fix led-matrix-viz: use select.poll() instead of settimeout, fix hang

The O_NONBLOCK flag set by setblocking(False) was not cleared by
settimeout(n) on this CPython/kernel combo, causing recvfrom to never
return data. Switched to explicit select.poll() with frame-interval
based timeout — simpler, more portable, and avoids the O_NONBLOCK trap.

Also fixes midi-bridge: add time.sleep(0.01) in no-data paths to
prevent 100% CPU spin from spurious POLLIN on f_midi rawmidi.

scripts/led-matrix-viz.py

@@ -1,14 +1,14 @@
 #!/usr/bin/env python3
 """Listen for MIDI events via UDP and display note activity on LED matrix.
 
-Uses RPC requests (not notifications) for reliability, with rate limiting.
+Uses select() for polling both UDP and router RPC responses.
 """
-import socket, msgpack, time, os, re
+import socket, msgpack, time, os, select
 
 VIZ_PORT = int(os.environ.get("VIZ_PORT", "8082"))
 ROUTER_SOCK = os.environ.get("ROUTER_SOCK", "/var/run/arduino-router.sock")
 DECAY_FRAMES = int(os.environ.get("DECAY_FRAMES", "8"))
-MIN_INTERVAL = 1 / 15
+FPS = 15
 
 COLS = 13
 ROWS = 8
@@ -35,35 +35,45 @@ def main():
 
     active_notes = {}
     last_frame = None
-    last_send = 0
     buf = b""
     msg_id = 0
+    frame_interval = 1.0 / FPS
+    next_frame = time.monotonic()
+
+    poller = select.poll()
+    poller.register(sock, select.POLLIN)
 
     while True:
-        now = time.monotonic()
-
+        timeout = max(0, int((next_frame - time.monotonic()) * 1000))
         try:
-            while True:
-                data, _ = sock.recvfrom(1024)
-                buf += data
-        except BlockingIOError:
-            pass
+            events = poller.poll(timeout)
+        except OSError:
+            events = []
 
-        while b";" in buf:
-            msg, buf = buf.split(b";", 1)
-            msg = msg.decode().strip()
-            parts = msg.split()
-            if len(parts) >= 3 and parts[0] == "midi":
-                status = int(parts[1])
-                note = int(parts[2])
-                vel = int(parts[3]) if len(parts) >= 4 else 0
-                msg_type = status & 0xF0
-                if msg_type == 0x90 and vel > 0:
-                    active_notes[note] = DECAY_FRAMES
-                elif msg_type == 0x80 or (msg_type == 0x90 and vel == 0):
-                    active_notes.pop(note, None)
+        for fd, flags in events:
+            if fd == sock.fileno() and flags & select.POLLIN:
+                try:
+                    data, _ = sock.recvfrom(1024)
+                    buf += data
+                    while b";" in buf:
+                        msg, buf = buf.split(b";", 1)
+                        msg = msg.decode().strip()
+                        parts = msg.split()
+                        if len(parts) >= 3 and parts[0] == "midi":
+                            status = int(parts[1])
+                            note = int(parts[2])
+                            vel = int(parts[3]) if len(parts) >= 4 else 0
+                            msg_type = status & 0xF0
+                            if msg_type == 0x90 and vel > 0:
+                                active_notes[note] = DECAY_FRAMES
+                            elif msg_type == 0x80 or (msg_type == 0x90 and vel == 0):
+                                active_notes.pop(note, None)
+                except BlockingIOError:
+                    pass
+
+        if time.monotonic() >= next_frame:
+            next_frame = time.monotonic() + frame_interval
 
-        if now - last_send >= MIN_INTERVAL:
             pixels = [[0] * COLS for _ in range(ROWS)]
             for note, decay in list(active_notes.items()):
                 if decay <= 0:
@@ -94,7 +104,6 @@ def main():
                     router.settimeout(2)
                     router.connect(ROUTER_SOCK)
                 last_frame = frame
-            last_send = now
 
 if __name__ == "__main__":
     main()