CPU

`init()`

Set RAM and registers to 0

`tick()`

tick_dma()
tick_clock()
tick_interrupts()
tick_instructions()

`tick_dma()`

if DMA register is set, copy RAM from source to OAM

`tick_clock()`

Update timer registers (TIMA, TAC, TMA)

`tick_interrupts()`

fire off interrupts that are queued and enabled

`tick_instructions()`

if the previous instruction was long (taking several cycles), burn off the extra cycles
look at ram[cpu.PC]
execute the instruction