Where a defendant in a case of felony persists in pleading guilty or in entering a plea of nolo contendere, if the punishment is not absolutely fixed by law, a jury shall be impaneled to assess the punishment and evidence may be heard to enable them to decide thereupon, unless the defendant in accordance with Articles 1.13 or 37.07 shall have waived his right to trial by jury.
Tex. Code Crim. Proc. § 26.14