/* unlock the main FMC operation 
, V1.0.0, firmware for GD32F1x0(x=3,5) , V2.0.0, firmware for GD32F1x0(x=3,5,7,9) , V3.0.0, firmware update for GD32F1x0(x=3,5,7,9) */
void fmc_unlock(void)
/* unlock the main FMC operation 
, V1.0.0, firmware for GD32F1x0(x=3,5) , V2.0.0, firmware for GD32F1x0(x=3,5,7,9) , V3.0.0, firmware update for GD32F1x0(x=3,5,7,9) */
void fmc_unlock(void)
{
    if((RESET != (FMC_CTL & FMC_CTL_LK))){
        FMC_KEY = UNLOCK_KEY0;
        FMC_KEY = UNLOCK_KEY1;
    }
}