@startuml
class PLLClock {
-Clock clockSource
}
class USBClock {
-Clock clockSource
}
class SYSClock {
-Clock clockSource
}
class HClock {
-Clock clockSource
}
Clock <|.. USBClock
Clock <|.. PLLClock 
Clock <|.. SYSClock 
Clock <|.. HClock 
USBClock -- "clockSource" PLLClock
HClock -- "clockSource" SYSClock 
@enduml