Application Defined Processors

By rebuilding a system's logic on the fly, this project can make one FPGA do the work of tens or hundreds of ordinary processors.
Programming Model for Reconfigurable Computing

Traditionally, the programming model for RC has been one of hardware design. Given that the tools required for the underlying FPGA technology of RC are all logic design tools from the Electronic Design Automation industry, there really has not been a programming environment recognizable to a software developer. The tools have supported Hardware Definition Languages (HDLs) such as Verilog, VHDL and Schematic Capture.

With the introduction of system-on-a-chip (SOC) technology and the complexity associated with hardware definition of such complexity, high-level languages have begun to be available. Java and C-like languages are becoming more common for use in programming RC chips. This is a significant step forward but continues to require quite a leap by application programmers.

The SRC programming model is the traditional software development model where C and Fortran are used to program the MAP processor, and any language capable of linking with the runtime libraries (written in C) can be compiled and run on the microprocessor portion of the system.

The SRC Carte programming environment was created with the design assumption that application programmers would be writing and porting applications to the RC platform. Therefore, the standard development strategies of design, code in high-level languages (HLLs), compile, debug via standard debugger, edit code, recompile and so on, until correct, are used to develop for the SRC-6 system. Only when the application runs correctly in a microprocessor environment is the application recompiled and targeted for the DEL processor, MAP.

Compiling to hardware in an RC system requires two compilation steps that are quite foreign to programming for an instruction processor. The output of the HLL compiler must be a hardware definition language. In Carte, the output either is Verilog or Electronic Design Interchange Format (EDIF). EDIF files are the hardware definition object files that define the circuits that will be implemented in the RC chips. If Verilog is generated, then that HDL must be synthesized to EDIF using a Verilog compiler such as Synplify from Synplicity.

A final step, place and route, takes the collection of EDIF files and creates the physical layout of the circuits on the RC chip. The output files for this process are a configuration bitstream, which can be loaded into an FPGA to create the hardware representation of the algorithm being programming into the RC processor.

The Carte programming environment performs the compilation from C or Fortran to bitstream for the FPGA without programmer involvement. It further compiles the codes targeted to microprocessors into objects modules. The final step for Carte is the creation of a unified executable that incorporates the microprocessor object modules, the MAP bitstreams, and all of the required runtime libraries into a single Linux executable file. Figures 6 and 7 present the Carte compilation process.

Figure 6. Carte Programming Environment

Figure 7. Carte Compilation

Open-Source Hardware Opportunity

Linux has led the way and benefited greatly from the Open Source movement where a large and dedicated group of software developers has created, modified and improved the Linux kernel and OS at a rate, quality and level of innovation that could not be matched by the work of a single commercial organization. Reconfigurable computing has the potential of enabling such innovation and technical advances in hardware design. Much of this article is spent explaining the concept of application programmers writing code and using standard programming methods to create application-specific hardware without requiring knowledge of hardware design. However, in RC the building blocks of the generated hardware created by application programmers is the functional unit. Functional units are basic computational units such as adders, floating-point multipliers or trigonometric functions. Functional units also can be specialty high-performance units, like triple DES functions, or nonstandard precision arithmetic units, such as 24-bit IEEE floating-point operators.

Functional units are created by logic designers. RC compilers, such as SRC's Carte MAP compiler, are capable of allowing customer-supplied functional units to be added to the standard set of operations supported by the compiler. When new and novel functional units are made available to application programmers, an even higher level of performance can be achieved.

It is in the creation and sharing of innovative hardware designs for functional units where an Open Hardware movement could bring substantial advances to computational science. The innovation and productivity seen in the open-source arena could be replicated as Open Hardware.

RC provides a vehicle for many more creative designers to create new and novel hardware that can be used by application developers. Through groups like Opencores.org, functional unit design can be shared and improved upon. The significant advances seen in the computational sciences, due to open-source software, easily could be seen through a movement focused on open hardware as well.

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