Motion in arrest of judgment

(a) POWER OF THE COURT. The court, on written motion of the defendant or on its own motion, shall arrest judgment if the charging instrument does not charge an offense, or if the court was without jurisdiction of the offense charged. (b) TIMELINESS. A motion in arrest of judgment shall be filed within thirty (30) days after sentence is pronounced. The court may act on its own motion in arresting judgment only during the period in which a motion in arrest of judgment would be timely.