usb/midi: add definition of MIDI note number

src/examples/usb-midi/main.go

@@ -7,6 +7,9 @@ import (
 	"time"
 )
 
+// Try it easily by opening the following site in Chrome.
+// https://www.onlinemusictools.com/kb/
+
 func main() {
 	led := machine.LED
 	led.Configure(machine.PinConfig{Mode: machine.PinOutput})
@@ -24,12 +27,12 @@ func main() {
 	prev := true
 	chords := []struct {
 		name string
-		keys []byte
+		keys []midi.Note
 	}{
-		{name: "C ", keys: []byte{60, 64, 67}},
+		{name: "C ", keys: []midi.Note{midi.C4, midi.E4, midi.G4}},
-		{name: "G ", keys: []byte{55, 59, 62}},
+		{name: "G ", keys: []midi.Note{midi.G3, midi.B3, midi.D4}},
-		{name: "Am", keys: []byte{57, 60, 64}},
+		{name: "Am", keys: []midi.Note{midi.A3, midi.C4, midi.E4}},
-		{name: "F ", keys: []byte{53, 57, 60}},
+		{name: "F ", keys: []midi.Note{midi.F3, midi.A3, midi.C4}},
 	}
 	index := 0
 

src/machine/usb/midi/messages.go

@@ -1,14 +1,14 @@
 package midi
 
 // NoteOn sends a note on message.
-func (m *midi) NoteOn(cable, channel, note, velocity uint8) {
+func (m *midi) NoteOn(cable, channel uint8, note Note, velocity uint8) {
-	m.msg[0], m.msg[1], m.msg[2], m.msg[3] = (cable&0xf<<4)|0x9, 0x90|(channel&0xf), note&0x7f, velocity&0x7f
+	m.msg[0], m.msg[1], m.msg[2], m.msg[3] = (cable&0xf<<4)|0x9, 0x90|(channel&0xf), byte(note)&0x7f, velocity&0x7f
 	m.Write(m.msg[:])
 }
 
 // NoteOff sends a note off message.
-func (m *midi) NoteOff(cable, channel, note, velocity uint8) {
+func (m *midi) NoteOff(cable, channel uint8, note Note, velocity uint8) {
-	m.msg[0], m.msg[1], m.msg[2], m.msg[3] = (cable&0xf<<4)|0x8, 0x80|(channel&0xf), note&0x7f, velocity&0x7f
+	m.msg[0], m.msg[1], m.msg[2], m.msg[3] = (cable&0xf<<4)|0x8, 0x80|(channel&0xf), byte(note)&0x7f, velocity&0x7f
 	m.Write(m.msg[:])
 }
 

src/machine/usb/midi/notes.go

@@ -0,0 +1,108 @@
+package midi
+
+// Note represents a MIDI note number. For example, Note(69) is A4 or 440Hz.
+type Note uint8
+
+// Define all the notes in a format similar to the Tone library in the Arduino
+// IDE.
+const (
+	A0 Note = iota + 21 // 27.5Hz
+	AS0
+	B0
+	C1
+	CS1
+	D1
+	DS1
+	E1
+	F1
+	FS1
+	G1
+	GS1
+	A1 // 55Hz
+	AS1
+	B1
+	C2
+	CS2
+	D2
+	DS2
+	E2
+	F2
+	FS2
+	G2
+	GS2
+	A2 // 110Hz
+	AS2
+	B2
+	C3
+	CS3
+	D3
+	DS3
+	E3
+	F3
+	FS3
+	G3
+	GS3
+	A3 // 220Hz
+	AS3
+	B3
+	C4
+	CS4
+	D4
+	DS4
+	E4
+	F4
+	FS4
+	G4
+	GS4
+	A4 // 440Hz
+	AS4
+	B4
+	C5
+	CS5
+	D5
+	DS5
+	E5
+	F5
+	FS5
+	G5
+	GS5
+	A5 // 880Hz
+	AS5
+	B5
+	C6
+	CS6
+	D6
+	DS6
+	E6
+	F6
+	FS6
+	G6
+	GS6
+	A6 // 1760Hz
+	AS6
+	B6
+	C7
+	CS7
+	D7
+	DS7
+	E7
+	F7
+	FS7
+	G7
+	GS7
+	A7 // 3520Hz
+	AS7
+	B7
+	C8
+	CS8
+	D8
+	DS8
+	E8
+	F8
+	FS8
+	G8
+	GS8
+	A8 // 7040Hz
+	AS8
+	B8
+)