you don't need to double buffer to amortize the copy time. That is you don't need to do all of the copying in the vertical sync time. As long as you stay ahead

you don't need to double buffer to amortize the copy time. That is you don't need to do all of the copying in the vertical sync time. As long as you stay ahead of the raster you can spread the copy over the subsequent frame. So in my scrolling routine I start copying the top portion and work my way down the screen to stay ahead of the raster. Interrupts still fire during this time and handle some game updates / joystick reads.