Wireless Sensor Networks (WSNs) have been deployed in a wide range of applications with different sensing and communication requirements. As a consequence, various MAC solutions have been proposed suiting to different application characteristics [1]. However, MAC protocols are typically implemented in a monolithic fashion -- specific to a particular hardware platform. This hinders the possibility of code re-use across different platforms, which makes both implementation and porting cumbersome. It also imposes difficulties in protocol redesign when the application requirements change since the entire radio stack needs to be modified.