[AX.25] Added option to adjust audio frequencies (#346)

examples/AX25/AX25_Transmit_AFSK/AX25_Transmit_AFSK.ino

@@ -74,6 +74,22 @@ void setup() {
     Serial.println(state);
     while(true);
   }
+
+  // Sometimes, it may be required to adjust audio
+  // frequencies to match the expected 1200/2200 Hz tones.
+  // The following method will offset mark frequency by
+  // 100 Hz up and space frequency by 100 Hz down
+  /*
+    Serial.print(F("[AX.25] Setting correction ... "));
+    state = ax25.setCorrection(100, -100);
+    if(state == ERR_NONE) {
+      Serial.println(F("success!"));
+    } else {
+      Serial.print(F("failed, code "));
+      Serial.println(state);
+      while(true);
+    }
+  */
 }
 
 void loop() {

keywords.txt

@@ -230,6 +230,7 @@ setRepeaters	KEYWORD2
 setRecvSequence	KEYWORD2
 setSendSequence	KEYWORD2
 sendFrame	KEYWORD2
+setCorrection	KEYWORD2
 
 # SSTV
 sendHeader	KEYWORD2

src/protocols/AX25/AX25.cpp

@@ -160,6 +160,14 @@ AX25Client::AX25Client(PhysicalLayer* phy) {
 AX25Client::AX25Client(AFSKClient* audio) {
   _phy = audio->_phy;
   _audio = audio;
+  _afskMark = AX25_AFSK_MARK;
+  _afskSpace = AX25_AFSK_SPACE;
+}
+
+int16_t AX25Client::setCorrection(int16_t mark, int16_t space) {
+  _afskMark = AX25_AFSK_MARK + mark;
+  _afskSpace = AX25_AFSK_SPACE + space;
+  return(ERR_NONE);
 }
 #endif
 
@@ -393,9 +401,9 @@ int16_t AX25Client::sendFrame(AX25Frame* frame) {
       for(uint16_t mask = 0x80; mask >= 0x01; mask >>= 1) {
         uint32_t start = Module::micros();
         if(stuffedFrameBuff[i] & mask) {
-          _audio->tone(AX25_AFSK_MARK, false);
+          _audio->tone(_afskMark, false);
         } else {
-          _audio->tone(AX25_AFSK_SPACE, false);
+          _audio->tone(_afskSpace, false);
         }
         while(Module::micros() - start < AX25_AFSK_TONE_DURATION) {
           Module::yield();

src/protocols/AX25/AX25.h

@@ -292,6 +292,17 @@ class AX25Client {
       \param audio Pointer to the AFSK instance providing audio.
     */
     explicit AX25Client(AFSKClient* audio);
+
+    /*!
+      \brief Set AFSK tone correction offset. On some platforms, this is required to get the audio produced by the setup to match the expected 1200/2200 Hz tones.
+
+      \param mark Positive or negative correction offset for mark audio frequency in Hz.
+
+      \param space Positive or negative correction offset for space audio frequency in Hz.
+
+      \returns \ref status_codes
+    */
+    int16_t setCorrection(int16_t mark, int16_t space);
     #endif
 
     // basic methods
@@ -337,6 +348,8 @@ class AX25Client {
     PhysicalLayer* _phy;
     #if !defined(RADIOLIB_EXCLUDE_AFSK)
     AFSKClient* _audio;
+    uint32_t _afskMark;
+    uint32_t _afskSpace;
     #endif
 
     char _srcCallsign[AX25_MAX_CALLSIGN_LEN + 1] = {0, 0, 0, 0, 0, 0, 0};