Fix coding rate on Short and Medium presets, add LongTurbo

docs/COMMON-ERRORS.md

@@ -360,6 +360,42 @@ something on air, could not classify it, moving on."
 
 **Fix:** None required. Safe to ignore.
 
+### My Short or Medium preset shows the wrong coding rate
+
+**Cause:** Meshpoints running v0.7.1 or earlier shipped the Short and
+Medium presets with `coding_rate: "4/8"` in the preset table. The
+correct value per the [Meshtastic spec](https://meshtastic.org/docs/overview/radio-settings/)
+is `4/5` for `ShortFast`, `ShortSlow`, `ShortTurbo`, `MediumFast`,
+`MediumSlow`, and `LongFast`. Only `LongModerate`, `LongSlow`,
+`LongTurbo`, and the deprecated `VeryLongSlow` use `4/8`.
+
+If you picked one of the affected presets in the dashboard Radio tab
+on a pre-fix install, your `config/local.yaml` has the wrong CR
+cached, even after `git pull`.
+
+**Impact:** RX is unaffected (the SX1302 decodes any CR automatically
+because the LoRa header carries it). TX takes roughly 60% more
+airtime than a stock Meshtastic node sending the "same" preset:
+4/8 has 2x overhead per data byte vs 4/5's 1.25x. NodeInfo broadcasts,
+DM ACKs, and relay (when enabled) all pay this airtime tax.
+
+**Fix:** After `sudo git pull origin main && sudo systemctl restart
+meshpoint`, do one of the following:
+
+- **Dashboard re-pick** (recommended): open the dashboard, go to the
+  Radio tab, re-select your preset from the Radio Configuration
+  dropdown, click Save Radio, and apply the restart prompt. This
+  rewrites `local.yaml` with the corrected CR.
+- **Manual edit**: edit `config/local.yaml` and set
+  `radio.coding_rate` to the correct value for your preset (`"4/5"`
+  for the six presets listed above, `"4/8"` for the four Long
+  presets). Then `sudo systemctl restart meshpoint`.
+
+To confirm the fix took effect, check the startup banner or
+`meshpoint status` for the active radio config, and watch the next
+NodeInfo broadcast log line: airtime should drop noticeably (e.g.,
+~723ms to ~456ms for a NodeInfo on MediumSlow).
+
 ---
 
 ## API and dashboard

src/config.py

@@ -43,7 +43,7 @@ class RadioConfig:
     slot: Optional[int] = None             # Meshtastic 1-indexed slot; used when frequency_mhz absent
     spreading_factor: int = 11
     bandwidth_khz: float = 250.0
-    coding_rate: str = "4/8"
+    coding_rate: str = "4/5"
     sync_word: int = 0x2B
     preamble_length: int = 16
     tx_power_dbm: int = 22

src/radio/presets.py

@@ -30,6 +30,13 @@ class ModemPreset:
         bandwidth_khz=250,
         coding_rate="4/5",
     ),
+    "LONG_TURBO": ModemPreset(
+        name="LONG_TURBO",
+        display_name="LongTurbo",
+        spreading_factor=11,
+        bandwidth_khz=500,
+        coding_rate="4/8",
+    ),
     "LONG_MODERATE": ModemPreset(
         name="LONG_MODERATE",
         display_name="LongModerate",
@@ -57,28 +64,28 @@ class ModemPreset:
         display_name="MediumFast",
         spreading_factor=9,
         bandwidth_khz=250,
-        coding_rate="4/8",
+        coding_rate="4/5",
     ),
     "MEDIUM_SLOW": ModemPreset(
         name="MEDIUM_SLOW",
         display_name="MediumSlow",
         spreading_factor=10,
         bandwidth_khz=250,
-        coding_rate="4/8",
+        coding_rate="4/5",
     ),
     "SHORT_FAST": ModemPreset(
         name="SHORT_FAST",
         display_name="ShortFast",
         spreading_factor=7,
         bandwidth_khz=250,
-        coding_rate="4/8",
+        coding_rate="4/5",
     ),
     "SHORT_SLOW": ModemPreset(
         name="SHORT_SLOW",
         display_name="ShortSlow",
         spreading_factor=8,
         bandwidth_khz=250,
-        coding_rate="4/8",
+        coding_rate="4/5",
     ),
     "SHORT_TURBO": ModemPreset(
         name="SHORT_TURBO",

src/transmit/tx_service.py

@@ -37,6 +37,7 @@
     (9, 250): "MediumFast",
     (10, 250): "MediumSlow",
     (11, 250): "LongFast",
+    (11, 500): "LongTurbo",
     (11, 125): "LongMod",
     (12, 125): "LongSlow",
     (12, 62): "VLongSlow",

