From 58f6a3d6a3dc21a9e054e67053537dbfac35efc1 Mon Sep 17 00:00:00 2001
From: Mark Qvist <mark@unsigned.io>
Date: Wed, 8 Jan 2025 17:45:23 +0100
Subject: [PATCH] Reworked DCD methods for SX1276 and SX1280

---
 sx127x.cpp |  9 ++++++++-
 sx127x.h   |  7 ++++++-
 sx128x.cpp | 34 +++++++++++++++++++++-------------
 sx128x.h   |  2 +-
 4 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/sx127x.cpp b/sx127x.cpp
index 8871593..d354d9b 100644
--- a/sx127x.cpp
+++ b/sx127x.cpp
@@ -86,7 +86,6 @@ uint8_t ISR_VECT sx127x::readRegister(uint8_t address) { return singleTransfer(a
 void sx127x::writeRegister(uint8_t address, uint8_t value) { singleTransfer(address | 0x80, value); }
 void sx127x::standby() { writeRegister(REG_OP_MODE_7X, MODE_LONG_RANGE_MODE_7X | MODE_STDBY_7X); }
 void sx127x::sleep() { writeRegister(REG_OP_MODE_7X, MODE_LONG_RANGE_MODE_7X | MODE_SLEEP_7X); }
-uint8_t sx127x::modemStatus() { return readRegister(REG_MODEM_STAT_7X); }
 void sx127x::setSyncWord(uint8_t sw) { writeRegister(REG_SYNC_WORD_7X, sw); }
 void sx127x::enableCrc() { writeRegister(REG_MODEM_CONFIG_2_7X, readRegister(REG_MODEM_CONFIG_2_7X) | 0x04); }
 void sx127x::disableCrc() { writeRegister(REG_MODEM_CONFIG_2_7X, readRegister(REG_MODEM_CONFIG_2_7X) & 0xfb); }
@@ -195,6 +194,14 @@ int sx127x::endPacket() {
   return 1;
 }
 
+bool sx127x::dcd() {
+  bool carrier_detected = false;
+  uint8_t status = readRegister(REG_MODEM_STAT_7X);
+  if ((status & SIG_DETECT) == SIG_DETECT) { carrier_detected = true; }
+  if ((status & SIG_SYNCED) == SIG_SYNCED) { carrier_detected = true; }
+  return carrier_detected;
+}
+
 uint8_t sx127x::currentRssiRaw() {
     uint8_t rssi = readRegister(REG_RSSI_VALUE_7X);
     return rssi;
diff --git a/sx127x.h b/sx127x.h
index c87b636..7639857 100644
--- a/sx127x.h
+++ b/sx127x.h
@@ -18,6 +18,11 @@
 
 #define RSSI_OFFSET 157
 
+// Modem status flags
+#define SIG_DETECT 0x01
+#define SIG_SYNCED 0x02
+#define RX_ONGOING 0x04
+
 class sx127x : public Stream {
 public:
   sx127x();
@@ -65,7 +70,7 @@ public:
   void setCodingRate4(int denominator);
   void setPreambleLength(long preamble_symbols);
   void setSyncWord(uint8_t sw);
-  uint8_t modemStatus();
+  bool dcd();
   void enableCrc();
   void disableCrc();
   void enableTCXO();
diff --git a/sx128x.cpp b/sx128x.cpp
index 9aa6d7d..89fb70a 100644
--- a/sx128x.cpp
+++ b/sx128x.cpp
@@ -410,23 +410,31 @@ int sx128x::endPacket() {
   else           { return 1; }
 }
 
-uint8_t sx128x::modemStatus() {
-    // Imitate the register status from the sx1276 / 78
-    uint8_t buf[2] = {0};
-    executeOpcodeRead(OP_GET_IRQ_STATUS_8X, buf, 2);
-    uint8_t clearbuf[2] = {0};
-    uint8_t byte = 0x00;
+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 sx128x::dcd() {
+  bool carrier_detected = false;
+  uint8_t buf[2] = {0}; executeOpcodeRead(OP_GET_IRQ_STATUS_8X, buf, 2);
 
-    if ((buf[0] & IRQ_PREAMBLE_DET_MASK_8X) != 0) {
-        byte = byte | 0x01 | 0x04;
-        // Clear register after reading
-        clearbuf[0] = IRQ_PREAMBLE_DET_MASK_8X;
+  if ((buf[1] & 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) {
+      preamble_detected_at = 0;
+      uint8_t clearbuf[2] = {0};
+      clearbuf[1] = IRQ_PREAMBLE_DET_MASK_8X;
+      executeOpcode(OP_CLEAR_IRQ_STATUS_8X, clearbuf, 2);
     }
+  }
 
-    if ((buf[1] & IRQ_HEADER_DET_MASK_8X) != 0) { byte = byte | 0x02 | 0x04; }
-    executeOpcode(OP_CLEAR_IRQ_STATUS_8X, clearbuf, 2);
+  if ((buf[1] & IRQ_HEADER_DET_MASK_8X) != 0) {
+    carrier_detected = true;
+    header_detected_at = millis();
+  }
 
-    return byte;
+  return carrier_detected;
 }
 
 
diff --git a/sx128x.h b/sx128x.h
index 5977f7d..df15775 100644
--- a/sx128x.h
+++ b/sx128x.h
@@ -69,7 +69,7 @@ public:
   uint8_t getCodingRate4();
   void setPreambleLength(long preamble_symbols);
   void setSyncWord(int sw);
-  uint8_t modemStatus();
+  bool dcd();
   void clearIRQStatus();
   void enableCrc();
   void disableCrc();