[RTTY] Added support for Arduino flash strings

examples/RTTY/RTTY_Transmit/RTTY_Transmit.ino

@@ -93,6 +93,9 @@ void loop() {
   // character array (C-String)
   rtty.println("C-String");
 
+  // string saved in flash
+  rtty.println(F("Flash String"));
+
   // character
   rtty.println('c');
 

src/protocols/RTTY.cpp

@@ -187,6 +187,38 @@ size_t RTTYClient::write(uint8_t b) {
   return(1);
 }
 
+size_t RTTYClient::print(__FlashStringHelper* fstr) {
+  // read flash string length
+  size_t len = 0;
+  PGM_P p = reinterpret_cast<PGM_P>(fstr);
+  while(true) {
+    char c = pgm_read_byte(p++);
+    len++;
+    if(c == '\0') {
+      break;
+    }
+  }
+
+  // dynamically allocate memory
+  char* str = new char[len];
+
+  // copy string from flash
+  p = reinterpret_cast<PGM_P>(fstr);
+  for(size_t i = 0; i < len; i++) {
+    str[i] = pgm_read_byte(p + i);
+  }
+
+  size_t n = 0;
+  if(_encoding == ITA2) {
+    ITA2String ita2 = str;
+    n = RTTYClient::print(ita2);
+  } else if((_encoding == ASCII) || (_encoding == ASCII_EXTENDED)) {
+    n = RTTYClient::write((uint8_t*)str, len);
+  }
+  delete[] str;
+  return(n);
+}
+
 size_t RTTYClient::print(ITA2String& ita2) {
   uint8_t* arr = ita2.byteArr();
   size_t n = RTTYClient::write(arr, ita2.length());
@@ -277,6 +309,12 @@ size_t RTTYClient::println(void) {
   return(n);
 }
 
+size_t RTTYClient::println(__FlashStringHelper* fstr) {
+  size_t n = RTTYClient::print(fstr);
+  n += RTTYClient::println();
+  return(n);
+}
+
 size_t RTTYClient::println(ITA2String& ita2) {
   size_t n = RTTYClient::print(ita2);
   n += RTTYClient::println();

src/protocols/RTTY.h

@@ -112,6 +112,7 @@ class RTTYClient {
     size_t write(uint8_t* buff, size_t len);
     size_t write(uint8_t b);
 
+    size_t print(__FlashStringHelper*);
     size_t print(ITA2String &);
     size_t print(const String &);
     size_t print(const char[]);
@@ -124,6 +125,7 @@ class RTTYClient {
     size_t print(double, int = 2);
 
     size_t println(void);
+    size_t println(__FlashStringHelper*);
     size_t println(ITA2String &);
     size_t println(const String &s);
     size_t println(const char[]);