3 * <http://bugs.libre-riscv.org/show_bug.cgi?id=3>
4 * <https://github.com/skristiansson/i2s>
5 * <https://en.wikipedia.org/wiki/I%C2%B2S>
7 Question: how does I2S do 4-wire output?
11 * <https://opencores.org/project,ac97>
12 * <https://en.wikipedia.org/wiki/AC%2797>
14 Question: how does AC97 fit in with I2S?