Scale CAD scan timeouts to radio settings

src/helpers/radiolib/CadTiming.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <stdint.h>
+
+namespace mesh {
+
+static constexpr uint32_t CAD_SCAN_MIN_TIMEOUT_MS = 100UL;
+static constexpr uint32_t CAD_SCAN_MAX_TIMEOUT_MS = 3500UL;
+static constexpr uint32_t CAD_SCAN_FALLBACK_TIMEOUT_MS = 500UL;
+
+// RadioLib's SX126x CAD default examines four LoRa symbols. Allow six symbols
+// plus fixed command/TCXO overhead, then clamp the result so normal profiles
+// fail quickly without rejecting deliberately slow custom radio settings.
+inline uint32_t calculateCadScanTimeoutMillis(uint8_t sf, float bandwidth_khz) {
+  if (sf < 5 || sf > 12 || bandwidth_khz <= 0.0f) {
+    return CAD_SCAN_FALLBACK_TIMEOUT_MS;
+  }
+
+  const float symbol_ms = static_cast<float>(1UL << sf) / bandwidth_khz;
+  const float padded_ms = symbol_ms * 6.0f + 20.0f;
+  uint32_t timeout_ms = static_cast<uint32_t>(padded_ms + 0.999f);
+
+  if (timeout_ms < CAD_SCAN_MIN_TIMEOUT_MS) return CAD_SCAN_MIN_TIMEOUT_MS;
+  if (timeout_ms > CAD_SCAN_MAX_TIMEOUT_MS) return CAD_SCAN_MAX_TIMEOUT_MS;
+  return timeout_ms;
+}
+
+} // namespace mesh

src/helpers/radiolib/CustomSX1276Wrapper.h

@@ -42,7 +42,7 @@ public:
 
 protected:
   int16_t performChannelScan() override {
-    return ((CustomSX1276 *)_radio)->tryScanChannel(CAD_SCAN_TIMEOUT_MS, *_board);
+    return ((CustomSX1276 *)_radio)->tryScanChannel(cadScanTimeoutMillis(), *_board);
   }
 
   bool radioDeepInit() override {

src/helpers/radiolib/RadioLibWrappers.cpp

@@ -625,9 +625,10 @@ int16_t RadioLibWrapper::performChannelScan() {
   int16_t result = _radio->startChannelScan();
   if (result != RADIOLIB_ERR_NONE) return result;
 
+  const unsigned long timeout_ms = cadScanTimeoutMillis();
   const unsigned long started = millis();
   unsigned long last_watchdog_service = started;
-  while (millis() - started < CAD_SCAN_TIMEOUT_MS) {
+  while (millis() - started < timeout_ms) {
     result = _radio->getChannelScanResult();
     if (result != RADIOLIB_ERR_UNKNOWN) return result;
 
@@ -639,7 +640,7 @@ int16_t RadioLibWrapper::performChannelScan() {
     yield();
   }
 
-  MESH_DEBUG_PRINTLN("RadioLibWrapper: CAD scan timed out");
+  MESH_DEBUG_PRINTLN("RadioLibWrapper: CAD scan timed out after %lu ms", timeout_ms);
   return RADIOLIB_ERR_RX_TIMEOUT;
 }
 

src/helpers/radiolib/RadioLibWrappers.h

@@ -2,6 +2,7 @@
 
 #include <Mesh.h>
 #include <RadioLib.h>
+#include "CadTiming.h"
 
 // Fallback RX powersaving timings, only used until setRxPowerSaving() is called
 // (begin() always applies the persisted values). The authoritative defaults live
@@ -12,7 +13,6 @@
 
 class RadioLibWrapper : public mesh::Radio {
 protected:
-  static constexpr unsigned long CAD_SCAN_TIMEOUT_MS = 10000UL;
   PhysicalLayer* _radio;
   mesh::MainBoard* _board;
   uint32_t n_recv, n_sent, n_recv_errors;
@@ -72,6 +72,11 @@ protected:
   void cacheParams(float freq, float bw, uint8_t sf, uint8_t cr) {
     _cur_freq = freq; _cur_bw = bw; _cur_sf = sf; _cur_cr = cr; _params_valid = true;
   }
+  unsigned long cadScanTimeoutMillis() const {
+    const uint8_t sf = _params_valid ? _cur_sf : getSpreadingFactor();
+    const float bw = _params_valid ? _cur_bw : static_cast<float>(LORA_BW);
+    return mesh::calculateCadScanTimeoutMillis(sf, bw);
+  }
   virtual int startReceiveMode();
   virtual void stopReceiveDutyCycle();
   virtual bool isPacketReady();

test/test_cad_timing/test_cad_timing.cpp

@@ -0,0 +1,23 @@
+#include <gtest/gtest.h>
+
+#include <helpers/radiolib/CadTiming.h>
+
+TEST(CadTiming, UsesShortDeadlineForCascadeProfile) {
+  EXPECT_EQ(mesh::calculateCadScanTimeoutMillis(7, 62.5f), 100UL);
+}
+
+TEST(CadTiming, ScalesForSlowRadioSettings) {
+  EXPECT_EQ(mesh::calculateCadScanTimeoutMillis(12, 62.5f), 414UL);
+  EXPECT_EQ(mesh::calculateCadScanTimeoutMillis(12, 7.8f), 3171UL);
+}
+
+TEST(CadTiming, BoundsInvalidAndExtremeInputs) {
+  EXPECT_EQ(mesh::calculateCadScanTimeoutMillis(0, 62.5f), 500UL);
+  EXPECT_EQ(mesh::calculateCadScanTimeoutMillis(7, 0.0f), 500UL);
+  EXPECT_EQ(mesh::calculateCadScanTimeoutMillis(12, 1.0f), 3500UL);
+}
+
+int main(int argc, char** argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}