Compiling run-time parametrisable designs

This paper explores representations and compilation of run-time parametrisable FPGA designs. We develop methods to produce designs with many run-time parameters, which would otherwise require an impractical number of bitstreams to be generated at compile time. Run-time parametrisation facilitates specialisation, which can be used to remove logic to produce a smaller and faster design. Our approach involves a source description based on Structural VHDL that allows designers to specify what parameters are available at compile time and at run time. Using this approach, converting a compile-time parameter into a run-time parameter or vice versa is straightforward. The source description does not contain explicit information on how to modify the design at run time. We describe a compilation scheme that can be used to extract this information, generate a run-time representation of the design and rapidly instantiate this representation at run time. We present techniques that allow a parametrised design to be incrementally modified in order to minimise the reconfiguration overhead Our compiler implementation generates a Java program that uses the JBits AN to implement the runtime representation and functions to incrementally modify the design. DES and AES encryption designs are used to illustrate our approach.