Fix Morse decoder scope events not reaching frontend

Replace blocking rtl_stdout.read() with select()+os.read() so the
decoder thread emits diagnostic heartbeat scope events when rtl_fm
produces no PCM data (common in direct sampling mode). Add waiting-state
rendering in the scope canvas and hide the generic placeholder/status
bar for morse mode.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

static/js/modes/morse.js

@@ -22,6 +22,7 @@ var MorseMode = (function () {
     var SCOPE_HISTORY_LEN = 300;
     var scopeThreshold = 0;
     var scopeToneOn = false;
+    var scopeWaiting = false;
 
     // ---- Initialization ----
 
@@ -150,6 +151,11 @@ var MorseMode = (function () {
         if (type === 'scope') {
             // Update scope data
             var amps = msg.amplitudes || [];
+            if (msg.waiting && amps.length === 0 && scopeHistory.length === 0) {
+                scopeWaiting = true;
+            } else if (amps.length > 0) {
+                scopeWaiting = false;
+            }
             for (var i = 0; i < amps.length; i++) {
                 scopeHistory.push(amps[i]);
                 if (scopeHistory.length > SCOPE_HISTORY_LEN) {
@@ -238,6 +244,7 @@ var MorseMode = (function () {
         scopeCtx = canvas.getContext('2d');
         scopeCtx.scale(dpr, dpr);
         scopeHistory = [];
+        scopeWaiting = false;
 
         var toneLabel = document.getElementById('morseScopeToneLabel');
         var threshLabel = document.getElementById('morseScopeThreshLabel');
@@ -255,6 +262,13 @@ var MorseMode = (function () {
             if (threshLabel) threshLabel.textContent = scopeThreshold > 0 ? Math.round(scopeThreshold) : '--';
 
             if (scopeHistory.length === 0) {
+                if (scopeWaiting) {
+                    scopeCtx.fillStyle = '#556677';
+                    scopeCtx.font = '12px monospace';
+                    scopeCtx.textAlign = 'center';
+                    scopeCtx.fillText('Awaiting SDR data\u2026', w / 2, h / 2);
+                    scopeCtx.textAlign = 'start';
+                }
                 scopeAnim = requestAnimationFrame(draw);
                 return;
             }

templates/index.html

@@ -4256,8 +4256,8 @@
             // Hide output console for modes with their own visualizations
             const outputEl = document.getElementById('output');
             const statusBar = document.querySelector('.status-bar');
-            if (outputEl) outputEl.style.display = (mode === 'satellite' || mode === 'sstv' || mode === 'weathersat' || mode === 'sstv_general' || mode === 'wefax' || mode === 'aprs' || mode === 'wifi' || mode === 'bluetooth' || mode === 'tscm' || mode === 'spystations' || mode === 'meshtastic' || mode === 'websdr' || mode === 'subghz' || mode === 'spaceweather' || mode === 'bt_locate' || mode === 'waterfall') ? 'none' : 'block';
-            if (statusBar) statusBar.style.display = (mode === 'satellite' || mode === 'websdr' || mode === 'subghz' || mode === 'spaceweather' || mode === 'waterfall') ? 'none' : 'flex';
+            if (outputEl) outputEl.style.display = (mode === 'satellite' || mode === 'sstv' || mode === 'weathersat' || mode === 'sstv_general' || mode === 'wefax' || mode === 'aprs' || mode === 'wifi' || mode === 'bluetooth' || mode === 'tscm' || mode === 'spystations' || mode === 'meshtastic' || mode === 'websdr' || mode === 'subghz' || mode === 'spaceweather' || mode === 'bt_locate' || mode === 'waterfall' || mode === 'morse') ? 'none' : 'block';
+            if (statusBar) statusBar.style.display = (mode === 'satellite' || mode === 'websdr' || mode === 'subghz' || mode === 'spaceweather' || mode === 'waterfall' || mode === 'morse') ? 'none' : 'flex';
 
             // Restore sidebar when leaving Meshtastic mode (user may have collapsed it)
             if (mode !== 'meshtastic') {

tests/test_morse.py

@@ -327,6 +327,48 @@ class TestMorseDecoderThread:
         t.join(timeout=5)
         assert not t.is_alive(), "Thread should finish after reading all data"
 
+    def test_thread_heartbeat_on_no_data(self):
+        """When rtl_fm produces no data, thread should emit waiting scope events."""
+        import os as _os
+        stop = threading.Event()
+        q = queue.Queue(maxsize=100)
+
+        # Create a pipe that never gets written to (simulates rtl_fm with no output)
+        read_fd, write_fd = _os.pipe()
+        read_file = _os.fdopen(read_fd, 'rb', 0)
+
+        t = threading.Thread(
+            target=morse_decoder_thread,
+            args=(read_file, q, stop),
+        )
+        t.daemon = True
+        t.start()
+
+        # Wait up to 5 seconds for at least one heartbeat event
+        events = []
+        import time as _time
+        deadline = _time.monotonic() + 5.0
+        while _time.monotonic() < deadline:
+            try:
+                ev = q.get(timeout=0.5)
+                events.append(ev)
+                if ev.get('waiting'):
+                    break
+            except queue.Empty:
+                continue
+
+        stop.set()
+        _os.close(write_fd)
+        read_file.close()
+        t.join(timeout=3)
+
+        waiting_events = [e for e in events if e.get('type') == 'scope' and e.get('waiting')]
+        assert len(waiting_events) >= 1, f"Expected waiting heartbeat events, got {events}"
+        ev = waiting_events[0]
+        assert ev['amplitudes'] == []
+        assert ev['threshold'] == 0
+        assert ev['tone_on'] is False
+
     def test_thread_produces_events(self):
         """Thread should push character events to the queue."""
         import io

utils/morse.py

@@ -7,7 +7,9 @@ from __future__ import annotations
 
 import contextlib
 import math
+import os
 import queue
+import select
 import struct
 import threading
 import time
@@ -284,8 +286,26 @@ def morse_decoder_thread(
     )
 
     try:
+        fd = rtl_stdout.fileno()
+
         while not stop_event.is_set():
-            data = rtl_stdout.read(CHUNK)
+            ready, _, _ = select.select([fd], [], [], 2.0)
+            if not ready:
+                # No data from SDR — emit diagnostic heartbeat
+                now = time.monotonic()
+                if now - last_scope >= SCOPE_INTERVAL:
+                    last_scope = now
+                    with contextlib.suppress(queue.Full):
+                        output_queue.put_nowait({
+                            'type': 'scope',
+                            'amplitudes': [],
+                            'threshold': 0,
+                            'tone_on': False,
+                            'waiting': True,
+                        })
+                continue
+
+            data = os.read(fd, CHUNK)
             if not data:
                 break