Improving functional density of time-critical applications using hardware-based dynamic reconfiguration and bitstream specialisation

The dynamic reconfiguration of an FPGA has many advantages, but the overhead from the process reduces the functional density of applications. Functional density is an indication of the composite benefits a reconfigured application obtains above its generic counterpart and measures the computational throughput per unit hardware resources. Typically, only quasi-static applications obtain a functional density advantage by dynamically reconfiguring its parameters. Contributing to the functional density reduction of applications with tight time constraints is the overhead to generate a new configuration, and the time it takes to load it onto the device. Normally these applications have to reuse their hardware numerous times between configurations before obtaining a functional density advantage. The most promising reconfiguration method to improve functional density with minimal hardware reuse was one that extracts certain characteristics from the bitstream and then implements a bitstream specialiser that generates new hardware at bit-level while the device is being reconfigured. While it was shown that this method allows reconfiguration of an application in real-time, its effect on functional density was not determined. This paper will show that a significant increase in functional density can be achieved for applications where reconfiguration is required before the next execution cycle of the application.