tests/test_radio_presets_canonical.py

@@ -0,0 +1,85 @@
+"""Lock MODEM_PRESETS to the upstream Meshtastic spec.
+
+Each preset's (spreading_factor, bandwidth_khz, coding_rate) tuple
+must match the canonical Meshtastic firmware values to avoid silent
+drift like the v0.7.1-and-earlier bug where Short and Medium presets
+shipped with CR 4/8 instead of 4/5, costing ~60% extra airtime per TX.
+
+Reference: https://meshtastic.org/docs/overview/radio-settings/
+"""
+
+from __future__ import annotations
+
+import unittest
+
+from src.radio.presets import (
+    MODEM_PRESETS,
+    all_presets_list,
+    get_preset,
+    preset_from_params,
+)
+
+# Canonical (sf, bw_khz, cr) per upstream Meshtastic firmware
+# RadioInterface.cpp. Keys must match MODEM_PRESETS keys exactly.
+CANONICAL: dict[str, tuple[int, float, str]] = {
+    "SHORT_TURBO":    (7,  500,   "4/5"),
+    "SHORT_FAST":     (7,  250,   "4/5"),
+    "SHORT_SLOW":     (8,  250,   "4/5"),
+    "MEDIUM_FAST":    (9,  250,   "4/5"),
+    "MEDIUM_SLOW":    (10, 250,   "4/5"),
+    "LONG_FAST":      (11, 250,   "4/5"),
+    "LONG_TURBO":     (11, 500,   "4/8"),
+    "LONG_MODERATE":  (11, 125,   "4/8"),
+    "LONG_SLOW":      (12, 125,   "4/8"),
+    "VERY_LONG_SLOW": (12, 62.5,  "4/8"),
+}
+
+
+class TestPresetCanonicalValues(unittest.TestCase):
+
+    def test_full_preset_coverage(self):
+        """MODEM_PRESETS keys exactly match the canonical preset set."""
+        self.assertEqual(set(MODEM_PRESETS.keys()), set(CANONICAL.keys()))
+
+    def test_each_preset_matches_meshtastic_spec(self):
+        """Every preset's (sf, bw, cr) tuple matches upstream firmware."""
+        for name, expected in CANONICAL.items():
+            with self.subTest(preset=name):
+                p = MODEM_PRESETS[name]
+                actual = (p.spreading_factor, p.bandwidth_khz, p.coding_rate)
+                self.assertEqual(
+                    actual,
+                    expected,
+                    f"{name} drifted from upstream spec",
+                )
+
+    def test_get_preset_round_trip(self):
+        """get_preset() returns the same instance MODEM_PRESETS holds."""
+        for name in CANONICAL:
+            with self.subTest(preset=name):
+                self.assertIs(get_preset(name), MODEM_PRESETS[name])
+                self.assertIs(get_preset(name.lower()), MODEM_PRESETS[name])
+
+    def test_reverse_lookup_round_trips(self):
+        """preset_from_params(sf, bw, cr) returns the original preset name."""
+        for name, (sf, bw, cr) in CANONICAL.items():
+            with self.subTest(preset=name):
+                self.assertEqual(preset_from_params(sf, bw, cr), name)
+
+    def test_all_presets_list_includes_every_canonical_entry(self):
+        """API-facing all_presets_list() exposes every canonical preset."""
+        api_names = {entry["name"] for entry in all_presets_list()}
+        self.assertEqual(api_names, set(CANONICAL.keys()))
+
+    def test_long_turbo_is_tx_capable(self):
+        """LongTurbo mirrors ShortTurbo's tx_capable=True (BW500 region-aware)."""
+        self.assertTrue(MODEM_PRESETS["LONG_TURBO"].tx_capable)
+        self.assertTrue(MODEM_PRESETS["SHORT_TURBO"].tx_capable)
+
+    def test_very_long_slow_is_not_tx_capable(self):
+        """Deprecated VeryLongSlow remains RX-only per existing constraint."""
+        self.assertFalse(MODEM_PRESETS["VERY_LONG_SLOW"].tx_capable)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/test_tx_service.py

@@ -30,11 +30,14 @@ def test_shortturbo(self):
     def test_mediumfast(self):
         self.assertEqual(PRESET_DISPLAY_NAMES[(9, 250)], "MediumFast")
 
+    def test_longturbo(self):
+        self.assertEqual(PRESET_DISPLAY_NAMES[(11, 500)], "LongTurbo")
+
     def test_all_presets_present(self):
         expected = {
             "ShortFast", "ShortTurbo", "ShortSlow",
             "MediumFast", "MediumSlow",
-            "LongFast", "LongMod", "LongSlow", "VLongSlow",
+            "LongFast", "LongTurbo", "LongMod", "LongSlow", "VLongSlow",
         }
         self.assertEqual(set(PRESET_DISPLAY_NAMES.values()), expected)