Patent ID: 8907688

Claim:
A clock supplying device for supplying a clock signal for use in an operation of a communication apparatus, comprising: a first oscillator configured to generate a first clock signal; a second oscillator configured to generate a second clock signal; first measurement circuitry configured to acquire a reference clock signal extracted from a transmission line coupled to the communication apparatus, and to measure a first frequency difference between the first clock signal and the reference clock signal; second measurement circuitry configured to acquire the reference clock signal, and to measure a second frequency difference between the second clock signal and the reference clock signal; and a first determiner configured to determine whether warm-up operations of the first oscillator and the second oscillator have been completed or not, in accordance with measurement results of the first and second frequency differences, and to control which of the clock signals of the oscillators set as usable in accordance with the determination, wherein the first determiner comprises a state manager configured to manage a state of units comprising the first and second oscillators, and wherein the state manager comprises: a generator configured to generate a warm-up notification relating a warm up state of the first and second oscillators, a power monitor configured to provide a start of power notification upon a start of power supply to the first and second oscillators, and a second determiner configured to receive the measurement results of the first and second frequency differences and the start of power notification and to notify t generator of the warm up state in the first and second oscillators in accordance with the measurement results of the first and second frequency differences and a time elapsed after the start of power supply.