From 89bd6c3416252365cf596f9e9e0fba590a1e934c Mon Sep 17 00:00:00 2001
From: Scott Powell <sqij@protonmail.com>
Date: Fri, 28 Mar 2025 20:50:42 +1100
Subject: [PATCH] * Dispatcher: now impose a max time for CAD fail (ie. channel
 busy), defined by getCADFailMaxDuration(), default 4 seconds. (an sx126x bug
 _might_ be making radio->isReceiving() return true indefinitely)

---
 src/Dispatcher.cpp | 18 ++++++++++++++++--
 src/Dispatcher.h   |  3 +++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/src/Dispatcher.cpp b/src/Dispatcher.cpp
index 65f9687f..ae225d36 100644
--- a/src/Dispatcher.cpp
+++ b/src/Dispatcher.cpp
@@ -29,6 +29,9 @@ int Dispatcher::calcRxDelay(float score, uint32_t air_time) const {
 uint32_t Dispatcher::getCADFailRetryDelay() const {
   return 200;
 }
+uint32_t Dispatcher::getCADFailMaxDuration() const {
+  return 4000;   // 4 seconds
+}
 
 void Dispatcher::loop() {
   if (outbound) {  // waiting for outbound send to be completed
@@ -185,9 +188,20 @@ void Dispatcher::checkSend() {
   if (_mgr->getOutboundCount() == 0) return;  // nothing waiting to send
   if (!millisHasNowPassed(next_tx_time)) return;   // still in 'radio silence' phase (from airtime budget setting)
   if (_radio->isReceiving()) {   // LBT - check if radio is currently mid-receive, or if channel activity
-    next_tx_time = futureMillis(getCADFailRetryDelay());
-    return; 
+    if (cad_busy_start == 0) {
+      cad_busy_start = _ms->getMillis();   // record when CAD busy state started
+    }
+
+    if (_ms->getMillis() - cad_busy_start > getCADFailMaxDuration()) {
+      MESH_DEBUG_PRINTLN("%s Dispatcher::checkSend(): CAD busy max duration reached!", getLogDateTime());
+      // channel activity has gone on too long... (Radio might be in a bad state)
+      // force the pending transmit below...
+    } else {
+      next_tx_time = futureMillis(getCADFailRetryDelay());
+      return;
+    }
   }
+  cad_busy_start = 0;  // reset busy state
 
   outbound = _mgr->getNextOutbound(_ms->getMillis());
   if (outbound) {
diff --git a/src/Dispatcher.h b/src/Dispatcher.h
index 0b00f1a9..393d0856 100644
--- a/src/Dispatcher.h
+++ b/src/Dispatcher.h
@@ -98,6 +98,7 @@ class Dispatcher {
   Packet* outbound;  // current outbound packet
   unsigned long outbound_expiry, outbound_start, total_air_time;
   unsigned long next_tx_time;
+  unsigned long cad_busy_start;
   uint32_t n_sent_flood, n_sent_direct;
   uint32_t n_recv_flood, n_recv_direct;
   uint32_t n_full_events;
@@ -113,6 +114,7 @@ protected:
     : _radio(&radio), _ms(&ms), _mgr(&mgr)
   {
     outbound = NULL; total_air_time = 0; next_tx_time = 0;
+    cad_busy_start = 0;
   }
 
   virtual DispatcherAction onRecvPacket(Packet* pkt) = 0;
@@ -127,6 +129,7 @@ protected:
   virtual float getAirtimeBudgetFactor() const;
   virtual int calcRxDelay(float score, uint32_t air_time) const;
   virtual uint32_t getCADFailRetryDelay() const;
+  virtual uint32_t getCADFailMaxDuration() const;
 
 public:
   void begin();