Building a new Software Defined Radio (SDR) system requires multidisciplinary research covering the engineering disciplines of communication systems, radio frequency, digital and analog hardware, software and digital signal processing. This paper focuses on the efforts at the low-level software development, such as device drivers, embedded source code at firmware-space and Application- Programming Interfaces (APIs) at user-space. In the early stages of constructing a SDR platform, design decisions are made regarding the interface between the SDR hardware and the PC. These decisions are of great importance and will determine the complexity of the low-level software development, its interoperability with third-party tools for waveform development and its efficiency in terms of bandwidth and configurability. This position paper reviews the experiences in using a USB interface between the PC and the SDR platform and the corresponding impact in the software development stage.