Module apu 

The four sound channels and the mixer.

Each channel has a configuration type: Pulse for channels 1 and 2, Wave for channel 3, Noise for channel 4. Building one is a chain of const methods, and play writes it out and starts the channel.

const JUMP: Pulse = Pulse::new(12).note(Note::C, 5).length(8);

JUMP.play_ch2();

A sound played from one place belongs in a constant. A set of them played from the same place belongs in a table.

See https://gbdev.io/pandocs/Audio.html.

Power

The boot ROM leaves the APU on at full volume. A program that only wants sound has nothing to set up. It does leave channels 3 and 4 reaching the left output alone, which set_panning settles.

power_off draws less current and is worth having on a pause screen; power_on comes back from it.

Writing to DIV

Envelopes, length timers and the channel 1 sweep are all counted off DIV, so timer::reset_divider steps them early. Resetting it while sound is playing is audible.

Structs

Noise

Channel 4’s settings.

Pulse

A pulse channel’s settings.

Wave

Channel 3’s settings, which play whatever load_wave last put in wave RAM.

Enums

Channel

One of the four sound channels.

Note

One of the twelve semitones.

Functions

load_wave

Load the 32 four-bit samples channel 3 plays, high nibble of each byte first.

outputcgb

What a channel is putting out, from 0 to 15.

playing

Whether a channel is still running.

power_off

Power the APU off.

power_on

Power the APU on.

set_master

Set the master volume.

set_panning

Set which channels reach which output.

silence

Take a channel down to nothing without stopping it.

stop

Stop a channel by turning its DAC off.