A general scheduling methodology is presented that can be integrated into specialized or general-purpose high-level synthesis systems. An initial version of the force-directed scheduling algorithm at the heart of this methodology was originally presented by the authors in 1987. The latest implementation of the logarithm introduced here reduces the number of functional units, storage units, and buses required by balancing the concurrency of operations assigned to them. The algorithm supports a comprehensive set of constraint types and scheduling modes. These include multicycle and chained operations; mutually exclusive operations; scheduling under fixed global timing constraints with minimization of functional unit costs, minimization of register costs, and minimization of global interconnect requirements; scheduling with local time constraints (on operation pairs); scheduling under fixed hardware resource constraints; functional pipelining; and structural pipeline (use of pipeline functional units). Examples from current literature, one of which was chosen as a benchmark for the 1988 High-Level Synthesis Workshop, are used to illustrate the effectiveness of the approach. >

Force-directed scheduling for the behavioral synthesis of ASICs

An integer linear programming (ILP) model for the scheduling problem in high-level synthesis is presented. In addition to time-constrained scheduling and resource-constrained scheduling, a scheduling problem called feasible scheduling, which provides a paradigm for exploring the solution space, is constructed. Extensive consideration is given to the following applications: scheduling with chaining, multicycle operations by nonpipelined function units, and multicycle operations by pipelined function units; functional pipelining; loop folding; mutually exclusive operations; scheduling under bus constraint; and minimizing lifetimes of variables. The complexity of the number of variables in the formulation is O(s*n) where s and n are the number of control steps and operations, respectively. Since the as soon as possible (ASAP), as late as possible (ALAP), and list scheduling techniques are used to reduce the solution space, the formulation becomes very efficient. A solution to a practical problem, such as the fifth-order filter, can be found optimally in a few seconds. >

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A formal approach to the scheduling problem in high level synthesis

A design methodology for automated mapping of DSP algorithms into VLSI architectures is presented. The methodology takes into account explicit algorithm requirements on throughput and latency, in addition to VLSI technology constraints on silicon area and power dissipation. Algorithm structure, design style of functional units, and parallellism of the architecture are all explored in the design space. The synthesized architecture is a multibus multifunction unit processor matched to the implemented algorithm. The architecture has a linear topology and uses a lower number of interconnects and multiplexer inputs compared to other synthesized architectures with random topology having the same performance. The synthesized processor is a self-timed element externally, while it is internally synchronous. The methodology is implemented in a design aid tool called SPAID. Results obtained using SPAID for two DSP algorithms compare favorably with other synthesis techniques. >

Architectural synthesis for DSP silicon compilers

Synthesis algorithms that offer a technique for scheduling operations and allocating registers and buses in light of both timing constraints and available hardware resources are presented. They enhance current scheduling techniques by using a global priority function that minimizes storage, interconnections, and functional unit cost. Algorithms for allocating registers and buses minimize storage and interconnection costs and take into account the interdependence of both tasks. The algorithms are also applicable to more than one method of synthesis; although first implemented in the HAL system, they have since been integrated into more specialized high-level synthesis systems. >

Algorithms for high-level synthesis

The ability to predict area-delay characteristics of designs without actually implementing them is important in producing quality designs in a reasonable time. A mathematical model for predicting the area-delay tradeoff curve for pipelined and nonpipelined data paths, given a data flow graph and a choice of module styles, is proposed. The model has been validated against designs generated by pipelined and nonpipelined data-path synthesis programs. >

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Papers

VLSI design synthesis with testability