From 49d023379f8c3c35bab1e5c6c779f1d0f3a77fb4 Mon Sep 17 00:00:00 2001
From: Mark Qvist <mark@unsigned.io>
Date: Thu, 16 Jan 2025 23:01:46 +0100
Subject: [PATCH] Work around for SX1280 modem RSSI status latch on invalid
 preamble lengths

---
 sx128x.cpp | 51 +++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 43 insertions(+), 8 deletions(-)

diff --git a/sx128x.cpp b/sx128x.cpp
index a77920b..301dd0d 100644
--- a/sx128x.cpp
+++ b/sx128x.cpp
@@ -86,6 +86,11 @@ extern SPIClass SPI;
 
 #define MAX_PKT_LENGTH           255
 
+// #define PIN_PREAMBLE 38
+// #define PIN_HEADER   16
+// #define PIN_CAD      15
+// #define PIN_TRIG     39
+
 sx128x::sx128x() :
   _spiSettings(8E6, MSBFIRST, SPI_MODE0),
   _ss(LORA_DEFAULT_SS_PIN), _reset(LORA_DEFAULT_RESET_PIN), _dio0(LORA_DEFAULT_DIO0_PIN), _rxen(pin_rxen), _busy(LORA_DEFAULT_BUSY_PIN), _txen(pin_txen),
@@ -129,6 +134,12 @@ void sx128x::handleDio0Rise() {
 }
 
 bool sx128x::preInit() {
+  // pinMode(PIN_PREAMBLE, OUTPUT);
+  // pinMode(PIN_HEADER, OUTPUT);
+  // pinMode(PIN_CAD, OUTPUT);
+  // pinMode(PIN_TRIG, OUTPUT);
+  //////////////////////////
+
   pinMode(_ss, OUTPUT);
   digitalWrite(_ss, HIGH);
   
@@ -402,29 +413,53 @@ int sx128x::endPacket() {
 }
 
 unsigned long preamble_detected_at = 0;
-unsigned long header_detected_at = 0;
 extern long lora_preamble_time_ms;
 extern long lora_header_time_ms;
+bool false_preamble_detected = false;
 bool sx128x::dcd() {
+  bool preamble_detected = false;
+  bool header_detected = false;
   bool carrier_detected = false;
+  bool trig = false;
   uint8_t buf[2] = {0}; executeOpcodeRead(OP_GET_IRQ_STATUS_8X, buf, 2);
+  uint32_t header_detect_max_time = lora_preamble_time_ms + lora_header_time_ms;
+  uint32_t now = millis();
+
+  if ((buf[1] & IRQ_HEADER_DET_MASK_8X) != 0) {
+    preamble_detected = false;
+    header_detected = true;
+    carrier_detected = true;
+  } else { 
+    header_detected = false;
+  }
 
   if ((buf[0] & IRQ_PREAMBLE_DET_MASK_8X) != 0) {
     carrier_detected = true;
-    if (preamble_detected_at == 0) preamble_detected_at = millis();
-    if (millis() - preamble_detected_at > lora_preamble_time_ms + lora_header_time_ms) {
+    if (preamble_detected_at == 0) { preamble_detected_at = now; }
+    if (now - preamble_detected_at > header_detect_max_time) {
+      preamble_detected    = false;
       preamble_detected_at = 0;
-      uint8_t clearbuf[2] = {0};
+
+      if (!header_detected) { false_preamble_detected = true; }
+
+      uint8_t clearbuf[2]  = {0};
       clearbuf[0] = IRQ_PREAMBLE_DET_MASK_8X;
       executeOpcode(OP_CLEAR_IRQ_STATUS_8X, clearbuf, 2);
+      digitalWrite(PIN_PREAMBLE, LOW);
+
+    } else {
+      if (!header_detected) { preamble_detected = true; }
+      else                  { preamble_detected = false; }
     }
   }
 
-  if ((buf[1] & IRQ_HEADER_DET_MASK_8X) != 0) {
-    carrier_detected = true;
-    header_detected_at = millis();
-  }
+  // if (carrier_detected || preamble_detected || header_detected) { trig = true; }
+  // if (trig) { digitalWrite(PIN_TRIG, HIGH); } else { digitalWrite(PIN_TRIG, LOW); }
+  // if (preamble_detected) { digitalWrite(PIN_PREAMBLE, HIGH); } else { digitalWrite(PIN_PREAMBLE, LOW); }
+  // if (header_detected)   { digitalWrite(PIN_HEADER, HIGH); } else { digitalWrite(PIN_HEADER, LOW); }
+  // if (false_preamble_detected) { digitalWrite(PIN_CAD, HIGH); } else { digitalWrite(PIN_CAD, LOW); }
 
+  if (false_preamble_detected) { sx128x_modem.receive(); false_preamble_detected = false; }
   return carrier_detected;
 }