Ruling at the End

i didnt see a thread about it, was wondering if some with knowledge about rules could help.evans gets tackled with 15 seconds left.  the clock runs till 8 seconds.  then the game is called for injury timeout when the trainers come out onto the field.is the 7 seconds running off the clock normal?  i assume the clock stops until the ball is placed or does the clock run nonstop?  was the clock actually stopped at 8 because of the trainers running onto the field or to set the ball and first down markers?just trying to get a feel if it was all legit.  doesnt matter, but still curious.