In order to play the tone, every sample needs to be sent to the DAC at a specific rate that depends on the frequency of the tone, the number of samples in the sine wave table and the frequency of the TIMER peripheral that is responsible for sending the samples to the DAC tone, 45 samples, 25MHz timer: In one second (25 million cycles), 440 full periods (i.e. 45 samples) need to be sent to the DAC. Hence, Dac_SamplesTimer needs to be set to 25MHz (duration of a second) / (440 * 45) = 1250Hz