Returns the string message for the given ``error_code``.

        Args:
          cls (JlinkGlobalErrors): the ``JLinkGlobalErrors`` class
          error_code (int): error code to convert

        Returns:
          An error string corresponding to the error code.

        Raises:
          ValueError: if the error code is invalid.

def to_string(cls, error_code):
        """Returns the string message for the given ``error_code``.

        Args:
          cls (JlinkGlobalErrors): the ``JLinkGlobalErrors`` class
          error_code (int): error code to convert

        Returns:
          An error string corresponding to the error code.

        Raises:
          ValueError: if the error code is invalid.
        """
        if error_code == cls.EMU_NO_CONNECTION:
            return 'No connection to emulator.'
        elif error_code == cls.EMU_COMM_ERROR:
            return 'Emulator connection error.'
        elif error_code == cls.DLL_NOT_OPEN:
            return 'DLL has not been opened.  Did you call \'.connect()\'?'
        elif error_code == cls.VCC_FAILURE:
            return 'Target system has no power.'
        elif error_code == cls.INVALID_HANDLE:
            return 'Given file / memory handle is invalid.'
        elif error_code == cls.NO_CPU_FOUND:
            return 'Could not find supported CPU.'
        elif error_code == cls.EMU_FEATURE_UNSUPPORTED:
            return 'Emulator does not support the selected feature.'
        elif error_code == cls.EMU_NO_MEMORY:
            return 'Emulator out of memory.'
        elif error_code == cls.TIF_STATUS_ERROR:
            return 'Target interface error.'
        elif error_code == cls.FLASH_PROG_COMPARE_FAILED:
            return 'Programmed data differs from source data.'
        elif error_code == cls.FLASH_PROG_PROGRAM_FAILED:
            return 'Programming error occured.'
        elif error_code == cls.FLASH_PROG_VERIFY_FAILED:
            return 'Error while verifying programmed data.'
        elif error_code == cls.OPEN_FILE_FAILED:
            return 'Specified file could not be opened.'
        elif error_code == cls.UNKNOWN_FILE_FORMAT:
            return 'File format of selected file is not supported.'
        elif error_code == cls.WRITE_TARGET_MEMORY_FAILED:
            return 'Could not write target memory.'
        elif error_code == cls.DEVICE_FEATURE_NOT_SUPPORTED:
            return 'Feature not supported by connected device.'
        elif error_code == cls.WRONG_USER_CONFIG:
            return 'User configured DLL parameters incorrectly.'
        elif error_code == cls.NO_TARGET_DEVICE_SELECTED:
            return 'User did not specify core to connect to.'
        elif error_code == cls.CPU_IN_LOW_POWER_MODE:
            return 'Target CPU is in low power mode.'
        elif error_code == cls.UNSPECIFIED_ERROR:
            return 'Unspecified error.'
        raise ValueError('Invalid error code: %d' % error_code)