Hi there,
LOL, man I vaguely remember some Fortran77 back in the 80"s ? Punch cards too. WOW
The Nrf52840 has Several timers and the PWM’s You can use either.
to achieve the outcome, Check out how Arduino generates Pulses link
Basically set the pulse length, attach an Interrupt, In the ISR reset the timer value start the duty cycle timer with interrupt and rinse and repeat.
like this one, it’s also applicable to Xiao.
HTH
GL 
PJ
I’ll look at the blink_print time permitting 
and make some comments. 