Branch to GO_UPDATE_M1 to get out of PWM_STOP mode. Function will
stop (block) until there is new data on the control channel.
use clrbuf instead of just outputting new values in PWM_STOP mode to
avoid glitch on low-side
PWM will now restart correctly. It is necessary that the ADC is
triggered while the PWM is stopped. So at the moment this only works
when LOCK_ADC_TO_PWM is set!