Add UnaryStruct to i2c_struct, simplified single value struct register.

Author: tdicola

adafruit_register/i2c_struct.py

@@ -47,3 +47,29 @@ def __set__(self, obj, value):
         ustruct.pack_into(self.format, self.buffer, 1, *value)
         with obj.i2c_device:
             obj.i2c_device.writeto(self.buffer)
+
+class UnaryStruct:
+    """
+    Arbitrary single value structure register that is readable and writeable.
+
+    Values map to the first value in the defined struct.  See struct
+    module documentation for struct format string and its possible value types.
+
+    :param int register_address: The register address to read the bit from
+    :param type struct_format: The struct format string for this register.
+    """
+    def __init__(self, register_address, struct_format):
+        self.format = struct_format
+        self.buffer = bytearray(1+ustruct.calcsize(self.format))
+        self.buffer[0] = register_address
+
+    def __get__(self, obj, objtype=None):
+        with obj.i2c_device:
+            obj.i2c_device.writeto(self.buffer, end=1, stop=False)
+            obj.i2c_device.readfrom_into(self.buffer, start=1)
+        return ustruct.unpack_from(self.format, memoryview(self.buffer)[1:])[0]
+
+    def __set__(self, obj, value):
+        ustruct.pack_into(self.format, self.buffer, 1, value)
+        with obj.i2c_device:
+            obj.i2c_device.writeto(self.buffer)