Space Invaders on an ARM Cortex M

This is a TI TM4C123G Launchpad and Nokia 5110 display, with an R2R Ladder circuit DAC for 4 bit sound output.  I created the game using the Keil free version compiler just bumping up to the edge of the 32K limit.  This was for an online class I was taking from EDX: Embedded Systems Shaping the World.