FroNES (W.I.P.)

An NES emulator written in C++23 using coroutines.

Roadmap

At the moment I'm implementing the NMOS 6502 which served as the base for the Ricoh 2A03 used in the NES. The reason why I didn't directly start with the actual processor used is because there is a lot more documentation available for the former in contrast to the latter. Once I verify the emulators accuracy (by using available test programs, among others Klaus2m5's test suite), I will look into how I'd need to modify it in order to model the 2A03. Afterwards, I will move on to the next big step; the PPU.

Dependencies

• SDL3 - Core functionality (entry point, system events, input, windowing, etc.)
• Dear ImGui - GUI
• nativefiledialog-extended - Program loading

Those are managed through my custom vcpkg fork and will be automatically installed during the configuration process.

Quickstart

Prerequisites

• C++23 compatible compiler
• The latest stable version of Ninja
• CMake 3.15 or higher

Cloning

Clone the repository with the --recursive flag. This will cause the vcpkg submodule to also be pulled:

git clone https://github.com/Froncu/Fronge --recursive

Configuring & Building

The project includes CMake presets (CMakePresets.json) that configure vcpkg integration automatically. You can configure and build using your preferred IDE or command line.

Note: If creating custom configure/build presets, ensure they inherit from/set configurePreset to the provided default preset to maintain proper vcpkg integration.

Usage

The emulator's windows is split up in 2 main sections:

• Memory
  • There is an overview of the entire memory available. You can scroll or use the "Jump to address" input box to navigate to a desired location. Additionally, there are inputs for controlling both the amount of bytes per row and the amount of visible rows.
  • Most importantly, "Select program" will invoke the platform-native file open dialog and allow you to select a binary program to load into the emulator. "Load address" allows specifying where the load should take place in memory.
• CPU
  • You can view the state of any of the processor's registers.
  • You can set the "Program counter" to a desired value. By default, when the 6502 resets, it loads the value stored in the RESET vector (0xFFFC - 0xFFFD) into the program counter. However, some programs use this (and/or other) vector(s) for other purposes. For example, the Klaus2m5's functional test uses the NMI, RESET and IRQ/BRK vectors as traps for unexpected behaviour and instead expects you to set the program counter to the correct address. Reason why I allow for this.
  • There is some basic execution control available:
    • Tick will execute 1 cycle
    • The tick repeatedly switch will resume/pause the emulation
    • Step will execute as many cycles as are needed to execute the current instruction
    • Reset will trigger a reset