Cook piecrust as directed on package. Meanwhile cook your blackberries in a pot on the stove. To do so, add blackberries, water, sugar and cinnamon to pot and bring to a boil. Slowly, add cornstarch mixture until the right consistency. Let cool. In a large bowl, mix Philly Cream Cheese and Cool Whip together until mixed well. Once pie crust is cool, add cream cheese mixture to crust. Top the pie with the blackberry mixture and let sit in the refrigerator 2 to 3 hours.