8080_emulator

A simple 8080 emulator made with the goal of emulating space invaders. Based on and inspired by the guide at emulator101.

Launch the emulator

The Space Invader ROM files are omitted due to copyright. To run the emulator, add the invaders.[e,f,g,h] files to the ROM directory at the root of the project.

Compile

gcc -g -O0 8080_main.c -o 8080_main

Run

The emulator takes in an optional parameters for verbosity and to specify the number of instructions to execute.

./8080_main [<verbose>] [<stop_at>]

Notes

Disassembler

Each instruction handler is defined using one of the INSTR macros, which handle the various instruction formats. Then, each instruction handler is added to disasm_handlers, at their respective opcode index.

Emulator

Like the disassembler, the emulation handlers are added to the emu_handlers, indexed by opcode. Common functionalities are moved into seperate functions to avoid code duplication. Unless explicitly mentioned, instructions do not affect flags.

Flags

• Zero: if result of instruction has the value 0, flag is set; otherwise it is reset.
• Sign: if the most significant bit of the result of the operation has value 1, this flag is set; otherwise it is reset.
• Parity: if the module 2 sum of the bits of the result of the operation is 0, (i.e. result has even parity), this flag is set; otherwise it is reset.
• Carry: If the instruction results in a carry (from addition), or a borrow (from subtraction or comparison) out of the high-order bit, this flag is set, otherwise it is reset.
• Auxiliary Carry: If the instruction caused a carry out of bit 3 and into bit 4 of the resulting value, the auxiliary carry is set; otherwise it is reset. This flag is affected by single precision additions, subtractions, increments, decrements, comparisons, and logical operations, but is principally used with additions and increments preceding a DAA (Decimal Adjust Accumulator) instruction.

Goals

• Full 8080 instruction disassembly
• Full 8080 instruction emulation
• Draw graphics
• Proper machine timing (slow down to 2MHz)
  • Use correct number of cycles per instruction
• I/O
  • Shift register hardware (Write ports 2 & 4, Read port 3)
  • Player input
• Sounds

References

Intel 8080 Microcomputer Systems User's Manual, September 1975 ComputerArcheology Space Invaders Hardware Overview