JimKnowler/SpaceInvaders8080

Software Emulation of Intel 8080 CPU for Taito Space Invaders Arcade Game

Space Invaders Arcade Emulator

Emulate Intel 8080 CPU + Taito Space Invaders machine Hardware.

Requirements

• Windows 10

• Visual Studio 2019 (tested with free 'community' edition) https://visualstudio.microsoft.com/downloads/

References

• Using the OLC Pixel Game Engine for 2D UI https://github.com/OneLoneCoder/olcPixelGameEngine

• Implemented while following 8080 guide on emulator101 http://emulator101.com/

• Information on SpaceInvaders hardware http://computerarcheology.com/Arcade/SpaceInvaders/Hardware.html

• 8080 Chipset opcodes http://www.emulator101.com/reference/8080-by-opcode.html

• 8080 Programmers Reference https://altairclone.com/downloads/manuals/8080%20Programmers%20Manual.pdf

CPU Diagnostics

To run the 8080 cpu diagnostic tests, enable the macro 'CPUDIAG' in BuildOptions.h.

When the test is successful you should see a message in console TTY saying "CPU IS OPERATIONAL".

Space Invaders

By default, the emulator will run the original Taito Space Invaders ROM.

Instructions

The emulator starts in Debugger mode where you can step through opcodes, executing them one at a time.

The emulator can be switched into Run mode, where it will simulate running a Taito Space Invaders machine.

Key	Purpose
R	Switch to RUN mode
D	Switch to DEBUGGER mode

DEBUGGER Mode

Key	Purpose
SPACE	Step through 1 opcode
SHIFT+SPACE	Step through 10 opcodes
CTRL+SHIFT+SPACE	Step through 100 opcodes

RUN Mode

Key	Purpose
C	Coin
1	Start 1 player
2	Start 2 player
LEFT CURSOR	Player 1 - Move Left
RIGHT CURSOR	Player 1 - Move Right
SPACE	Player 1 - Fire
Z	Player 2 - Move Left
X	Player 2 - Move Right
SHIFT	Player 2 - Fire

Debugging Tools

The CPU emulation supports setting breakpoints for:

• Executing Opcode at a specified address
• Writing to memory at a specified address

Multiple breakpoints can be instantiated.

Status

Progress

• Space Invaders Game is fully playable!
• Player is able to insert coins + start a game
• Player is able to move left/right + fire
• Aliens are able to animate, move left/right + fire
• Player score is incrementing, hi-scores are recorded

Issues

• CPU emulation is not cycle accurate
  • Not currently required for Space Invaders simulation
  • Would be required
  • Would be useful for optimisation (i.e. only simulate 'n' clock cycles per frame)

More Debugging Ideas

• support time travel debugging - the ability to roll forward/backwards in time through CPU + memory state
• support hardware breakpoints
  • when using OUT/IN on specific port, with specific value of A register

Optimisation Ideas

• convert opcode switch to jump tables for O(1) execution