birchos kriyas shema and smichas geulah l'tefilah

Rashi (Brachos 2a) writes that if ma’ariv is davened before dark one fulfills the mitzvah of kriyas shema by reciting it before going to sleep. Tosfos rejects this position, and among the objections raised is the fact that shema said before going to bed is said without the context of birchos kriyas shema and without fulfilling smichas geulah l’tefillah. Tosfos’ position underscores again the fact that the full kiyum of shema requires saying shema with its brachos (Rashi may disagree). Tosfos also assumes that smichas geulah l’tefilah is not just a din in tefilah, i.e. shmoneh esrei should be recited after the bracha of geulah of birchos shema, but it is a din in the mitzvah of kriyas shema, i.e. the mitzvah of shema is properly fulfilled only if it is followed by the bracha of geulah leading to shmoneh esrei (and again, Rashi may take the opposite position).