说明：  该源代码主要能实现的是三种波形的输出，分别为三角波、方波、锯齿波。并且能对波形的频率进行增大或者减小。
(The source code is mainly to achieve the output waveform of the three, namely triangle wave, square wave, sawtooth wave. The frequency of the waveform and can be increased or decreased.)