Tennessee Code Title 40. Criminal Procedure § 40-17-110

(a) Witnesses subpoenaed are bound to attend from term to term until the case is disposed of; but if a judgment is rendered in the case, which is reversed by the supreme court, or in the case of a mistrial, new subpoenas must be issued for the state witnesses, and also for the defendant's witnesses on the defendant's application.

(b) Witnesses shall so attend until discharged by law, by the court, or by the party by whom they are summoned.