Turbo Redemption Debt Modeling

Hoping someone could help with modeling a Term Loan with a Turbo Provision?

Specifically the Term Loan should be structured as following;

• Fully Amortizing Debt Service
• If there is excess revenue in year X then par in the longest dated amortizing period should be paid off, hence a “Turbo” Redemption

I feel like I’m over thinking this.

In theory this is pretty simple, but how do I calculate this without circularity? Or if I do need circularity, can someone point me in the direction of how to create a circularity breaker?

Thanks for all the help!