Book excerpt: High-level synthesis blue book - part4

9/25/2012 10:53 AM EDT

High-level synthesis blue book - Michael Fingeroff - Calypto

The promise of high-level synthesis (HLS) is a powerful one: the ability to generate production-quality register transfer level (RTL) implementations from high-level specification. In other words, HLS automates an otherwise manual process, eliminating the source of many design errors and accelerating a very long and iterative part of the development cycle.

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Chapter listing

Similar to loop pipelining and loop unrolling, the way in which IO and memory accesses are coded in a design can have a significant impact on both area and performance. IO and memory accesses tend to be the bottleneck in a system and they can potentially limit the ability to pipeline a design, or negate the benefits gained from loop unrolling. In the worst case using bad style when coding IO or memories prevents scheduling a design.

There are two primary ways for passing IO into and out of a design, pass by value and pass by pointer or reference, which includes arrays. Using one over the other can lead to very different behavior.

Chapter contents (highlighted subject will be provided)

Unconditional IO

Conditional IO - new this week

Memories

Introduction

The previous chapters provided a good introduction to the principles behind high-level synthesis and the use of bit-accurate data types. The basics of scheduling and loop optimizations were illustrated using concepts familiar to RTL designers, such as hardware diagrams, state machines, and timing diagrams. The next logical step is to take this foundation and apply it to some real world hardware examples. In a similar fashion to most RTL design guides, this chapter presents many of the basic hardware structures that RTL designers are familiar with, and shows how to code them using synthesizable C++. Unlike the examples of previous chapters, which focused primarily on a C-like coding style, class-based/object oriented C++ is introduced, including templates and recursion. As this chapter progresses the reader can begin to see the true power of hardware design using C++. The hardware examples presented in this chapter are all depicted as sequential circuits. This is because it is assumed that each example is synthesized as the top-level design. When used in the context of a larger design these circuits may be sequential or combinational based on the clock frequency and how the design is scheduled. True combinational components can also be synthesized by using explicit directives in the C++ synthesis tool.

Chapter contents (highlighted subjects will be provided in excerpts)

Shift Registers 

Helper Classes for Design Reuse

Multiplexors

Priority Search Hardware

Shifters

Adder Trees

Lookup Tables (LUT)

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