges. The hardware platform is based on a low-power FPGA as opposed
to a traditional microcontroller. The FPGA configuration includes a soft core microcontroller, but there are plenty of resources left to implement a subset of the operating system, middleware and application components directly on the FPGA. Instead of creating this partition early in the design phase, we advocate a flexible hardware/software boundary enabling "late binding" of components to the softcore or the hardware fabric. This increases the complexity of the design space mandating sophisticated tool support. The paper describes a toolchain that helps manage this complexity. The two main tools are a domain-specic modeling environment and a symbolic design-space exploration tool.