smbus.py 文件源码

def read_i2c_block_data(self, addr, cmd, length=32):
        """Perform a read from the specified cmd register of device.  Length number
        of bytes (default of 32) will be read and returned as a bytearray.
        """
        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 = create_string_buffer(length)
        # Build ioctl request.
        request = make_i2c_rdwr_data([
            (addr, 0, 1, pointer(reg)),             # Write cmd register.
            (addr, I2C_M_RD, length, cast(result, POINTER(c_uint8)))   # Read data.
        ])
        # Make ioctl call and return result data.
        ioctl(self._device.fileno(), I2C_RDWR, request)
        return bytearray(result.raw)  # Use .raw instead of .value which will stop at a null byte!