Add function to invert IQ signal register (#179)

Add function to change register (REG_INVERTIQ) to support communication node and gateway

The register does not exist in datasheet but use on but used in Semtech code.
Reference : https://github.com/intel-iot-devkit/upm/blob/master/src/sx1276/sx1276.cxx

* Add LoRa Simple Gateway/Node Exemple

Example how to use InvertIQ function to create a simple Gateway/Node logic.

API.md

@@ -329,6 +329,16 @@ LoRa.enableCrc();
 LoRa.disableCrc();
 ```
 
+### Invert IQ Signals
+
+Enable or disable Invert the LoRa I and Q signals, by default a invertIQ is not used.
+
+```arduino
+LoRa.enableInvertIQ();
+
+LoRa.disableInvertIQ();
+```
+
 ## Other functions
 
 ### Random

examples/LoRaSimpleGateway/LoRaSimpleGateway.ino

@@ -0,0 +1,113 @@
+/*
+  LoRa Simple Gateway/Node Exemple
+
+  This code uses InvertIQ function to create a simple Gateway/Node logic.
+
+  Gateway - Sends messages with enableInvertIQ()
+          - Receives messages with disableInvertIQ()
+
+  Node    - Sends messages with disableInvertIQ()
+          - Receives messages with enableInvertIQ()
+
+  With this arrangement a Gateway never receive messages from another Gateway
+  and a Node never receive message from another Node.
+  Only Gateway to Node and vice versa.
+
+  This code receives messages and sends a message every second.
+
+  InvertIQ function basically invert the LoRa I and Q signals.
+
+  See the Semtech datasheet, http://www.semtech.com/images/datasheet/sx1276.pdf
+  for more on InvertIQ register 0x33.
+
+  created 05 August 2018
+  by Luiz H. Cassettari
+*/
+
+#include <SPI.h>              // include libraries
+#include <LoRa.h>
+
+const long frequency = 915E6;  // LoRa Frequency
+
+const int csPin = 10;          // LoRa radio chip select
+const int resetPin = 9;        // LoRa radio reset
+const int irqPin = 2;          // change for your board; must be a hardware interrupt pin
+
+void setup() {
+  Serial.begin(9600);                   // initialize serial
+  while (!Serial);
+
+  LoRa.setPins(csPin, resetPin, irqPin);
+
+  if (!LoRa.begin(frequency)) {
+    Serial.println("LoRa init failed. Check your connections.");
+    while (true);                       // if failed, do nothing
+  }
+
+  Serial.println("LoRa init succeeded.");
+  Serial.println();
+  Serial.println("LoRa Simple Gateway");
+  Serial.println("Only receive messages from nodes");
+  Serial.println("Tx: invertIQ enable");
+  Serial.println("Rx: invertIQ disable");
+  Serial.println();
+
+  LoRa.onReceive(onReceive);
+  LoRa_rxMode();
+}
+
+void loop() {
+  if (runEvery(5000)) { // repeat every 5000 millis
+
+    String message = "HeLoRa World! ";
+    message += "I'm a Gateway! ";
+    message += millis();
+
+    LoRa_sendMessage(message); // send a message
+
+    Serial.println("Send Message!");
+  }
+}
+
+void LoRa_rxMode(){
+  LoRa.disableInvertIQ();               // normal mode
+  LoRa.receive();                       // set receive mode
+}
+
+void LoRa_txMode(){
+  LoRa.idle();                          // set standby mode
+  LoRa.enableInvertIQ();                // active invert I and Q signals
+}
+
+void LoRa_sendMessage(String message) {
+  LoRa_txMode();                        // set tx mode
+  LoRa.beginPacket();                   // start packet
+  LoRa.print(message);                  // add payload
+  LoRa.endPacket();                     // finish packet and send it
+  LoRa_rxMode();                        // set rx mode
+}
+
+void onReceive(int packetSize) {
+  String message = "";
+
+  while (LoRa.available()) {
+    message += (char)LoRa.read();
+  }
+
+  Serial.print("Gateway Receive: ");
+  Serial.println(message);
+
+}
+
+boolean runEvery(unsigned long interval)
+{
+  static unsigned long previousMillis = 0;
+  unsigned long currentMillis = millis();
+  if (currentMillis - previousMillis >= interval)
+  {
+    previousMillis = currentMillis;
+    return true;
+  }
+  return false;
+}
+

examples/LoRaSimpleNode/LoRaSimpleNode.ino

@@ -0,0 +1,113 @@
+/*
+  LoRa Simple Gateway/Node Exemple
+
+  This code uses InvertIQ function to create a simple Gateway/Node logic.
+
+  Gateway - Sends messages with enableInvertIQ()
+          - Receives messages with disableInvertIQ()
+
