Spiral model of embedded software life cycle

The spiral model develops embedded software through repeated cycles (spirals), each passing through the same four phases. Each cycle produces a more complete prototype, and risk analysis is done before the next cycle. It suits large, complex embedded products with uncertain requirements.

 Planning ----------> Risk analysis
    ^                      |
    |                      v
 Evaluation <------- Engineering
 (each loop = one prototype; loops spiral outward)

Phases of each spiral

1. Planning / objectives: determine the objectives, requirements, constraints (cost, memory, timing) and alternatives for this cycle.
2. Risk analysis: identify and evaluate technical risks (e.g. missed deadlines, hardware issues) and reduce them using prototypes, simulation or analysis.
3. Engineering (development and testing): design, code, integrate and test this cycle's version (first a prototype, then more complete versions).
4. Customer evaluation: the customer reviews the result, and the feedback is used to plan the next spiral.

Features

• Combines the waterfall model with prototyping and adds risk analysis.
• The radius of the spiral represents cost; the angle shows progress.
• Early cycles produce a concept and prototype; later cycles produce the final product.

Advantages: risks are found early; changes in requirements are easy to handle; good for hardware-software co-design. Disadvantages: needs risk-analysis expertise; can be costly and long; not suited to small projects.