Electronic devices such as electronic book readers (“e-book readers”), cellular telephones, portable media players, desktop computers, laptops, tablet computers, netbooks, personal digital assistants, and the like, rely on electrical power to function.
Within these electronic devices, several components utilize significant amounts of power during operation, including the processor(s) and peripheral devices. These peripheral devices include external memory interfaces (EMIs), Universal Serial Bus (USB) controllers, image processing units (IPUs), and so forth. These peripheral devices may reside on the same “chip” or die as the processor, be on another die, or a combination.
A processor not actively in use, but idling, continues to consume significant quantities of power. This idling wastes energy as well as increasing the amount of heat dissipated by the electronic device. Reducing power consumption increases the usable time for a portable device operating from a battery. Reducing power consumption also reduces the heat dissipated by the electronic device, allowing it to operate at a cooler temperature and thus increasing the life of the equipment and simplifying design for cooling.
Various schemes have been put forth to reduce power consumption in portable consumer devices by placing the processor of the device and the peripherals into a “doze” mode. Typically, entering the doze mode involves turning off unused portions of the circuit and/or reducing clock speed of the microprocessor.
However, the techniques used to enter the doze mode introduce unacceptable latencies to execution of commands upon resumption of normal activity. Additionally, recurrent timer interrupts often prevent a device from entering doze mode, or from remaining in doze mode long enough to realize a meaningful reduction in power consumption.