Fixed RSSI indication confusion. Added SNR indication to received packets.

Config.h

@@ -4,7 +4,7 @@
 	#define CONFIG_H
 
 	#define MAJ_VERS  0x01
-	#define MIN_VERS  0x0A
+	#define MIN_VERS  0x0B
 
 	#define MCU_328P  0x90
 	#define MCU_1284P 0x91
@@ -62,10 +62,13 @@
 
 	// MCU independent configuration parameters
 	const long serial_baudrate  = 115200;
-	const int  rssi_offset      = 292;
-
 	const int lora_rx_turnaround_ms = 50;
 
+	// SX1276 RSSI offset to get dBm value from
+	// packet RSSI register
+	const int  rssi_offset      = 157;
+	const int  snr_offset       = 128;
+
 	// Default LoRa settings
 	int  lora_sf   	   = 0;
 	int  lora_cr       = 5;
@@ -85,6 +88,7 @@
 	
 	int		last_rssi		= -292;
 	uint8_t last_rssi_raw   = 0x00;
+	int8_t 	last_snr		= 0;
 	size_t	read_len		= 0;
 	uint8_t seq				= 0xFF;
 	uint8_t pbuf[MTU];

Framing.h

@@ -22,6 +22,7 @@
 	#define CMD_STAT_RX		0x21
 	#define CMD_STAT_TX		0x22
 	#define CMD_STAT_RSSI	0x23
+	#define CMD_STAT_SNR	0x24
 	#define CMD_BLINK		0x30
 	#define CMD_RANDOM		0x40
 

Libraries/Example.py

@@ -12,6 +12,8 @@ serialPort = "/dev/ttyUSB0"
 # packet is received
 def gotPacket(data, rnode):
 	print "Received a packet: "+data
+	print "RSSI: "+str(rnode.r_stat_rssi)+" dBm"
+	print "SNR:  "+str(rnode.r_stat_snr)+" dBm"
 
 # Create an RNode instance. This configures
 # and powers up the radio.

Libraries/RNode.py

@@ -27,6 +27,7 @@ class KISS():
 	CMD_STAT_RX		= chr(0x21)
 	CMD_STAT_TX		= chr(0x22)
 	CMD_STAT_RSSI	= chr(0x23)
+	CMD_STAT_SNR	= chr(0x24)
 	CMD_BLINK		= chr(0x30)
 	CMD_RANDOM		= chr(0x40)
 	CMD_FW_VERSION  = chr(0x50)
@@ -66,7 +67,8 @@ class RNodeInterface():
 	LOG_DEBUG    = 6
 	LOG_EXTREME  = 7
 
-	RSSI_OFFSET  = 292
+	RSSI_OFFSET  = 157
+	SNR_OFFSET  = 128
 
 	def __init__(self, callback, name, port, frequency = None, bandwidth = None, txpower = None, sf = None, cr = None, loglevel = -1, flow_control = True):
 		self.serial      = None
@@ -99,6 +101,7 @@ class RNodeInterface():
 		self.r_stat_rx   = None
 		self.r_stat_tx   = None
 		self.r_stat_rssi = None
+		self.r_stat_snr  = None
 		self.r_random	 = None
 
 		self.packet_queue    = []
@@ -310,6 +313,7 @@ class RNodeInterface():
 			while self.serial.is_open:
 				if self.serial.in_waiting:
 					byte = self.serial.read(1)
+					
 					last_read_ms = int(time.time()*1000)
 
 					if (in_frame and byte == KISS.FEND and command == KISS.CMD_DATA):
@@ -412,7 +416,29 @@ class RNodeInterface():
 									self.r_stat_tx = ord(command_buffer[0]) << 24 | ord(command_buffer[1]) << 16 | ord(command_buffer[2]) << 8 | ord(command_buffer[3])
 
 						elif (command == KISS.CMD_STAT_RSSI):
-							self.r_stat_rssi = ord(byte)-self.RSSI_OFFSET
+							if (byte == KISS.FESC):
+								escape = True
+							else:
+								if (escape):
+									if (byte == KISS.TFEND):
+										byte = KISS.FEND
+									if (byte == KISS.TFESC):
+										byte = KISS.FESC
+									escape = False
+								self.r_stat_rssi = ord(byte)-self.RSSI_OFFSET
+
+						elif (command == KISS.CMD_STAT_SNR):
+							if (byte == KISS.FESC):
+								escape = True
+							else:
+								if (escape):
+									if (byte == KISS.TFEND):
+										byte = KISS.FEND
+									if (byte == KISS.TFESC):
+										byte = KISS.FESC
+									escape = False
+								self.r_stat_snr  = ord(byte)-self.SNR_OFFSET
+
 						elif (command == KISS.CMD_RANDOM):
 							self.r_random = ord(byte)
 						elif (command == KISS.CMD_ERROR):

