Always-on devices typically employ a processor that is optimized for sensor processing tasks to meet the very strict power consumption requirements. In smartphones, this is a separate processor next to the main application processor, while in smaller devices, like fitness bands, it may be the only processor in the system. The tasks to be performed by the processor are a mixture of control tasks and digital signal processing (DSP) tasks.
A characteristic of always-on devices is that they operate in different modes. For example, an “always-listening” device typically deploys a detection mode in which it monitors the microphone input for someone speaking. If a voice input is detected it switches to recognition mode and applies DSP algorithms for recognizing spoken phrases. Processors in always-on systems need to support such mode switching and adjust for optimal power consumption in each mode.
For typical always-on, battery-based applications, the DesignWare® ARC® EM5D and EM7D processors include various hardware features to reduce power, or more accurately, reduce the energy needed to perform a given task.