|-- <BluetoothSerial> 1.0
Building in release mode
Compiling .pio\build\esp32doit-devkit-v1\src\main.cpp.o
Linking .pio\build\esp32doit-devkit-v1\firmware.elf
.pio\build\esp32doit-devkit-v1\src\bluetooth.cpp.o:(.literal._Z7bt_initv+0x20): undefined reference to `BluetoothSerial::begin(String, bool)'
.pio\build\esp32doit-devkit-v1\src\bluetooth.cpp.o:(.literal.startup._GLOBAL__sub_I_SerialBth+0x4): undefined reference to `BluetoothSerial::BluetoothSerial()'
.pio\build\esp32doit-devkit-v1\src\bluetooth.cpp.o:(.literal._Z7readBthv+0x14): undefined reference to `BluetoothSerial::read()'
.pio\build\esp32doit-devkit-v1\src\bluetooth.cpp.o:(.literal.exit._GLOBAL__sub_D_SerialBth+0x0): undefined reference to `BluetoothSerial::~BluetoothSerial()'
.pio\build\esp32doit-devkit-v1\src\bluetooth.cpp.o: In function `bt_init()':
C:\Users\Cemal\Documents\PlatformIO\Projects\r2k_bth/src/bluetooth.cpp:18: undefined reference to `BluetoothSerial::begin(String, bool)'
.pio\build\esp32doit-devkit-v1\src\bluetooth.cpp.o: In function `_GLOBAL__sub_I_SerialBth':
C:\Users\Cemal\Documents\PlatformIO\Projects\r2k_bth/src/bluetooth.cpp:18: undefined reference to `BluetoothSerial::BluetoothSerial()'
.pio\build\esp32doit-devkit-v1\src\bluetooth.cpp.o: In function `readBth()':
C:\Users\Cemal\Documents\PlatformIO\Projects\r2k_bth/src/bluetooth.cpp:25: undefined reference to `BluetoothSerial::read()'
C:\Users\Cemal\Documents\PlatformIO\Projects\r2k_bth/src/bluetooth.cpp:26: undefined reference to `BluetoothSerial::read()'
.pio\build\esp32doit-devkit-v1\src\bluetooth.cpp.o: In function `_GLOBAL__sub_D_SerialBth':
C:\Users\Cemal\Documents\PlatformIO\Projects\r2k_bth/src/bluetooth.cpp:8: undefined reference to `BluetoothSerial::~BluetoothSerial()'
collect2.exe: error: ld returned 1 exit status
*** [.pio\build\esp32doit-devkit-v1\firmware.elf] Error 1