Rtty tx and rx (#2977)

firmware/application/external/rtty_tx/baudot.hpp

@@ -0,0 +1,28 @@
+#ifndef BAUDOT_HPP
+#define BAUDOT_HPP
+
+#include <cstdint>
+#include <string>
+
+namespace ui::external_app::rtty_tx {
+
+class BaudotCoder {
+   public:
+    enum ShiftState { LETTERS,
+                      FIGURES };
+
+    BaudotCoder()
+        : shiftState(LETTERS) {}
+    char decode(uint8_t baudotCode);
+    void encode(const std::string& src, uint8_t* dest, uint16_t* dest_length, uint16_t dest_max_size);
+    void set_usos(bool enable) { usos_enabled = enable; }  // shift == set to letters too
+
+   private:
+    ShiftState shiftState;
+    bool usos_enabled = true;
+    char get_char_mapping(bool is_figures, uint8_t index) const;
+};
+
+}  // namespace ui::external_app::rtty_tx
+
+#endif  // BAUDOT_HPP