LoRa.cpp

@@ -218,10 +218,19 @@ uint8_t LoRaClass::packetRssiRaw() {
 }
 
 int LoRaClass::packetRssi() {
-  int pkt_rssi = (int)readRegister(REG_PKT_RSSI_VALUE);
+  int pkt_rssi = (int)readRegister(REG_PKT_RSSI_VALUE) - RSSI_OFFSET;
-  // TODO: change this to look at the actual model code
+  int pkt_snr = packetSnr();
+
   if (_frequency < 820E6) pkt_rssi -= 7;
-  pkt_rssi -= 157;
+
+  if (pkt_snr < 0) {
+    pkt_rssi += pkt_snr;
+  } else {
+    // Slope correction is (16/15)*pkt_rssi,
+    // this estimation looses one floating point
+    // operation, and should be precise enough.
+    pkt_rssi = (int)(1.066 * pkt_rssi);
+  }
 
   return pkt_rssi;
 }

LoRa.h

@@ -14,6 +14,8 @@
 #define PA_OUTPUT_RFO_PIN      0
 #define PA_OUTPUT_PA_BOOST_PIN 1
 
+#define RSSI_OFFSET 157
+
 class LoRaClass : public Stream {
 public:
   LoRaClass();

RNode_Firmware.ino

@@ -104,12 +104,14 @@ void receiveCallback(int packet_size) {
       read_len = 0;
       seq = sequence;
       last_rssi = LoRa.packetRssi();
+      last_snr = LoRa.packetSnr();
       getPacketData(packet_size);
     } else if (isSplitPacket(header) && seq == sequence) {
       // This is the second part of a split
       // packet, so we add it to the buffer
       // and set the ready flag.
       last_rssi = (last_rssi+LoRa.packetRssi())/2;
+      last_snr = (last_snr+LoRa.packetSnr())/2;
       getPacketData(packet_size);
       seq = SEQ_UNSET;
       ready = true;
@@ -121,6 +123,7 @@ void receiveCallback(int packet_size) {
       read_len = 0;
       seq = sequence;
       last_rssi = LoRa.packetRssi();
+      last_snr = LoRa.packetSnr();
       getPacketData(packet_size);
     } else if (!isSplitPacket(header)) {
       // This is not a split packet, so we
@@ -135,6 +138,7 @@ void receiveCallback(int packet_size) {
       }
 
       last_rssi = LoRa.packetRssi();
+      last_snr = LoRa.packetSnr();
       getPacketData(packet_size);
       ready = true;
     }
@@ -142,10 +146,8 @@ void receiveCallback(int packet_size) {
     if (ready) {
       // We first signal the RSSI of the
       // recieved packet to the host.
-      Serial.write(FEND);
+      kiss_indicate_stat_rssi();
-      Serial.write(CMD_STAT_RSSI);
+      kiss_indicate_stat_snr();
-      Serial.write((uint8_t)(last_rssi-rssi_offset));
-      Serial.write(FEND);
 
       // And then write the entire packet
       Serial.write(FEND);
@@ -168,10 +170,8 @@ void receiveCallback(int packet_size) {
 
     // We first signal the RSSI of the
     // recieved packet to the host.
-    Serial.write(FEND);
+    kiss_indicate_stat_rssi();
-    Serial.write(CMD_STAT_RSSI);
+    kiss_indicate_stat_snr();
-    Serial.write((uint8_t)(last_rssi-rssi_offset));
-    Serial.write(FEND);
 
     // And then write the entire packet
     Serial.write(FEND);

Utilities.h

@@ -133,7 +133,15 @@ void kiss_indicate_stat_rssi() {
 	uint8_t packet_rssi_val = (uint8_t)(last_rssi+rssi_offset);
 	Serial.write(FEND);
 	Serial.write(CMD_STAT_RSSI);
-	Serial.write(packet_rssi_val);
+	escapedSerialWrite(packet_rssi_val);
+	Serial.write(FEND);
+}
+
+void kiss_indicate_stat_snr() {
+	uint8_t packet_snr_val = (uint8_t)(last_snr+snr_offset);
+	Serial.write(FEND);
+	Serial.write(CMD_STAT_SNR);
+	escapedSerialWrite(packet_snr_val);
 	Serial.write(FEND);
 }