I have 2 clocks in my design. One slow External clock and one high frequency ring oscillator clock. For external clock I am using the create_clock command to specify timing. The ring oscillator block is instantiated inside my design. Now how do I specify the constraint for the ring oscillator pin? My understanding is that create_generated_clock isn't relevant in this case since ring oscillator clock is not generated from any other clock and is asynchronous to other clock.