usb: add support for midi

src/machine/usb/midi/buffer.go

@@ -0,0 +1,52 @@
+package midi
+
+import (
+	"runtime/volatile"
+)
+
+const bufferSize = 128
+
+// RingBuffer is ring buffer implementation inspired by post at
+// https://www.embeddedrelated.com/showthread/comp.arch.embedded/77084-1.php
+type RingBuffer struct {
+	rxbuffer [bufferSize][4]byte
+	head     volatile.Register8
+	tail     volatile.Register8
+}
+
+// NewRingBuffer returns a new ring buffer.
+func NewRingBuffer() *RingBuffer {
+	return &RingBuffer{}
+}
+
+// Used returns how many bytes in buffer have been used.
+func (rb *RingBuffer) Used() uint8 {
+	return uint8(rb.head.Get() - rb.tail.Get())
+}
+
+// Put stores a byte in the buffer. If the buffer is already
+// full, the method will return false.
+func (rb *RingBuffer) Put(val []byte) bool {
+	if rb.Used() != bufferSize {
+		rb.head.Set(rb.head.Get() + 1)
+		copy(rb.rxbuffer[rb.head.Get()%bufferSize][:], val)
+		return true
+	}
+	return false
+}
+
+// Get returns a byte from the buffer. If the buffer is empty,
+// the method will return a false as the second value.
+func (rb *RingBuffer) Get() ([]byte, bool) {
+	if rb.Used() != 0 {
+		rb.tail.Set(rb.tail.Get() + 1)
+		return rb.rxbuffer[rb.tail.Get()%bufferSize][:], true
+	}
+	return nil, false
+}
+
+// Clear resets the head and tail pointer to zero.
+func (rb *RingBuffer) Clear() {
+	rb.head.Set(0)
+	rb.tail.Set(0)
+}

src/machine/usb/midi/midi.go

@@ -0,0 +1,79 @@
+package midi
+
+import (
+	"machine"
+)
+
+const (
+	midiEndpointOut = 5 // from PC
+	midiEndpointIn  = 6 // to PC
+)
+
+var Midi *midi
+
+type midi struct {
+	buf            *RingBuffer
+	callbackFuncRx func([]byte)
+	waitTxc        bool
+}
+
+func init() {
+	if Midi == nil {
+		Midi = newMidi()
+	}
+}
+
+// New returns hid-mouse.
+func New() *midi {
+	return Midi
+}
+
+func newMidi() *midi {
+	m := &midi{
+		buf: NewRingBuffer(),
+	}
+	machine.EnableMIDI(m.Callback, m.CallbackRx, nil)
+	return m
+}
+
+func (m *midi) SetCallback(callbackRx func([]byte)) {
+	m.callbackFuncRx = callbackRx
+}
+
+func (m *midi) Write(b []byte) (n int, err error) {
+	i := 0
+	for i = 0; i < len(b); i += 4 {
+		m.tx(b[i : i+4])
+	}
+	return i, nil
+}
+
+// sendUSBPacket sends a MIDIPacket.
+func (m *midi) sendUSBPacket(b []byte) {
+	machine.SendUSBInPacket(midiEndpointIn, b)
+}
+
+// from BulkIn
+func (m *midi) Callback() {
+	m.waitTxc = false
+	if b, ok := m.buf.Get(); ok {
+		m.waitTxc = true
+		m.sendUSBPacket(b)
+	}
+}
+
+func (m *midi) tx(b []byte) {
+	if m.waitTxc {
+		m.buf.Put(b)
+	} else {
+		m.waitTxc = true
+		m.sendUSBPacket(b)
+	}
+}
+
+// from BulkOut
+func (m *midi) CallbackRx(b []byte) {
+	if m.callbackFuncRx != nil {
+		m.callbackFuncRx(b)
+	}
+}