For the topping, in the bowl of an electric mixer fitted with a paddle attachment, combine the flour, remaining 1/2 cup of sugar, the brown sugar, salt, and oatmeal. With the mixer running on low speed, add the butter and mix until the dry ingredients are moist and the mixture crumbles. Sprinkle topping over the fruit, covering it completely, and bake for 1 hour, until the fruit is bubbling and the top is golden brown.