.
├── oscar64/        # Oscar64 cross-compiler (git submodule)
├── docs/c64/       # Low-level C64 reference (memory map, VIC, CIA, SID, …)
├── src/            # Your C code
│   ├── helloworld.c
│   └── build.sh    # Compile + run helper
├── OSCAR64.md      # Notes on the Oscar64 compiler internals
└── PROG_C64.md     # Notes on programming the C64 hardware

First-time setup

# 1. Clone with submodules:
git clone --recurse-submodules <this-repo-url>

# Or, if you already cloned without --recurse-submodules:
git submodule update --init --recursive

Building

cd src
./build.sh            # compile helloworld.c → src/build/helloworld.prg
./build.sh -e         # compile, then run in oscar64's built-in emulator

build.sh will build the oscar64 compiler automatically the first time (it runs make -C make compiler inside ./oscar64/ if ./oscar64/bin/oscar64 doesn't exist yet).

To run the resulting .prg on a real C64 or in VICE:

x64 src/build/helloworld.prg

Documentation

PROG_C64.md — how the C64 hardware actually works, from a low-level programming perspective. Start here if you want to understand what's going on under the hood.
OSCAR64.md — how the Oscar64 compiler works internally, plus a C64- specific section on how to use it well (memory model, bank switching, raster IRQs, common mistakes).
docs/c64/ — downloaded reference material: the full Commodore 64 Programmer's Reference Guide text, Christian Bauer's canonical VIC-II paper, and per-chip reference notes.