usbd: Add midi interface definition from @paulhamsh.

Taken from https://github.com/paulhamsh/Micropython-Midi-Device
as of commit 2678d13.

micropython/usbd/midi.py

@@ -0,0 +1,265 @@
+# MicroPython USB MIDI module
+# MIT license; Copyright (c) 2022 Angus Gratton, Paul Hamshere
+from device import USBInterface
+from micropython import const
+import ustruct
+
+dat = bytearray(64)
+
+_INTERFACE_CLASS_IGNORE = 0x01
+_INTERFACE_SUBCLASS_IGNORE = 0x01
+_PROTOCOL_IGNORE = 0x00
+
+
+class RingBuf:
+    def __init__(self, size):
+        self.data = bytearray(size)
+        self.size = size
+        self.index_put = 0
+        self.index_get = 0
+
+    def put(self, value):
+        next_index = (self.index_put + 1) % self.size
+        # check for overflow
+        if self.index_get != next_index: 
+            self.data[self.index_put] = value
+            self.index_put = next_index
+            return value
+        else:
+            return None
+
+    def get(self):
+        if self.index_get == self.index_put:
+            return None  ## buffer empty
+        else:
+            value = self.data[self.index_get]
+            self.index_get = (self.index_get + 1) % self.size
+            return value
+
+    def is_empty(self):
+        return (self.index_get == self. index_put)
+
+
+class AudioInterface(USBInterface):
+    """ Abstract base class to implement a USB MIDI device in Python. """
+    def __init__(self):
+        super().__init__(
+            _INTERFACE_CLASS_IGNORE, _INTERFACE_SUBCLASS_IGNORE, _PROTOCOL_IGNORE, 0x00
+        )
+
+
+    def get_itf_descriptor(self, num_eps, itf_idx, str_idx):
+        """Return the MIDI USB interface descriptors.
+        """
+
+        ms_interface = ustruct.pack(
+            "<BBBBBBBBB",
+            9,        # bLength
+            0x04,     # bDescriptorType INTERFACE
+            itf_idx,  # bInterfaceNumber
+            0x00,     # bAlternateSetting
+            0x00,     # bNumEndpoints
+            0x01,     # bInterfaceClass AUDIO
+            0x01,     # bInterfaceSubclass AUDIO_CONTROL
+            0x00,     # bInterfaceProtocol
+            0x00      # iInterface
+        )
+        cs_ms_interface = ustruct.pack(
+            "<BBBHHBB",
+            9,      # bLength
+            0x24,   # bDescriptorType CS_INTERFACE
+            0x01,   # bDescriptorSubtype MS_HEADER
+            0x0100, # BcdADC
+            0x0009, # wTotalLength
+            0x01,   # bInCollection,
+            0x01    # baInterfaceNr
+        )
+
+        iface =  ms_interface + cs_ms_interface    
+        return (iface, [])
+        #return (b"", [])
+
+
+class MIDIInterface(USBInterface):
+    """ Base class to implement a USB MIDI device in Python. """
+    def __init__(self):
+        super().__init__(
+            _INTERFACE_CLASS_IGNORE, _INTERFACE_SUBCLASS_IGNORE, _PROTOCOL_IGNORE, 0x00
+        )
+        self.ep_out = 0x03  # set during enumeration
+        self.ep_in = 0x83
+        self.got_data = False
+        self.rx_data = bytearray(64)
+        self.rb = RingBuf(128)
+
+
+    def send_data(self, tx_data):
+        """ Helper function to send data. """
+        self.submit_xfer(0x83, tx_data)
+
+    def midi_received(self):
+        return not self.rb.is_empty()
+
+    def get_rb(self):
+        return self.rb.get()
+
+    def receive_data_callback(self, ep_addr, result, xferred_bytes):
+        for i in range (0, xferred_bytes):
+            self.rb.put(self.rx_data[i])
+        self.submit_xfer(0x03, self.rx_data, self.receive_data_callback)       
+
+    def start_receive_data(self):
+        self.submit_xfer(0x03, self.rx_data, self.receive_data_callback) # self.receive_data_callback)
+
+    def get_itf_descriptor(self, num_eps, itf_idx, str_idx):
+        """Return the MIDI USB interface descriptors.  """
+
+        ms_interface = ustruct.pack(
+            "<BBBBBBBBB",
+            9,        # bLength
+            0x04,     # bDescriptorType INTERFACE
+            itf_idx,  # bInterfaceNumber
+            0x00,     # bAlternateSetting
+            0x02,     # bNumEndpoints
+            0x01,     # bInterfaceClass AUDIO
+            0x03,     # bInterfaceSubclass MIDISTREAMING
+            0x00,     # bInterfaceProtocol
+            0x00      # iInterface
+        )
+        cs_ms_interface = ustruct.pack(
