Abstract-Software Defined Radios (SDR) offer great runtime flexibility both at the physical and MAC layer. This makes them an attractive platform for the development of cognitive radios that can adapt to changes in channel conditions, traffic load, and user requirements. However, to realize this goal, we need a software framework that supports both MAC protocol and PHY layer development in an integrated fashion. In this paper we report on our experience in using two different software frameworks for integrated PHY-MAC development for SDRs: GNU Radio, which was originally designed to support PHY layer development, and Click, a framework for protocol development. We also discuss a number of broader system considerations, such as what functionality should be offloaded to the SDR device.