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Emulating the YM2612: Part 1 – Interface
This is the first post in a series on emulating the main Sega Genesis sound chip, the Yamaha YM2612 FM synthesis chip, also known as the OPN2. To date, the YM2612 is pretty easily the most difficult-to-emulate sound chip that I have worked on.
I attempted to overview how Yamaha FM synthesis works at a very high level in a section of my previous post on Konami’s VRC7 mapper for the Famicom. The chip also includes a number of features beyond the FM synthesis operators themselves: a low frequency oscillator (LFO) used to power vibrato and tremolo effects, two hardware timers for use by software, and a DAC channel that outputs raw 8-bit PCM samples if enabled. Busy flag behavior doesn’t seem to be completely consistent between different model consoles, and it probably also depends on when exactly the register write occurs within the chip’s internal cycling between channels and operators.
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