From f31781cf751d2fb075b36f39aa319e8d0a73adf7 Mon Sep 17 00:00:00 2001
From: FUJIURA Toyonori <toyokun@gmail.com>
Date: Mon, 28 Mar 2022 10:15:37 +0900
Subject: [PATCH] Collision avoidance.

---
 lib/LoRa/LoRa.cpp |  5 +++++
 lib/LoRa/LoRa.h   |  1 +
 src/TaskModem.cpp | 17 +++++++++++------
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/lib/LoRa/LoRa.cpp b/lib/LoRa/LoRa.cpp
index 35dfacd..2422ca8 100644
--- a/lib/LoRa/LoRa.cpp
+++ b/lib/LoRa/LoRa.cpp
@@ -18,6 +18,7 @@
 #define REG_FIFO_RX_CURRENT_ADDR 0x10
 #define REG_IRQ_FLAGS            0x12
 #define REG_RX_NB_BYTES          0x13
+#define REG_MODEM_STAT           0x18
 #define REG_PKT_SNR_VALUE        0x19
 #define REG_PKT_RSSI_VALUE       0x1a
 #define REG_RSSI_VALUE           0x1b
@@ -251,6 +252,10 @@ float LoRaClass::packetSnr() {
   return ((int8_t)readRegister(REG_PKT_SNR_VALUE)) * 0.25;
 }
 
+bool LoRaClass::rxSignalDetected() {
+  return (readRegister(REG_MODEM_STAT) & 0x01) == 0x01;
+}
+
 long LoRaClass::packetFrequencyError() {
   int32_t freqError = 0;
   freqError         = static_cast<int32_t>(readRegister(REG_FREQ_ERROR_MSB) & B111);
diff --git a/lib/LoRa/LoRa.h b/lib/LoRa/LoRa.h
index 51e089a..45c92bd 100644
--- a/lib/LoRa/LoRa.h
+++ b/lib/LoRa/LoRa.h
@@ -44,6 +44,7 @@ public:
   int packetRssi();
   float packetSnr();
   long packetFrequencyError();
+  bool rxSignalDetected();
 
   int rssi();
 
diff --git a/src/TaskModem.cpp b/src/TaskModem.cpp
index ca0784d..017b2b2 100644
--- a/src/TaskModem.cpp
+++ b/src/TaskModem.cpp
@@ -45,13 +45,18 @@ bool ModemTask::loop(System &system) {
   }
 
   if (!_toModem.empty()) {
-    std::shared_ptr<APRSMessage> msg = _toModem.getElement();
-    if (system.getUserConfig()->lora.tx_enable) {
-      system.getLogger().log(logging::LoggerLevel::LOGGER_LEVEL_DEBUG, getName(), "[%s] Transmitting packet '%s'", timeString().c_str(), msg->toString().c_str());
-      _lora_aprs.sendMessage(msg);
-      system.getLogger().log(logging::LoggerLevel::LOGGER_LEVEL_DEBUG, getName(), "[%s] TX done", timeString().c_str());
+    if (_lora_aprs.rxSignalDetected()) {
+      system.getLogger().log(logging::LoggerLevel::LOGGER_LEVEL_DEBUG, getName(), "[%s] RX signal detected. Waiting TX", timeString().c_str());
+      delay(1000);
     } else {
-      system.getLogger().log(logging::LoggerLevel::LOGGER_LEVEL_DEBUG, getName(), "[%s] NOT transmitting packet as TX is not enabled '%s'", timeString().c_str(), msg->toString().c_str());
+      std::shared_ptr<APRSMessage> msg = _toModem.getElement();
+      if (system.getUserConfig()->lora.tx_enable) {
+        system.getLogger().log(logging::LoggerLevel::LOGGER_LEVEL_DEBUG, getName(), "[%s] Transmitting packet '%s'", timeString().c_str(), msg->toString().c_str());
+        _lora_aprs.sendMessage(msg);
+        system.getLogger().log(logging::LoggerLevel::LOGGER_LEVEL_DEBUG, getName(), "[%s] TX done", timeString().c_str());
+      } else {
+        system.getLogger().log(logging::LoggerLevel::LOGGER_LEVEL_DEBUG, getName(), "[%s] NOT transmitting packet as TX is not enabled '%s'", timeString().c_str(), msg->toString().c_str());
+      }
     }
   }