Improved channel access behaviour. Improved LoRa PHY parameter setup. Added parameter reporting to host connection.

Config.h

@@ -289,17 +289,24 @@
 
 	// MCU independent configuration parameters
 	const long serial_baudrate  = 115200;
-	const int lora_rx_turnaround_ms = 50;
-	uint8_t csma_p = 0;
-	float csma_p_min = 0.1;
-	float csma_p_max = 0.8;
-	int csma_slot_ms = lora_rx_turnaround_ms;
 
 	// SX1276 RSSI offset to get dBm value from
 	// packet RSSI register
 	const int  rssi_offset = 157;
 
 	// Default LoRa settings
+	const int lora_rx_turnaround_ms = 66;
+	const int lora_post_tx_yield_slots = 6;
+	uint32_t post_tx_yield_timeout = 0;
+	#define LORA_PREAMBLE_SYMBOLS_HW  4
+	#define LORA_PREAMBLE_SYMBOLS_MIN 6
+	#define LORA_PREAMBLE_TARGET_MS   15
+	#define LORA_CAD_SYMBOLS 3
+	int csma_slot_ms = 50;
+	float csma_p_min = 0.1;
+	float csma_p_max = 0.8;
+	uint8_t csma_p = 0;
+
 	int  lora_sf   	           = 0;
 	int  lora_cr               = 5;
 	int  lora_txp              = 0xFF;
@@ -378,10 +385,11 @@
 	bool dcd_waiting            = false;
 	long dcd_wait_until         = 0;
 	uint16_t dcd_count          = 0;
-	uint16_t dcd_threshold    = 6;
+	uint16_t dcd_threshold      = 2;
 
 	uint32_t status_interval_ms = STATUS_INTERVAL_MS;
 	uint32_t last_status_update = 0;
+	uint32_t last_dcd = 0;
 
 	// Status flags
 	const uint8_t SIG_DETECT = 0x01;

Framing.h

@@ -43,6 +43,7 @@
   #define CMD_STAT_RSSI   0x23
   #define CMD_STAT_SNR    0x24
   #define CMD_STAT_CHTM   0x25
+  #define CMD_STAT_PHYPRM 0x26
   #define CMD_BLINK       0x30
   #define CMD_RANDOM      0x40
 

RNode_Firmware.ino

@@ -318,7 +318,6 @@ bool startRadio() {
         setBandwidth();
         setSpreadingFactor();
         setCodingRate();
-        setPreamble();
         getFrequency();
 
         LoRa.enableCrc();
@@ -398,6 +397,7 @@ void flushQueue(void) {
 
     lora_receive();
     led_tx_off();
+    post_tx_yield_timeout = millis()+(lora_post_tx_yield_slots*csma_slot_ms);
   }
 
   queue_height = 0;
@@ -925,20 +925,30 @@ void updateModemStatus() {
   if (status & RX_ONGOING == RX_ONGOING) { stat_rx_ongoing = true; } else { stat_rx_ongoing = false; }
 
   if (stat_signal_detected || stat_signal_synced || stat_rx_ongoing) {
+    if (stat_rx_ongoing) {
       if (dcd_count < dcd_threshold) {
         dcd_count++;
-      dcd = true;
       } else {
-      dcd = true;
+        last_dcd = last_status_update;
         dcd_led = true;
+        dcd = true;
+      }
     }
   } else {
-    if (dcd_count > 0) {
+    #define DCD_LED_STEP_D 3
-      dcd_count = 0;
+    if (dcd_count == 0) {
-    } else {
       dcd_led = false;
+    } else if (dcd_count > DCD_LED_STEP_D) {
+      dcd_count -= DCD_LED_STEP_D;
+    } else {
+      dcd_count = 0;
     }
+
+    if (last_status_update > last_dcd+csma_slot_ms) {
       dcd = false;
+      dcd_led = false;
+      dcd_count = 0;
+    }
   }
 
   if (dcd_led) {
@@ -1110,8 +1120,6 @@ void validate_status() {
 
 void loop() {
   if (radio_online) {
-    checkModemStatus();
-
     #if MCU_VARIANT == MCU_ESP32
       if (packet_ready) {
         portENTER_CRITICAL(&update_lock);
@@ -1128,14 +1136,17 @@ void loop() {
       if (lt_airtime_limit != 0.0 && longterm_airtime >= lt_airtime_limit) airtime_lock = true;
     #endif
 
