RAPID PROTOTYPING OF HIGH PERFORMANCE SIGNAL PROCESSING APPLICATIONS

Abstract

Advances in embedded systems for digital signal processing (DSP) are enabling many scientific projects and commercial applications. At the same time, these applications are key to driving advances in many important kinds of computing platforms. In this region of high performance DSP, rapid prototyping is critical for faster time-to-market (e.g., in the wireless communications industry) or time-to-science (e.g., in radio astronomy). DSP system architectures have evolved from being based on application specific integrated circuits (ASICs) to incorporate reconfigurable off-the-shelf field programmable gate arrays (FPGAs), the latest multiprocessors such as graphics processing units (GPUs), or heterogeneous combinations of such devices. We, thus, have a vast design space to explore based on performance trade-offs, and expanded by the multitude of possibilities for target platforms. In order to allow systematic design space exploration, and develop scalable and portable prototypes, model based design tools are increasingly used in design and implementation of embedded systems. These tools allow scalable high-level representations, model based semantics for analysis and optimization, and portable implementations that can be verified at higher levels of abstractions and targeted toward multiple platforms for implementation. The designer can experiment using such tools at an early stage in the design cycle, and employ the latest hardware at later stages. In this thesis, we have focused on dataflow-based approaches for rapid DSP system prototyping. This thesis contributes to various aspects of dataflow-based design flows and tools as follows:

We have introduced the concept of topological patterns, which exploits commonly found repetitive patterns in DSP algorithms to allow scalable, concise, and parameterizable representations of large scale dataflow graphs in high-level languages. We have shown how an underlying design tool can systematically exploit a high-level application specification consisting of topological patterns in various aspects of the design flow.

We have formulated the core functional dataflow (CFDF) model of computation, which can be used to model a wide variety of deterministic dynamic dataflow behaviors. We have also presented key features of the CFDF model and tools based on these features. These tools provide support for heterogeneous dataflow behaviors, an intuitive and common framework for functional specification, support for functional simulation, portability from several existing dataflow

models to CFDF, integrated emphasis on minimally-restricted specification of actor functionality, and support for efficient static, quasi-static, and dynamic scheduling techniques.

We have developed a generalized scheduling technique for CFDF graphs based on decomposition of a CFDF graph into static graphs that interact at run-time. Furthermore, we have refined this generalized scheduling technique using a new notion of "mode grouping," which better exposes the underlying static behavior. We have also developed a scheduling technique for a class of dynamic applications that generates parameterized looped schedules (PLSs), which can handle dynamic dataflow behavior without major limitations on compile-time predictability.

We have demonstrated the use of dataflow-based approaches for design and implementation of radio astronomy DSP systems using an application example of a tunable digital downconverter (TDD) for spectrometers. Design and implementation of this module has been an integral part of this thesis work. This thesis demonstrates a design flow that consists of a high-level software prototype, analysis, and simulation using the dataflow interchange format (DIF) tool, and integration of this design with the existing tool flow for the target implementation on an FPGA platform, called interconnect break-out board (IBOB). We have also explored the trade-off between low hardware cost for fixed configurations of digital downconverters and flexibility offered by TDD designs.

This thesis has contributed significantly to the development and release of the latest version of a graph package oriented toward models of computation (MoCGraph). Our enhancements to this package include support for tree data structures, and generalized schedule trees (GSTs), which provide a useful data structure for a wide variety of schedule representations. Our extensions to the MoCGraph package provided key support for the CFDF model, and functional simulation capabilities in the DIF package.