Thanks for your recommend, @joan. Acctually I'm have chaotised to resolve this probem. I have used piscope to observe behavior of waveform how when I change duty cycle on set(pin, dc) function that you guided me but it seems not accurately as things I want. I can't observe when pulse start generated and to must delay it how? Can I observe all pulses generated on GPIO in realtime by piscope? acctually I'm not still understand how set(pin,dc)function operate as http://raspberrypi.stackexchange.com/questions/54859/can-any-library-generate-25-square-wave-40khz-on-gpio-pin-of-raspberry-pi-2-mode/54992?noredirect=1#comment83312_54992

Thanks for your recommend, @joan. Acctually I'm have chaotised to resolve this probem. I have used piscope to observe behavior of waveform how when I change duty cycle on set(pin, dc) function that you guided me but it seems not accurately as things I want. I can't observe when pulse start generated and to must delay it how? Can I observe all pulses generated on GPIO in realtime by piscope? acctually I'm not still understand how set(pin,dc)function operate as https://raspberrypi.stackexchange.com/questions/54859/can-any-library-generate-25-square-wave-40khz-on-gpio-pin-of-raspberry-pi-2-mode/54992?noredirect=1#comment83312_54992