Interlaced frames to improve performance

[MooseTheGoose]

The Nordic nRF52840 has 32 MHz SPIM interfaces to communicate with the ILI9341 display, which requires us to send 16 (bits per pixel) * 320 (pixels per row) * 240 (rows per screen) bits. This means that, at minimum, updating the entire display takes

((16 * 320 * 240 bits) / (33554432 bps)) = 0.03662 seconds = 36.62 ms.

However, there is a trick called Interlacing that requires us to only update half the screen. There's precedence for it being used in video game consoles as well.

If you look at the links above, you'll see interlacing does not come without its problems, but the performance gains may be worth it, especially because we output video in realtime rather than still images. It would cut down frame update times from 36.62 to 18.31 ms.