ATTiny88 + TX on PIN_PC1 not working for me :(

[eNovware]

Cannot getting it working on ATtiny88@8MHz(internal) + ATTinyCore 1.5.2 I must do something wrong, here is my code :

#include <Arduino.h> // required for main()
#define TX_PIN PIN_PC1
#include "ATtinySerialOut.hpp"

void setup()
{
      initTXPin();
}

void loop()
{
      writeString("TEST\n");
      delay(1000);
}

Thanks.