How to Write an ASIC specification

Tell Me What You Want, What You Really Really Want.


Explosion of first Ariane 5 flight, June 4, 1996

Development costs for many products are measured in millions of dollars. The consequences of being late to market can be devastating to a company.  No-one expected the 1990’s band the Spice Girls to identify that one of the key issues in complex product development is the clear and unambiguous definition of the core functionality of the product, known as “Tell me what you want, what you really really want”*.

The specification is central to the on-time and on-budget development of an “application specific” integrated circuit, often described as an ASIC.  What can be done? Can a document really help? Weak definition of a product leads to costly redesign work and could result in a competitor launching their product first and taking the market. Specification of software used on the Ariane 5 rocket suffered from poor definition of detailed requirements and functionality, which ultimately led to software performing 64-bit operations with 16-bit precision but failing to correctly detect overflow conditions.  The maiden flight of Ariane 5 lasted one minute before the rocket along with the $500M payload were destroyed. This article describes the content of a typical product specification, how the specification is created and how the document is used with particular emphasis on the customer contributions.

Table of Contents

  • The 7 Pitfalls of Bad Specifications
  • Specification Audience
  • Purpose of The Specification
  • How Is the Specification Used?
  • What Are the Requirements?
  • What Make A Good Requirement?
  • Terminology
  • Specification Compliance

  • Functionality Vs Implementation
  • Production Related Functionality
  • Document Revisions
  • Document Review and Approval
  • Change Requests
  • ASIC Specification Content
  • Approvals


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