A modular Intel 8080 CPU emulator written in modern C++20, with basic CP/M BDOS support.

Features

• Full 8080 instruction set — all documented opcodes including DAA, rotate group, and the complete conditional branch/call/return matrix
• Accurate flag logic — Sign, Zero, Parity, Carry and Auxiliary Carry updated per instruction per the Intel 8080 datasheet
• 64 KB address space backed by std::array<uint8_t, 0x10000>
• Pluggable I/O bus — wire IN/OUT ports to any peripheral via std::function callbacks
• CP/M BDOS hook — supports function 2 (character output) and function 9 (string output), enough to run standard .COM programs
• Returns clock-cycle counts from Step8080 for future timing/throttling

Repository layout

Native8080/
├── src/
│   ├── cpu8080.h       # State8080 struct, IOBus, public API
│   ├── cpu8080.cpp     # Fetch-Decode-Execute engine
│   └── main.cpp        # CP/M loader and main loop
├── samples/
│   └── hello.com       # Pre-built CP/M Hello World (generated)
├── docs/
│   └── instruction_set_8080.txt  # Opcode reference used during development
├── CMakeLists.txt
└── LICENSE

Building

Requirements: CMake ≥ 3.16, a C++20-capable compiler (GCC 10+, Clang 12+).

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build

The binary is placed at build/native8080.

A Debug build automatically enables -fsanitize=address,undefined when the compiler supports it:

cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug
cmake --build build

Running

# Standard CP/M .COM program (loaded at 0x0100)
./build/native8080 samples/hello.com

# ROM image loaded at a custom address (hex)
./build/native8080 rom.bin 0000

The emulator prints diagnostic messages to stderr and program output to stdout, so they can be separated:

./build/native8080 samples/hello.com 2>/dev/null

CP/M compatibility

The emulator installs a minimal BDOS shim:

C register	Function	Behaviour
2	Console character output	Prints the character in E
9	Print string	Prints from [DE] until $

A RET is placed at 0x0005 and a HLT at 0x0000, so programs that jump to the warm-boot vector exit cleanly.

Extending I/O

Edit make_io_bus() in src/main.cpp to attach real devices:

io.out_handler = [](uint8_t port, uint8_t val) {
    if (port == 0x01) my_uart_write(val);
};
io.in_handler = [](uint8_t port) -> uint8_t {
    if (port == 0x01) return my_uart_read();
    return 0xFF;
};

License

See LICENSE.