allow multibyte write-then-read and is backcompatible if you pass in …

…a byte instead of a bytearray

Adafruit_PureIO/smbus.py

@@ -204,13 +204,25 @@ def read_i2c_block_data(self, addr, cmd, length=32):
         """
         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)
+
+        # convert register into bytearray
+        if not isinstance(cmd, (bytes, bytearray)):
+            reg = cmd  # backup
+            cmd = bytearray(1)
+            cmd[0] = reg
+
+        cmdstring = create_string_buffer(len(cmd))
+        for i in range(len(cmd)):
+            cmdstring[i] = cmd[i]
+
         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.
-        ])
+            (addr, 0,        len(cmd), cast(cmdstring, POINTER(c_uint8))),             # 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!