Energy saving in a network processor

A network processor includes a transceiver circuit 311, a network data processing unit, and a clock signal control unit 34. The transceiver circuit transmits and receives a network signal, compares a voltage level of the network signal with a threshold value, outputs a comparison result, and operates under a first clock signal. The network data processing unit is coupled to the transceiver circuit to process the network signal, and operates under a second clock signal different from the first clock signal. The clock signal control unit disables supply of the second clock signal to the network data processing unit when the voltage level is smaller than the threshold value, and enables supply of the second clock signal to the network data processing unit when the voltage level is not smaller than the threshold value. The network processor may be adapted for connection to a computer system that includes a basic input/output system (BIOS) 36 and may send commands to the BIOS via a general purpose input/output (GPIO) causing it to output control signals to the clock signal control unit.