In recent years, a serial interface which connects devices to each other has been widely used. The serial interface can perform high-speed data transfer between the devices. Many devices that require high-speed data transfer support the serial interface. Examples of the devices include various electronic devices. Each of the devices can communicate with a host via the serial interface between the device and the host.
In addition, each of the devices may transition from a normal operation state to a low-power state by negotiation with the host. For example, according to active state power management (ASPM) which is a protocol defined in the PCI Express specification, only when a function of the ASPM is enabled by the host, the device can start the transition from the normal operation state to the low-power state.
Therefore, even in a case where no data are transferred via a link, if the function of ASPM is not enabled by the host, the device cannot enter the low-power state. This causes an increase in power consumption of the device.