Synchronous control apparatus and method

摘要

A digital variable-frequency oscillator has an output frequency thereof variable in dependence upon a frequency control variable. Externally input data are stored in a data storage device, from which the data are generated in accordance with the output of the digital variable-frequency oscillator. A remaining data amount of the data storage device is detected in response to an externally input timing signal that is received in synchronism with the data received by the data storage device such that synchronization is performed based on the timing signal. A filtering operation is performed on values of the frequency control variable so as to calculate an average value of the frequency control variable. A new value of the frequency control variable is calculated based on the calculated average value and the difference between the detected remaining data amount of the data storage device and a target data amount thereof. The output frequency of the digital variable-frequency oscillator is controlled based on the calculated new value of the frequency control variable so as to reduce the difference between the remaining data amount of the data storage device and the target data amount thereof.