Merge pull request #1 from adafruit/struct

Add i2c_struct class for arbitrary structure register.

Author: tannewt

adafruit_register/i2c_struct.py

@@ -0,0 +1,49 @@
+# The MIT License (MIT)
+#
+# Copyright (c) 2016 Adafruit Industries
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+import ustruct
+
+
+class Struct:
+    """
+    Arbitrary structure register that is readable and writeable.
+
+    Values are tuples that map to the values 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:])
+
+    def __set__(self, obj, value):
+        struct.pack_into(self.format, self.buffer, 1, *value)
+        with obj.i2c_device:
+            obj.i2c_device.writeto(self.buffer)