Page 41 - Embedded Microprocessor Systems Real World Design

Software specifications describe:
The requirements
Interfaces to other software
How the software implements the requirements

A Requirements Document Outline

The following is an outline for a requirements document that will fit most
products. This document describes the product as a “black box”-that is, what the
product does, not how it is done.
Overview. A brief description of the document, such as “This document
describes the requirements for the ABC corporation swimming pool timer.”
Related/reference documents. Related internal documents, such as product
specifications, environmental specifications, and the like. Related industry
specifications such as ANSI or IEEE specifications.
Specifications. These could include the following:
Agenq approvals. List agency approvals that the product must meet, such as
FDA requirements, IEC 950, UL 1950, shock/vibration specifications, and
so forth.
Requiremerzts. List system requirements. The following items are typical of the
sort of thing that might be listed, and obviously all of these items will not
apply to all products. This section is the core of the document and may
run to dozens of pages.
MTBF (mean time between failure)
MTTR (mean time to repair, usually applies to products that are serviced
by a field service organization)
Speed (How many things per minute/hour/day must be done?)
Operator interface (LCD? touch panel? barcode readers? mouse/
keypad?)
External interfaces (interfaces to other systems, to a controlling host
system, or to a slave subsystem? Ethernet? RS232? Proprietary?)
Available options (may be lengthy if several need to be described)
Input power (list input voltages, frequencies, and current; include
international requirements)
Export restrictions and requirements (applies if using controlled
technology; also, requirements for the product to be marketed in
certain countries may limit technology that can be used)

26 Embedded Microprocessor Systems