+    checkModemStatus();
     if (!airtime_lock) {
       if (queue_height > 0) {
         #if MCU_VARIANT == MCU_ESP32
-
-          if (dcd_waiting && (millis() >= dcd_wait_until)) { dcd_waiting = false; }
-          if (!dcd_waiting) {
-            updateModemStatus();
           long check_time = millis();
+          if (check_time > post_tx_yield_timeout) {
+            if (dcd_waiting && (check_time >= dcd_wait_until)) { dcd_waiting = false; }
+            if (!dcd_waiting) {
+              for (uint8_t dcd_i = 0; dcd_i < dcd_threshold*2; dcd_i++) {
+                delay(STATUS_INTERVAL_MS); updateModemStatus();
+              }
 
               if (!dcd) {
                 uint8_t csma_r = (uint8_t)random(256);
@@ -1143,7 +1154,8 @@ void loop() {
                   flushQueue();
                 } else {
                   dcd_waiting = true;
-                dcd_wait_until = check_time+csma_slot_ms;
+                  dcd_wait_until = millis()+csma_slot_ms;
+                }
               }
             }
           }

Utilities.h

@@ -732,6 +732,29 @@ void kiss_indicate_channel_stats() {
 	#endif
 }
 
+void kiss_indicate_phy_stats() {
+	#if MCU_VARIANT == MCU_ESP32
+		uint16_t lst = (uint16_t)(lora_symbol_time_ms*1000);
+		uint16_t lsr = (uint16_t)(lora_symbol_rate);
+		uint16_t prs = (uint16_t)(lora_preamble_symbols+4);
+		uint16_t prt = (uint16_t)((lora_preamble_symbols+4)*lora_symbol_time_ms);
+		uint16_t cst = (uint16_t)(csma_slot_ms);
+		serial_write(FEND);
+		serial_write(CMD_STAT_PHYPRM);
+		escaped_serial_write(lst>>8);
+		escaped_serial_write(lst);
+		escaped_serial_write(lsr>>8);
+		escaped_serial_write(lsr);
+		escaped_serial_write(prs>>8);
+		escaped_serial_write(prs);
+		escaped_serial_write(prt>>8);
+		escaped_serial_write(prt);
+		escaped_serial_write(cst>>8);
+		escaped_serial_write(cst);
+		serial_write(FEND);
+	#endif
+}
+
 void kiss_indicate_btpin() {
 	#if HAS_BLUETOOTH
 		serial_write(FEND);
@@ -905,6 +928,11 @@ inline uint8_t packetSequence(uint8_t header) {
 	return header >> 4;
 }
 
+void setPreamble() {
+	if (radio_online) LoRa.setPreambleLength(lora_preamble_symbols);
+	kiss_indicate_phy_stats();
+}
+
 void updateBitrate() {
 	#if MCU_VARIANT == MCU_ESP32
 		if (radio_online) {
@@ -912,7 +940,15 @@ void updateBitrate() {
 			lora_symbol_time_ms = (1.0/lora_symbol_rate)*1000.0;
 			lora_bitrate = (uint32_t)(lora_sf * ( (4.0/(float)lora_cr) / ((float)(pow(2, lora_sf))/((float)lora_bw/1000.0)) ) * 1000.0);
 			lora_us_per_byte = 1000000.0/((float)lora_bitrate/8.0);
-			csma_slot_ms = lora_symbol_time_ms*10;
+			// csma_slot_ms = lora_symbol_time_ms*10;
+			float target_preamble_symbols = (LORA_PREAMBLE_TARGET_MS/lora_symbol_time_ms)-LORA_PREAMBLE_SYMBOLS_HW;
+			if (target_preamble_symbols < LORA_PREAMBLE_SYMBOLS_MIN) {
+				target_preamble_symbols = LORA_PREAMBLE_SYMBOLS_MIN;
+			} else {
+				target_preamble_symbols = ceil(target_preamble_symbols);
+			}
+			lora_preamble_symbols = (long)target_preamble_symbols;
+			setPreamble();
 		} else {
 			lora_bitrate = 0;
 		}
@@ -929,11 +965,6 @@ void setCodingRate() {
 	updateBitrate();
 }
 
-void setPreamble() {
-	if (radio_online) LoRa.setPreambleLength(lora_preamble_symbols);
-	updateBitrate();
-}
-
 void set_implicit_length(uint8_t len) {
 	implicit_l = len;
 	if (implicit_l != 0) {