* Chip8 Emulator

** The memory Layout

The Chip8 has 4095 bytes of memory:

#+begin_src artist
  +-----------------------+
  |                       | 0xFFF - End of Memory
  +-----------------------+
  |                       |
  |                       |
  |                       |
  |     0x200/0xFFF       |
  |     ProgramData       |
  |                       |
  |                       |
  +-----------------------+ 0x200 - Start of Chip8 programs
  |                       |
  |      0x00/0x1FF       |
  |   Reserved for Chip8  |
  |                       |
  +-----------------------+ 0x00 - Start of Chip8 RAM
#+end_src

Chip-8 has a stack that is an array of 16 16-bit values, used to store the
addresses that the Chip8 should return to when returning from a subroutine,
meaning there can be 16 levels of nested subroutines.

** Registers

Chip8 has 16 8-bit data registers, each can hold 1 byte of information.

| Data Registers |
|----------------|
| V0             |
| V1             |
| V2             |
| V3             |
| V4             |
| V5             |
| V6             |
| V7             |
| V8             |
| V9             |
| VA             |
| VB             |
| VC             |
| VD             |
| VE             |
| VF             |

That means that the registers should be implemented as an array with a size of
16:

| V0 | V1 | V2 | V3 | V4 | V5 | V6 | V7 | V8 | ... |

The Chip 8 also has some extra registers:
- *I* - used to store memory addresses.
- *PC* - points to the address oft he current instruction being executed. All the
  instructions are 2 bytes in size, so this should be incremented by 2 per
  instruction executed.
- *SP* - 8-bit stack pointer, points to a location in the stack.
- *Sound Timer*:
  - Chip8 plays a beep when the sound timer is not zero
  - Decrements at a rate of 70hz
  - When zero no sound is played
- *Delay Timer*:
  - Chip8 stops executing instructions when the delay timer is greater than
    zero.
  - This is also decremented at a rate of 60hz.
  - When the delay timer is zero, the program execution resumes.

** The Display

The size of the display is 64x32 pixels, and it's monocrome. Drawing to the
display is done with sprites, not pixels. If a sprite overflows the screen, it
wraps it back to the other side. The sprites can be a maximum of 8 bits of
width, and up to 15 bytes in length.

** The Keyboard

The Chip-8 keyboard has 16 keys: from 0 to F.

This is how the keyboard looks:

| 1 | 2 | 3 | C |
| 4 | 5 | 6 | D |
| 7 | 8 | 9 | E |
| A | 0 | B | F |

** Instruction Set

The Chip-8 instruction set has 36 different insturctions. These instructions can
be for mathematical operations, drawing and more.