To make the topping, combine the flour, granulated sugar, brown sugar, salt, oatmeal, and the cold, diced butter in the bowl of an electric mixer fitted with a paddle attachment. Mix on low speed until the butter is pea-sized and the mixture is crumbly. Sprinkle evenly on top of the peaches and raspberries. Bake for 1 hour, until the top is browned and crisp and the juices are bubbly. Serve immediately, or store in the refrigerator and reheat in a preheated 350 degree F oven for 20 to 30 minutes, until warm.