Chip-8 Emulator

Diving into emulation development at the same time as continuing to learn Rust. In doing some research, building a Chip-8 emulator is the has become the "Hello World" for emulation development.

Chip-8 is an interpreted programming lanuage developed by Joseph Weibecker for an 1802 Microprocessor. Chip-8 programs are run on a Chip-8 virtual machine, which is what I will be building an emulator for in this project. I frequently referenced and followed this guide as I worked through this project.

Chip-8 Virtual Machine Tech Specs

• 64x32 monochrome display.
  • Graphics are drawn to screen by drawing sprites which 8 pixels wide and can be 1 to 15 pixels in height.
  • Sprite pixels are XOR'd with their corresponding screen pixels.
  • Sprite pixels that are set flip the color of the corresponding screen pixel, while unset sprite pixels do nothing.
  • The carry flag (VF) is set to 1 if any screen pixels are flipped from set to unset when a sprite is drawn and set to 0 otherwise, this feature is used for collision detection.
• Sixteen 8-bit general purpose registers.
  • The register names go from V0 to VF (although the VF register doubles as a flag and should be avoided).
• 16-bit index register (I).
  • Although 16-bits, only the lower 12 bits are used for addressing purposes due to the 4KB memory size (12 bits is sufficient to address any location within this memory range).
• 16-bit program counter (PC).
• 4KB (or 4096 bytes) of memory.
• 16-bit stack for calling and returning from subroutines.
• 16-key hex keyboard input.
  • The 16 keys are labelled with hexadecimal values (0-F).
• Two special registers which decrement at 60 hertz and trigger upon reaching zero.
  • 8-bit delay timer: Used for time-based game events.
  • 8-bit sound timer: Used to trigger the audio beep.

Crates

• chip-core: Defines the backend emulator implementation.

Opcode Table

Chip-8 has 35 opcodes, which are all two bytes long and stored big-endian (meaning the most significant byte of a word is stored at the smallest memory address and the least significant byte at the largest).

Idx	Opcode	Shorthand	Description
1	0000	NOP	Do nothing. Useful for syncing timing and alignment.
2	00E0	CLS	Clear screen, reset the screen buffer.
3	00EE	RET	Return from subroutine by setting the program counter to the memory address to return the return address.
4	1NNN	JUMP	Jump to memory location NNN by setting the program counter to that memory location.
5	2NNN	CALL	Call subroutine at the memory location NNN. Push current program counter to the stack to use later when returning from the subroutine.
6	3XNN	SKIP_EQ	Skip the next instruction if value retrieved from V register X is equal to NN (VX == NN).
7	4XNN	SKIP_NEQ	Skip the next instruction if value retrieved from V register X is not equal to NN (VX != NN).
8	5XY0	SKIP_V	Skip the next instruction if value retrieved from V registers X and Y are equal (VX != VY).
9	6XNN	SET	Set the value of V register X to NN.
10	7XNN	ADD	Adds the value NN to the value in V register X (wraps on u8 overflow).
11	8XY0	SET_V	Set the value of V register X to the value stored in V register Y.
12	8XY1	OR	Set the value of V register X to the bitwise OR with the value in V register Y.
13	8XY2	AND	Set the value of V register X to the bitwise AND with the value in V register Y.
14	8XY3	XOR	Set the value of V register X to the bitwise XOR with the value in V register Y.
15	8XY4	ADD_V	Adds the value in register X to the value in register Y. Store the value in register X and set the carry flag in register F based on if the operation underflowed or overflowed.
16	8XY5	SUB_V	Subtracts the value in the register Y from the value in register X. Store the value in register X and set the carry flag in register F based on if the operation underflowed or overflowed.
17	8XY6	SING_RSHIFT	Performs a single right shift on the value in register X.
18	``