Thursday, October 21, 2010

Embedded Software Risk Areas -- Design

Series Intro: this is one of a series of posts summarizing the different red flag areas I've encountered in more than a decade of doing design reviews of industry embedded system software projects. You can read more about the study here. If one of these bullets applies to your project, you should consider whether that presents undue risk to project success (whether it does or not depends upon your specific project and goals). The results of this study inspired the chapters in my book.

Here are the Design red flags:
  • Design is skipped or is created after code is written
Developers create the design (usually in their heads) as they are writing the code instead of designing each module before that module is implemented. The design might be written down after code is written, but usually there is no written design. As a result, the structure of the implementation is messier than it ought to be.
  • Flowcharts are used when statecharts would be more appropriate
Flowcharts are used to represent designs for functions that are inherently state-based or modal and would be better represented using a state machine design abstraction. Associated code usually has deeply nested, repetitive “if” condition clauses to determine what state the system is in, rather than having an explicit state variable used to control a case statement structure in the implementation. The result is code that is significantly more bug prone code and difficult to understand than code based on a state-machine based design.
  • No real time schedule analysis
There is no methodical approach to real time scheduling. Typically an ad hoc approach to real time scheduling is used, frequently featuring conditional execution of some tasks depending upon system load. Testing rather than an analytic approach is used to ensure real time deadlines will be met. Often there is no sure way to know if worst case timing has been experienced during such testing, and there is risk that deadlines will be missed during system operation.
  • No methodical approach to user interface design
The user interface does not follow established principles (e.g., [5]), making use of the product difficult or error-prone. The interface might not take into account the needs of users in different demographic groups (e.g., users who are colorblind, hearing impaired, or who have trouble with fine motor control).

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