Tex. Fin. Code § 306.102

An amount that is paid, passed through, or obligated to be paid or to be passed through in connection with asset-backed securities or that is not paid as a result of a discounted sale price to the holders of asset-backed securities by a pass-through entity is not interest. This section does not affect interest that is agreed on and fixed by the parties to a written contract and paid, charged, or received on the ultimate underlying assets pledged to or held for the benefit of holders of asset-backed securities.