+  Node    - Sends messages with disableInvertIQ()
+          - Receives messages with enableInvertIQ()
+
+  With this arrangement a Gateway never receive messages from another Gateway
+  and a Node never receive message from another Node.
+  Only Gateway to Node and vice versa.
+
+  This code receives messages and sends a message every second.
+
+  InvertIQ function basically invert the LoRa I and Q signals.
+
+  See the Semtech datasheet, http://www.semtech.com/images/datasheet/sx1276.pdf
+  for more on InvertIQ register 0x33.
+
+  created 05 August 2018
+  by Luiz H. Cassettari
+*/
+
+#include <SPI.h>              // include libraries
+#include <LoRa.h>
+
+const long frequency = 915E6;  // LoRa Frequency
+
+const int csPin = 10;          // LoRa radio chip select
+const int resetPin = 9;        // LoRa radio reset
+const int irqPin = 2;          // change for your board; must be a hardware interrupt pin
+
+void setup() {
+  Serial.begin(9600);                   // initialize serial
+  while (!Serial);
+
+  LoRa.setPins(csPin, resetPin, irqPin);
+
+  if (!LoRa.begin(frequency)) {
+    Serial.println("LoRa init failed. Check your connections.");
+    while (true);                       // if failed, do nothing
+  }
+
+  Serial.println("LoRa init succeeded.");
+  Serial.println();
+  Serial.println("LoRa Simple Node");
+  Serial.println("Only receive messages from gateways");
+  Serial.println("Tx: invertIQ disable");
+  Serial.println("Rx: invertIQ enable");
+  Serial.println();
+
+  LoRa.onReceive(onReceive);
+  LoRa_rxMode();
+}
+
+void loop() {
+  if (runEvery(1000)) { // repeat every 1000 millis
+
+    String message = "HeLoRa World! ";
+    message += "I'm a Node! ";
+    message += millis();
+
+    LoRa_sendMessage(message); // send a message
+
+    Serial.println("Send Message!");
+  }
+}
+
+void LoRa_rxMode(){
+  LoRa.enableInvertIQ();                // active invert I and Q signals
+  LoRa.receive();                       // set receive mode
+}
+
+void LoRa_txMode(){
+  LoRa.idle();                          // set standby mode
+  LoRa.disableInvertIQ();               // normal mode
+}
+
+void LoRa_sendMessage(String message) {
+  LoRa_txMode();                        // set tx mode
+  LoRa.beginPacket();                   // start packet
+  LoRa.print(message);                  // add payload
+  LoRa.endPacket();                     // finish packet and send it
+  LoRa_rxMode();                        // set rx mode
+}
+
+void onReceive(int packetSize) {
+  String message = "";
+
+  while (LoRa.available()) {
+    message += (char)LoRa.read();
+  }
+
+  Serial.print("Node Receive: ");
+  Serial.println(message);
+
+}
+
+boolean runEvery(unsigned long interval)
+{
+  static unsigned long previousMillis = 0;
+  unsigned long currentMillis = millis();
+  if (currentMillis - previousMillis >= interval)
+  {
+    previousMillis = currentMillis;
+    return true;
+  }
+  return false;
+}
+

keywords.txt

@@ -44,6 +44,8 @@ setPreambleLength	KEYWORD2
 setSyncWord	KEYWORD2
 enableCrc	KEYWORD2
 disableCrc	KEYWORD2
+enableInvertIQ  KEYWORD2
+disableInvertIQ KEYWORD2
 
 random	KEYWORD2
 setPins	KEYWORD2

src/LoRa.cpp

@@ -31,8 +31,10 @@
 #define REG_FREQ_ERROR_LSB       0x2a
 #define REG_RSSI_WIDEBAND        0x2c
 #define REG_DETECTION_OPTIMIZE   0x31
+#define REG_INVERTIQ             0x33
 #define REG_DETECTION_THRESHOLD  0x37
 #define REG_SYNC_WORD            0x39
+#define REG_INVERTIQ2            0x3b
 #define REG_DIO_MAPPING_1        0x40
 #define REG_VERSION              0x42
 #define REG_PA_DAC               0x4d
@@ -531,6 +533,18 @@ void LoRaClass::disableCrc()
   writeRegister(REG_MODEM_CONFIG_2, readRegister(REG_MODEM_CONFIG_2) & 0xfb);
 }
 
+void LoRaClass::enableInvertIQ()
+{
+  writeRegister(REG_INVERTIQ,  0x66);
+  writeRegister(REG_INVERTIQ2, 0x19);
+}
+
+void LoRaClass::disableInvertIQ()
+{
+  writeRegister(REG_INVERTIQ,  0x27);
+  writeRegister(REG_INVERTIQ2, 0x1d);
+}
+
 void LoRaClass::setOCP(uint8_t mA)
 {
   uint8_t ocpTrim = 27;

src/LoRa.h

@@ -66,6 +66,9 @@ public:
   void setSyncWord(int sw);
   void enableCrc();
   void disableCrc();
+  void enableInvertIQ();
+  void disableInvertIQ();
+  
   void setOCP(uint8_t mA); // Over Current Protection control
 
   // deprecated