Introduction
- Prerequisites
- Textbook
- Course accounts and ERC 208
- Laboratory assignments and use of Mentor Graphics Tools
Introduction
- 1960's - 1980's
- AHPL, CDL, DDL in classroom. Number of languages mushrooms to over 200 languages, all of them either proprietary or academic
- 1983 VHSIC Program initiates definition of VHDL
- 1987 VHDL Standard (IEEE 1076) approved
- 1990 Verilog dominates the marketplace.
- VHDL gaining acceptance as the
second language due to standards effort and DoD mandated use.
- 1992 IEEE 1164 (3, 4, 9-valued logic standard adopted)
- 1993 VHDL re-balloted
- minor changes make it more user-friendly.
- 1994 Widespread acceptance of VHDL.
- CAE tools operate at speeds comparable to Verilog. Mentor, Cadence, Viewlogic, Synopsys all provide full VHDL compilation / simulation and synthesize with subsets of VHDL.
It is important to understand that hardware description languages (HDLs) exist to satisfy a variety of purposes and are used in a number of different ways. Therefore, there are features of VHDL (and any other design language) that will be useless in some applications, and confusing in other applications. Some descriptive features of VHDL may even lead to bad synthesis. A major aspect of this course will be understanding how VHDL should be used to permit synthesis tools to produce good implementations of designs.
To understand why VHDL looks the way it does, it will help to examine the variety of purposes it serves.
- Definition of functional interfaces
- concurrent ==> structure (space)
- sequential ==> behavior (time)
- Definition of functions of the design (behavior)
- by control flow (procedural)
- by data flow (concurrent)
- Project partitioning
- in space (structural)
- in time (behavioral)
- Language standardization
- to improve quality and efficiency of
communication, broaden audience
- Interface description for users
- often as components of next level
higher system: physical, structural, and "pin"
functions
- Express usage constraints
- e.g. disallowed input timings, combinations,
output loads
- Express functional behavior of the design:
- internal states,
data structures (e.g. format used in a floating point unit) algorithms
implemented
- Show communication protocols between design entities
- SIMULATION -- The Usual Method
- highly developed tools
- inherently behavioral (structural simulators consist of ordered
calls to primitive procedures to model corresponding primitive structures)
- limited by the effectiveness of the design test program developed
- Formal verification methods require
- common language for: specification of design goals and
description of implementation to meet those goals
- formal (mathematically rigorous) language definition to permit
logical transformation of descriptions to prove equivalence.
Such mathematical languages inherently are declarative
- language that can describe both time and structure
- Correctness by construction (silicon compilation) is more nearly realized
than automatic verification systems
This is Dr. Huey's primary area of research, and a major topic of CSE 516.
- stepwise refinement of design by architectural decomposition (either
structural or behavioral)
- transformations from behavioral models to corresponding structural
and physical models
e.g. PLA generators, standard cells for shift registers, adders, etc.
- relating scaling parameters with expressions
- enforcement of design constraints
- register transfer level allocation, dataflow optimizations<
- expression transformations for optimization
- Standardization of Documentation
- improved communication of requirements between military, contractors,
and subcontractors
- System Design Time and Cost
- reduced ambiguity in specification of design interfaces and design
functions
- reusability of existing designs
- Open-system CAE Tools
- can change CAE system without losing use of existing designs
elimination of language translators
- Improved Integration of Multi-vendor Designs
- shared design databases become possible -- standard cells, behavioral models
- Improved Understanding of Design Science
- top-down, middle-out, bottom-up
Copyright 1995, Ben M. Huey
Copying this document without the permission of the author is prohibited
and a violation of international copyright laws.
Rev. 8/31/95 B. Huey