Thank you. I am grateful for your reply. I started to use the pin's capability of callback. It is unfortunate the pwm call is not supported yet in the documentation. What is the best way to report bugs? If this is true, it is confusing to users of Pycom.

@VST-Admin The actual example in the in the examples section documentation mentions alarm.callback(None). The recent firmware supports the cancel method. So I recommend updating the firmware.