smbus.py 文件源码

def read_byte_data(self, addr, cmd):
        """Read a single byte from the specified cmd register of the device."""
        assert self._device is not None, 'Bus must be opened before operations are made against it!'
        # Build ctypes values to marshall between ioctl and Python.
        reg = c_uint8(cmd)
        result = c_uint8()
        # Build ioctl request.
        request = make_i2c_rdwr_data([
            (addr, 0, 1, pointer(reg)),             # Write cmd register.
            (addr, I2C_M_RD, 1, pointer(result))    # Read 1 byte as result.
        ])
        # Make ioctl call and return result data.
        ioctl(self._device.fileno(), I2C_RDWR, request)
        return result.value