when you are home 时间状语从句
give a call to let me know you have arrived safely 是祈使句,作主句
找好主句的主谓宾,主语是隐含的you,谓语是give ,宾语是a call ,to let…是不定式作目的状语,前面的“当你到家的时候”是时间状语从句.