if you are looking to use a SAM MCU from Microchip and you want to run the CPU at 48MHz using DFLL clock source you will find an example for
SAMD21 Xplained pro.
SAML21 Xplained pro.
SAME54 Xplained pro .
SAMD11 Xplained pro.
based on ASF4 and you will find Atmel start files if you want to build your project based on it easily.for more info and full article you can visit my Website here