I want to do a fade in and out of an LED while the board is in sleep mode. I can easily do this in arduino, but would rather have the rockpro64 do it. Is there anything the rockpro64 can do while asleep aside from wait for a signal to wake it up?
There is a 4 Pin JST Connector just behind the Power DC Jack .... its directly connected to the power rail ... you could rig a simple circuit up completely independent of the GPIO using a 555 Timer some resistors, a tranny and and capacitors etc even safer install your own buck converted to drop the voltage down to be even saver. But I take it you wanted GPIO / PWM to avoid the complicated electronics !
I want to leave that connector alone as it's meant to share power with the 2 hard drives I have connected to it. I'd like not to mess with that.