Issue 85 setting ldo flag (#121)

* Add getting the frequency error of a packet

* Update for review comments

* Add functions to set low data rate optimization flag

* Typo

* Fixes

* Add packetFrequencyError to API.md

* WIP

* Simplify

* Make getSpreadingFactor private

* Correct LDO bit calculation

* Update LDO determination

* Correct calculation

* Correct calculation

* Revert back to old LDO calculation

Author: torntrousers

src/LoRa.cpp

@@ -373,6 +373,11 @@ void LoRaClass::setFrequency(long frequency)
   writeRegister(REG_FRF_LSB, (uint8_t)(frf >> 0));
 }
 
+int LoRaClass::getSpreadingFactor()
+{
+  return readRegister(REG_MODEM_CONFIG_2) >> 4;
+}
+
 void LoRaClass::setSpreadingFactor(int sf)
 {
   if (sf < 6) {
@@ -390,22 +395,23 @@ void LoRaClass::setSpreadingFactor(int sf)
   }
 
   writeRegister(REG_MODEM_CONFIG_2, (readRegister(REG_MODEM_CONFIG_2) & 0x0f) | ((sf << 4) & 0xf0));
+  setLdoFlag();
 }
 
 long LoRaClass::getSignalBandwidth()
 {
   byte bw = (readRegister(REG_MODEM_CONFIG_1) >> 4);
   switch (bw) {
     case 0: return 7.8E3;
-    case 1: return 10.4E3; 
-    case 2: return 15.6E3; 
-    case 3: return 20.8E3; 
-    case 4: return 31.25E3; 
-    case 5: return 41.7E3; 
-    case 6: return 62.5E3; 
-    case 7: return 125E3; 
-    case 8: return 250E3; 
-    case 9: return 500E3; 
+    case 1: return 10.4E3;
+    case 2: return 15.6E3;
+    case 3: return 20.8E3;
+    case 4: return 31.25E3;
+    case 5: return 41.7E3;
+    case 6: return 62.5E3;
+    case 7: return 125E3;
+    case 8: return 250E3;
+    case 9: return 500E3;
   }
 }
 
@@ -436,6 +442,20 @@ void LoRaClass::setSignalBandwidth(long sbw)
   }
 
   writeRegister(REG_MODEM_CONFIG_1, (readRegister(REG_MODEM_CONFIG_1) & 0x0f) | (bw << 4));
+  setLdoFlag();
+}
+
+void LoRaClass::setLdoFlag()
+{
+  // Section 4.1.1.5
+  long symbolDuration = 1000 / ( getSignalBandwidth() / (1L << getSpreadingFactor()) ) ;
+    
+  // Section 4.1.1.6
+  boolean ldoOn = symbolDuration > 16;
+    
+  uint8_t config3 = readRegister(REG_MODEM_CONFIG_3);
+  bitWrite(config3, 3, ldoOn);
+  writeRegister(REG_MODEM_CONFIG_3, config3);
 }
 
 void LoRaClass::setCodingRate4(int denominator)

src/LoRa.h

@@ -72,8 +72,11 @@ class LoRaClass : public Stream {
 
   void handleDio0Rise();
 
+  int getSpreadingFactor();
   long getSignalBandwidth();
 
+  void setLdoFlag();
+
   uint8_t readRegister(uint8_t address);
   void writeRegister(uint8_t address, uint8_t value);
   uint8_t singleTransfer(uint8_t address, uint8_t value);