We describe the motivation and design of a novel embedded systems architecture for large networks of small devices, tha canonical example being wireless sensor networks. The architecture differs from previous work in being based explicitly on a hardware/software co-design approach centred around the deployment of novel programming language constructs directly onto hardware in order to improve optimisation and expressibility. The programming interface enables the dynamic download and execution of domain-specific code to facilitate the development of context aware pervasive computing systems whose behaviour must adapt to their changing environment. To this end, the architecture implements a virtual machine operating environment based on Scheme and \uClinux~that encapsulates a CPU core, digital logic, generic I/O, network interfaces and domain-specific programming language composition. ; Paper presented to the 1st IFIP TC6 WG6.6 International Workshop on Autonomic Communication (WAC 2004), Berlin, 18-19 October, 2004.