Common Design Patterns for Symbian OS: The Foundations of Smartphone Software

Chapter 4. Event-Driven Programming

Power conservation is important in mobile devices since battery life is usually one of the top three reasons a consumer will choose a particular device. Mobile software must be designed to be frugal in its use of hardware components that consume power, such as the CPU, display and radio units. These power-sink hardware components usually have various modes of operation including low-power modes which can be used to minimize power drain whenever the hardware components, or software services related to them, are not in use. An example of a power-sink component and a related service might be a Bluetooth radio unit and a Bluetooth device discovery service. Such hardware components are often encapsulated as shared resources in Symbian OS and are managed on behalf of the programs that use them (often using a reference counting mechanism).

One power-sink hardware component that all programs utilize is the CPU. The software running on a mobile device has a direct influence upon the power consumed by the CPU. This is because the CPU uses power for each CPU cycle executed. The fewer CPU cycles needed to execute a piece of functionality, the less power the device uses. This applies to all types of software, from device drivers for hardware resources to user-level applications. All Symbian developers should understand and apply these patterns throughout their software design and development.

Consider an indicator on a mobile phone that shows whether a Bluetooth ...