I'm using an external 32.768kHz crystal that I will use for RTC too (so it should have a high accuracy). I'm trying to use it as the reference for DFLL48 in closed-loop mode. As I described in another post, unfortunately the initialization sometimes hangs forever because the DFLL fine lock isn't never reached.
So I'm asking what are the real differences between open and closed loop. In open loop I shouldn't need to wait for fine lock, so it should be a safer choice. What are the problems with the open loop mode?
I don't think I need high accuracy for the clock. I only use SERCOM in UART mode with 115200bps baudrate.