auto-detect MIDI device, drop ALSA sequencer dependency, MPK Mini simulator

midi-bridge.py:
  - Auto-detect rawmidi device (gadget f_midi > env override > fallback)
  - Reconnect on ENODEV (device hotplug)
  - No longer needs MIDI_BRIDGE_DEV env var in common cases

start-synth.sh:
  - Remove all -alsamidi/-midiadddev flags (kernel lacks CONFIG_SND_SEQUENCER)
  - MIDI handled entirely by midi-bridge.service → UDP → netreceive
  - Host mode: same approach, no ALSA sequencer needed

mpk-mini-sim.pd:
  - New MPK Mini Mk II simulator (25 keys, 8 pads, 8 CC knobs)
  - Proper Pd #X obj format for all objects (bng, hsl, t, del, netsend, loadbang)
  - UDP output to board:8081, matching midi-bridge format

system: enable usb-gadget-audio.service at boot, load dwc3 module at boot

scripts/midi-bridge.py

@@ -1,76 +1,102 @@
 #!/usr/bin/env python3
-"""Bridge raw MIDI device to Pd via UDP. For host mode with MPK Mini.
+"""Bridge raw MIDI device to Pd via UDP. Auto-detects gadget vs host mode.
 
 Sends parsed MIDI messages as Pd-style 'midi status data1 data2;' strings
 to UDP ports for Pd (8081) and LED matrix visualization (8082).
 """
-import os, socket, time, select, struct
+import os, socket, time, select, pathlib
 
-MIDI_DEV = os.environ.get("MIDI_BRIDGE_DEV", "/dev/snd/midiC0D0")
 PD_HOST = os.environ.get("MIDI_BRIDGE_HOST", "127.0.0.1")
 PD_PORT = int(os.environ.get("MIDI_BRIDGE_PORT", "8081"))
 VIZ_PORT = int(os.environ.get("VIZ_PORT", "8082"))
 
+def _find_midi_dev():
+    """Auto-detect rawmidi device. Preference: gadget f_midi > env override > host mode."""
+    dev = os.environ.get("MIDI_BRIDGE_DEV")
+    if dev:
+        return dev
+    # Look for gadget f_midi card first
+    cards = pathlib.Path("/proc/asound").glob("card*")
+    for card_dir in cards:
+        cmi = card_dir / "id"
+        if cmi.exists() and "midi" in cmi.read_text().strip():
+            card_num = card_dir.name.replace("card", "")
+            midi_dev = f"/dev/snd/midiC{card_num}D0"
+            if os.path.exists(midi_dev):
+                return midi_dev
+    # Fallback: any rawmidi device
+    rawdevs = sorted(pathlib.Path("/dev/snd").glob("midiC?D0"))
+    if rawdevs:
+        return str(rawdevs[0])
+    return "/dev/snd/midiC0D0"  # fallback for host mode
+
 def midi_msg(status, data1, data2=None):
     if data2 is not None:
         return f"midi {status} {data1} {data2};"
     return f"midi {status} {data1};"
 
-def main():
-    while not os.path.exists(MIDI_DEV):
+def _open_midi():
+    midi_dev = _find_midi_dev()
+    while not os.path.exists(midi_dev):
         time.sleep(0.5)
-
-    fd = os.open(MIDI_DEV, os.O_RDWR | os.O_NONBLOCK)
+        midi_dev = _find_midi_dev()
+    fd = os.open(midi_dev, os.O_RDWR | os.O_NONBLOCK)
     os.set_blocking(fd, False)
-    poll = select.poll()
-    poll.register(fd, select.POLLIN)
+    return fd
 
+def main():
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
 
     running = True
-    buf = bytearray()
     while running:
         try:
-            events = poll.poll(500)
-            for f, flags in events:
-                if flags & select.POLLIN:
-                    data = os.read(fd, 1024)
-                    if not data:
-                        continue
-                    for byte in data:
-                        if byte & 0x80:
-                            if len(buf) > 0 and buf[0] >= 0x80:
-                                _flush(sock, buf, PD_HOST, PD_PORT, VIZ_PORT)
-                            buf = bytearray([byte])
-                        else:
-                            buf.append(byte)
-                            if len(buf) >= 3 and (buf[0] & 0xE0) in (0x80, 0x90, 0xA0, 0xB0, 0xE0):
-                                _flush(sock, buf, PD_HOST, PD_PORT, VIZ_PORT)
-                                buf = bytearray()
-                            elif len(buf) >= 2 and (buf[0] & 0xE0) in (0xC0, 0xD0):
-                                _flush(sock, buf, PD_HOST, PD_PORT, VIZ_PORT)
-                                buf = bytearray()
-        except (BlockingIOError, OSError) as e:
-            if isinstance(e, OSError) and e.errno == 19:
-                time.sleep(1)
-                continue
-            if not isinstance(e, BlockingIOError):
-                raise
+            fd = _open_midi()
+            poll = select.poll()
+            poll.register(fd, select.POLLIN)
+            buf = bytearray()
+            while running:
+                try:
+                    events = poll.poll(500)
+                    for f, flags in events:
+                        if flags & select.POLLIN:
+                            data = os.read(fd, 1024)
+                            if not data:
+                                continue
+                            for byte in data:
+                                if byte & 0x80:
+                                    if len(buf) > 0 and buf[0] >= 0x80:
+                                        _flush(sock, buf)
+                                    buf = bytearray([byte])
+                                else:
+                                    buf.append(byte)
+                                    if len(buf) >= 3 and (buf[0] & 0xE0) in (0x80, 0x90, 0xA0, 0xB0, 0xE0):
+                                        _flush(sock, buf)
+                                        buf = bytearray()
+                                    elif len(buf) >= 2 and (buf[0] & 0xE0) in (0xC0, 0xD0):
+                                        _flush(sock, buf)
+                                        buf = bytearray()
+                except OSError as e:
+                    if e.errno == 19:
+                        os.close(fd)
+                        time.sleep(1)
+                        break
+                    raise
+                except BlockingIOError:
+                    pass
         except KeyboardInterrupt:
             running = False
 
-    os.close(fd)
     sock.close()
 
-def _flush(sock, buf, pd_host, pd_port, viz_port):
+def _flush(sock, buf):
     status = buf[0]
     if (buf[0] & 0xF0) == 0xF0:
         return
     data1 = buf[1]
     data2 = buf[2] if len(buf) >= 3 else None
     msg = midi_msg(status, data1, data2)
-    sock.sendto(msg.encode(), (pd_host, pd_port))
-    sock.sendto(msg.encode(), (pd_host, viz_port))
+    sock.sendto(msg.encode(), (PD_HOST, PD_PORT))
+    sock.sendto(msg.encode(), (PD_HOST, VIZ_PORT))
 
 if __name__ == "__main__":
     main()