prepare_data

prepare_frame.cpp

// -------------------- Payload preparation --------------------
// Format: little-endian float32 (°C), to match the decodeUplink() shown.
static void prepareTxFrame(void) {
  float t = temperatureRead();                 // ESP32 on-die sensor (not ambient)
  last_temp_cX100 = (int16_t) lroundf(t * 100.0f); // keep your existing status display state

  // Serialize float32 to little-endian bytes explicitly
  static_assert(sizeof(float) == 4, "float must be 4 bytes (IEEE-754)");
  uint32_t raw;
  memcpy(&raw, &t, sizeof(raw));

  appDataSize = 4;
  appData[0] = (uint8_t)((raw >> 0)  & 0xFF);  // LSB
  appData[1] = (uint8_t)((raw >> 8)  & 0xFF);
  appData[2] = (uint8_t)((raw >> 16) & 0xFF);
  appData[3] = (uint8_t)((raw >> 24) & 0xFF);  // MSB

  Serial.print("Temp (C): ");
  Serial.println(t);

  // Reuse your display helper; it expects centi-degrees
  display_temperature_centi(last_temp_cX100);
}