Experiences Teaching an FPGA-based Embedded Systems Class

I describe a two-year-old embedded systems design course I teach at Columbia University. In it, the students learn low-level C programming and VHDL coding to design and implement a project of their own choosing. The students implement their projects using Xilinx FPGAs and tools running on Linux workstations. The main challenges the students face are understanding and complying with complex and often poorly-documented interfaces and protocols, personal time management, and teamwork. While all real-world challenges, this class is often the first time the students encounter them, which makes the class quite challenging, but very practical. In this paper, I describe the structure of the class, the configuration of our teaching laboratory, some of the more successful projects, and give suggestions to instructors wishing to implement the class elsewhere

The Challenges of Hardware Synthesis from C-like Languages

The relentless increase in the complexity of integrated circuits we can fabricate imposes a continuing need for ways to describe complex hardware succinctly. Because of their ubiquity and flexibility, many have proposed to use the C and C++ languages as specification languages for digital hardware. Yet, tools based on this idea have seen little commercial interest. In this paper, I argue that C/C++ is a poor choice for specifying hardware for synthesis and suggest a set of criteria that the next successful hardware description language should have

The Challenge of Hardware Synthesis from C-like Languages

Many techniques for synthesizing digital hardware from C-like languages have been proposed, but none have emerged as successful as Verilog or VHDL for register-transfer-level design. Familiarity is the main reason C-like languages have been proposed for hardware synthesis. Synthesize hardware from C, proponents claim, and a C programmer can be turned into a hardware designer. Another common motivation is hardware/software codesign: today's systems usually contain a mix of hardware and software, and it is often unclear initially which portions to implement in hardware. Here, using a single language should simplify the migration task. The paper surveys several C-like hardware synthesis languages and looks at two of the fundamental challenges, concurrency and timing control

Design Languages for Embedded Systems

Embedded systems are application-specific computers that interact with the physical world. Each has a diverse set of tasks to perform, and although a very flexible language might be able to handle all of them, instead a variety of problem-domain-specific languages have evolved that are easier to write, analyze, and compile. This paper surveys some of the more important languages, introducing their central ideas quickly without going into detail. A small example of each is included

Using Program Specialization to Speed SystemC Fixed-Point Simulation

Generic simulation components, such as fixed-precision arithmetic routines, make it easier to quickly assemble system simulations, but generic components tend to simulate more slowly than their manually-written specialized counterparts. So a system modeler is normally forced to choose between building a simulation quickly or running it quickly.This paper explores the use of program specialization as a way to address this conundrum. Through hints provided by the author of a generic library and aggressive compiler optimizations, program specialization can automatically rewrite a generic component into a specialized one with performance comparable to a careful manual implementation. As a result, the user of such a specializable library can quickly assemble a simulation from generic components whose performance can equal that of a more tedious implementation.Experimental results show that program specialization provides a three- to seven-times speed-up on an important class of simulations: signal processing kernels in SystemC that manipulate fixed-precision numbers

Retrocomputing on an FPGA: Reconstructing an 80's-Era Home Computer with Programmable Logic

The author reconstructs a computer of his childhood, an Apple II+

Functioning Hardware from Functional Programs

To provide high performance at practical power levels, tomorrow’s chips will have to consist primarily of application-specific logic that is only powered on when needed. His paper discusses synthesizing such logic from the functional language Haskell. He proposed approach, which consists of rewriting steps that ultimately dismantle the source program into a simple dialect that enables a syntax-directed translation to hardware, enables aggressive parallelization and the synthesis of application-specific distributed memory systems. Transformations include scheduling arithmetic operations onto specific data paths, replacing recursion with iteration, and improving data locality by inlining recursive types. A compiler based on these principles is under development

Making cyclic circuits acyclic

Cyclic circuits that do not hold state or oscillate are often the most convenient representation for certain functions, such as arbiters, and can easily by produced inadvertently in high-level synthesis, yet are troublesome for most circuit analysis tools. This paper presents an algorithm that generates an acyclic circuit that computes the same function as a given cyclic circuit for those inputs where the cyclic circuit does not oscillate or hold state. The algorithm identifies all patterns on inputs and internal nodes that lead to acyclic evaluation orders for the cyclic circuit, which are represented as acyclic circuit fragments, and then combines these to produce an acyclic circuit that can exhibit all of these behaviors. Experiments results suggest this potentially exponential algorithm is practical for small circuits and may be improved to handle larger circuits. This algorithm should make dealing with cyclic combinational circuits nearly as easy as dealing with their acyclic counterparts