Real-time clock generation device and real-time clock generation method

A real-time clock generation device comprising:

• a first ring oscillator that outputs a reference clock signal;
• a table acquirer that acquires a control-value table representing a correspondence between time zones in which the first ring oscillator operates and division ratios of the reference clock signal;
• a divider that, in accordance with the control-value table, generates a real-time clock signal by changing the division ratio of the reference clock signal for each time zone in which the first ring oscillator operates;
• a second ring oscillator that, during execution of calibration of the control-value table, outputs a measurement clock signal that oscillates more accurately than the reference clock signal;
• a frequency measurer that measures a frequency of the real-time clock signal based on the measurement clock signal;
• and
• an update determiner that determines whether a frequency of the real-time clock signal measured by the frequency measurer is equal to or smaller than a predetermined allowable error, updates at least part of the division ratios in the control-value table in a case in which the frequency of the real-time clock signal exceeds the allowable error, and ends the calibration in a case in which the frequency of the real-time clock signal is equal to or smaller than the allowable error.