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Embedded Systems with HDLs

This document provides an introduction to embedded systems course CS60087 and hardware description languages (HDLs). It discusses the motivation for using HDLs, including specifying a design's goals, separating behavior from implementation, and synthesizing hardware from behavioral models. The advantages of HDLs are listed as supporting different abstraction levels, early functional simulation, automatic gate-level synthesis, early design space exploration, and design reuse. A brief comparison of VHDL and Verilog is given around their origins, syntax, modeling styles, and synthesizability. Finally, the document outlines the typical HDL implementation cycle from description and logic synthesis to place and route and physical design.

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210 views9 pages

Embedded Systems with HDLs

This document provides an introduction to embedded systems course CS60087 and hardware description languages (HDLs). It discusses the motivation for using HDLs, including specifying a design's goals, separating behavior from implementation, and synthesizing hardware from behavioral models. The advantages of HDLs are listed as supporting different abstraction levels, early functional simulation, automatic gate-level synthesis, early design space exploration, and design reuse. A brief comparison of VHDL and Verilog is given around their origins, syntax, modeling styles, and synthesizability. Finally, the document outlines the typical HDL implementation cycle from description and logic synthesis to place and route and physical design.

Uploaded by

penatic
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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HDL

INTRODUCTION
Course: Embedded systems (CS60087)
Prepared By: Vidya Govindan (TA)

2016 CS60087
Building Digital Systems

Problem statement

Behavioral
Description
Boolean Logic and
State
Hardware
Implementation

2016 CS60087
Building Digital Systems with HDLs

Problem statement

Behavioral
Description

HDL Description

Hardware
Implementation

2016 CS60087
Motivation for HDLs
A specification is an engineering contract that lists all the goals for a project:
Goals include area, power, throughput latency, functionality, test coverage, costs(NREs costs) etc.
Helps you figure out when youre done and how to make engineering tradeoffs. Later on goals
help remind everyone (especially management) what was agreed to at the outset!
Top down design: partition the project into modules with well defined interfaces so that each
module can be worked on by a separate team.
for eg. well defined ISA
A behavioral model serves as an executable functional specification that documents the exact behavior
of all the individual modules and their interfaces. Since one can run tests , this model can be refined
and finally verified through simulation.
We need a way to talk about what hardware should do without actually designing the hardware itself,
i.e., we need to separate behavior from implementation. We need a

Hardware Description Language


If we were then able to synthesize an implementation directly from the behavioral model, wed be in
good shape!

2016 CS60087
Advantages of using HDLs
Designs can be described at various levels of abstractions
Addresses the current digital system complexity and makes design of larger systems easier.
Describe what you need the hardware to do, tools then design the hardware for you.
Functional Simulation Early in the Design Flow
Allow modeling and simulating the functional behavior and timing of digital hardware.
Simplified & faster design process.
Automatic Conversion of HDL Code to Gates
Synthesis tools take an HDL description and generate a technology-specific netlist.
Lessen the time spent debugging the design
Design errors still possible, but in fewer places generally easier to find and fix.
Early Testing of Various Design Implementations
Due to fast synthesis, there is a scope for trying different implementations.
Design Reuse
Dont manually change all transistors for rule change.
Technology independence, standardization, portability, ease of maintenance.

2016 CS60087
A Tale of Two HDLs
VHDL Verilog
Initially created for ASIC synthesis Initially an interpreted language for gate-level
simulation.
ADA-like verbose syntax, strongly and richly C-like concise syntax, weakly and limited typed
typed language language.
Strong support for package management No special extensions for large designs.
and large designs.
Design is composed of entities each of Design is composed of modules.
which can have multiple architectures. A
configuration chooses what architecture is
used for a given instance of an entity.
Behavioral, structural, logic-level modeling Behavioral, structural, logic-level modeling
Synthesizable subsets Synthesizable subsets
Harder to learn and use, lacks language Easy to learn and use, fast simulation.
defined simulation commands.

2016 CS60087
Synthesis of HDLs
So, we have an executable functional specification that
documents exact behavior of all the modules and their interfaces
can be tested & refined until it does what we want.
An HDL description is the first step in a mostly automated process to build an
implementation directly from the behavioral model.

HDL Logic Gate Level FPGA


Description Synthesis Place & Route ASIC
Netlist

HDL-> logic create floor plan blocks


Map to target library Functional place cells in block Physical
Optimize speed, area Design route interconnect Design
(Front End) optimize (iterate!) (Back End)

2016 CS60087
HDL Implementation Cycle

2016 CS60087
References

Slide source
Comparision of HDLs

2016 CS60087

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