Extracting the judge
When I rewrote cable-club, the first thing I built was not the CPU or the renderer. It was the test harness. An emulator without accuracy tests is a program that produces plausible-looking output with no way to know if it is correct. I had already learned that lesson once. What accuracy testing means A GBA emulator can pass every standard CPU test suite — every ARM instruction, every Thumb instruction, every edge case in isolation — and still produce the wrong output when running a real game. The test suites verify that individual instructions behave correctly. They do not verify that the CPU, memory bus, DMA controller, interrupt system, and PPU all interact correctly over thousands of frames. ...