A method and circuitry for generating a trigger signal based on an oscillation signal and associated non-transitory computer program product are provided. The method includes following steps. Firstly, a calibration value is obtained according to a reference frequency and a frequency of the oscillation signal, and a counting value is gradually altered from a first initial value to a breakpoint value. Secondly, the counting value is updated to a second initial value when the counting value is equal to the breakpoint value. Then, the counting value is gradually altered from the second initial value to a final value, and the trigger signal is generated when the counting value is equal to the final value.