def write_byte(self, addr, val):
        """write_byte(addr, val)

        Perform SMBus Write Byte transaction.
        """
        self._set_addr(addr)
        if SMBUS.i2c_smbus_write_byte(self._fd, ffi.cast("__u8", val)) == -1:
            raise IOError(ffi.errno)
write_byte(addr, val)

        Perform SMBus Write Byte transaction.