What is the standard of procedure on appeal?

Counsel was appointed to represent defendant on appeal. Counsel filed an opening brief setting forth the facts of the case and requesting this court to review the record and determine whether there were any arguable issues on appeal. (People v. Wende (1979) 25 Cal.3d 436 (Wende).) Counsel advised defendant of his right to file a supplemental briefing within 30 days of the date of filing of the opening brief. More than 30 days elapsed, and we received no communication from defendant.