when checking the manual of ATSAMD51G, there is following statement:
7.3.2 Starting of Clocks
Once the power has stabilized and the internal Reset is released, the device will use a 48MHz clock by default. The clock source for this clock signal is DFLL48M, which is enabled after a reset by default.
When I understand this correct, after start-up DFLL48M is running as clock source at 48 MHz. But when I have a look into Atmel START, there is no possibility to let this clock run for its own - to let it produce an 48 MHz output, an other clock source is needed.
So: how can one set up DFLL48M to be used as base clock which itself does not needs any clock source? The only thing I got working was
OSCLULP32K (32 kHz) -> GCG3 (32 kHz) -> DFLL48M (48 MHz)
which is really weird and complicated.