fix mid band threshold and add function to get current RSSI value (#288)

* correct mid band threshold on rssi calculatio
* add function to get current rssi value from RegRssiValue

API.md

@@ -194,7 +194,7 @@ The `onReceive` callback will be called when a packet is received.
 int rssi = LoRa.packetRssi();
 ```
 
-Returns the RSSI of the received packet.
+Returns the averaged RSSI of the last received packet (dBm).
 
 ### Packet SNR
 
@@ -204,6 +204,14 @@ float snr = LoRa.packetSnr();
 
 Returns the estimated SNR of the received packet in dB.
 
+## RSSI
+
+```arduino
+int rssi = LoRa.rssi();
+```
+
+Returns the current RSSI of the radio (dBm). RSSI can be read at any time (during packet reception or not)
+
 ### Packet Frequency Error
 
 ```arduino

keywords.txt

@@ -23,6 +23,8 @@ packetRssi	KEYWORD2
 packetSnr	KEYWORD2
 packetFrequencyError	KEYWORD2
 
+rssi	KEYWORD2
+
 write	KEYWORD2
 
 available	KEYWORD2

src/LoRa.cpp

@@ -20,6 +20,7 @@
 #define REG_RX_NB_BYTES          0x13
 #define REG_PKT_SNR_VALUE        0x19
 #define REG_PKT_RSSI_VALUE       0x1a
+#define REG_RSSI_VALUE           0x1b
 #define REG_MODEM_CONFIG_1       0x1d
 #define REG_MODEM_CONFIG_2       0x1e
 #define REG_PREAMBLE_MSB         0x20
@@ -55,6 +56,10 @@
 #define IRQ_PAYLOAD_CRC_ERROR_MASK 0x20
 #define IRQ_RX_DONE_MASK           0x40
 
+#define RF_MID_BAND_THRESHOLD    525E6
+#define RSSI_OFFSET_HF_PORT      157
+#define RSSI_OFFSET_LF_PORT      164
+
 #define MAX_PKT_LENGTH           255
 
 #if (ESP8266 || ESP32)
@@ -258,7 +263,7 @@ int LoRaClass::parsePacket(int size)
 
 int LoRaClass::packetRssi()
 {
-  return (readRegister(REG_PKT_RSSI_VALUE) - (_frequency < 868E6 ? 164 : 157));
+  return (readRegister(REG_PKT_RSSI_VALUE) - (_frequency < RF_MID_BAND_THRESHOLD ? RSSI_OFFSET_LF_PORT : RSSI_OFFSET_HF_PORT));
 }
 
 float LoRaClass::packetSnr()
@@ -285,6 +290,11 @@ long LoRaClass::packetFrequencyError()
   return static_cast<long>(fError);
 }
 
+int LoRaClass::rssi()
+{
+  return (readRegister(REG_RSSI_VALUE) - (_frequency < RF_MID_BAND_THRESHOLD ? RSSI_OFFSET_LF_PORT : RSSI_OFFSET_HF_PORT));
+}
+
 size_t LoRaClass::write(uint8_t byte)
 {
   return write(&byte, sizeof(byte));

src/LoRa.h

@@ -45,6 +45,8 @@ public:
   float packetSnr();
   long packetFrequencyError();
 
+  int rssi();
+
   // from Print
   virtual size_t write(uint8_t byte);
   virtual size_t write(const uint8_t *buffer, size_t size);