In the time varying channel there is a requirement for the communication system to vary its function to adapt to the changing transmission conditions. The need for greater transmission capacity puts increasing demand on the processing requirements of such systems. This paper describes the concept of reconfigurable digital processing and highlights some of the problems encountered while designing such systems. An example of a reconfigurable channel coding algorithm is presented which illustrates the difficulty of designing reconfigurable systems particularly for adaptable communications systems such as those used for HF communication. This example illustrates the use of reconfigurable systems based around Golay and Hamming codes which are commonly used in HF systems. A design methodology is presented with software and hardware tools to enable the reconfigurable processing designer to easily design a reconfigurable digital processing system for communication in a time varying environment.