+            "<BBBHH",
+            7,      # bLength
+            0x24,   # bDescriptorType CS_INTERFACE
+            0x01,   # bDescriptorSubtype MS_HEADER
+            0x0100, # BcdADC
+            0x0041  # wTotalLength
+        )
+
+        jack1 = ustruct.pack(
+            "<BBBBBB",
+            6,     # bLength
+            0x24,  # bDescriptorType CS_INTERFACE
+            0x02,  # bDescriptorSubtype MIDI_IN_JACK
+            0x01,  # bJackType EMBEDDED
+            0x01,  # bJackID
+            0x00   # iJack
+        )
+        jack2 = ustruct.pack(
+            "<BBBBBB",
+            6,     # bLength
+            0x24,  # bDescriptorType CS_INTERFACE
+            0x02,  # bDescriptorSubtype MIDI_IN_JACK
+            0x02,  # bJackType EXTERNAL
+            0x02,  # bJackID
+            0x00   # iJack
+        )
+        jack3 = ustruct.pack(
+            "<BBBBBBBBB",
+            9,     # bLength
+            0x24,  # bDescriptorType CS_INTERFACE
+            0x03,  # bDescriptorSubtype MIDI_OUT_JACK
+            0x01,  # bJackType EMBEDDED
+            0x03,  # bJackID
+            0x01,  # bNrInputPins
+            0x02,  # BaSourceID
+            0x01,  # BaSourcePin
+            0x00   # iJack
+        ) 
+        jack4 = ustruct.pack(
+            "<BBBBBBBBB",
+            9,     # bLength
+            0x24,  # bDescriptorType CS_INTERFACE
+            0x03,  # bDescriptorSubtype MIDI_OUT_JACK
+            0x02,  # bJackType EXTERNAL
+            0x04,  # bJackID
+            0x01,  # bNrInputPins
+            0x01,  # BaSourceID
+            0x01,  # BaSourcePin
+            0x00   # iJack
+        )
+        iface =  ms_interface + cs_ms_interface + jack1 + jack2 + jack3 + jack4
+        return (iface, [])
+
+    def get_endpoint_descriptors(self, ep_addr, str_idx):
+        """Return the MIDI USB endpoint descriptors.
+        """
+
+        epA = ustruct.pack(
+            "<BBBBHBBB",
+            9,      # bLength
+            0x05,   # bDescriptorType ENDPOINT
+            0x03,   # bEndpointAddress 
+            0x02,   # bmAttributes
+            0x0040, # wMaxPacketSize
+            0x00,   # bInterval
+            0x00,   # bRefresh
+            0x00    # bSyncAddress
+        )
+        cs_epA = ustruct.pack(
+            "<BBBBB",
+            5,     # bLength
+            0x25,  # bDescriptorType CS_ENDPOINT
+            0x01,  # bDescriptorSubtype MS_GENERAL
+            0x01,  # bNumEmbMIDIJack
+            0x01   # BaAssocJackID
+        )
+        epB = ustruct.pack(
+            "<BBBBHBBB",
+            9,      # bLength
+            0x05,   # bDescriptorType ENDPOINT
+            0x83,   # bEndpointAddress 
+            0x02,   # bmAttributes
+            0x0040, # wMaxPacketSize
+            0x00,   # bInterval
+            0x00,   # bRefresh
+            0x00    # bSyncAddress
+        )
+        cs_epB = ustruct.pack(
+            "<BBBBB",
+            5,     # bLength
+            0x25,  # bDescriptorType CS_ENDPOINT
+            0x01,  # bDescriptorSubtype MS_GENERAL
+            0x01,  # bNumEmbMIDIJack
+            0x03   # BaAssocJackID
+        )    
+
+        desc = epA + cs_epA + epB + cs_epB
+        ep_addr = [0x03, 0x83]
+        return (desc, [], ep_addr)
+
+
+class AudioUSB(AudioInterface):
+    """ Empty USB Audio interface """
+    def __init__(self):
+        super().__init__()
+
+class MidiUSB(MIDIInterface):
+    """ Very basic synchronous USB MIDI interface """
+    def __init__(self):
+        super().__init__()
+
+    def note_on(self, channel, pitch, vel):
+        obuf = ustruct.pack("<BBBB", 0x09, 0x90 | channel, pitch, vel)
+        super().send_data(obuf)
+
+    def note_off(self, channel, pitch, vel):
+        obuf = ustruct.pack("<BBBB", 0x08, 0x80 | channel, pitch, vel)
+        super().send_data(obuf)     
+
+    def start(self):
+        super().start_receive_data()
+
+    def midi_received(self):
+        return super().midi_received()
+
+    def get_midi(self):
+        if super().midi_received():
+            cin = super().get_rb()
+            cmd = super().get_rb()
+            val1 = super().get_rb()
+            val2 = super().get_rb()
+            return (cin, cmd, val1, val2)
+        else:
+            return (None, None, None, None)
+
+