I know you can't talk during פסוקי דזמרה, and certainly not during ברכות קריאת שמע. What about between them? And if not talking, what about דברי תורה?
Mishna Berura 54:3:6 says that one may do any Dvar Mitzva between Yishtabach and Yotzer, however no talking is allowed. Thus one may look into a Sefer during that time, however one can not give a Shiur then.