Add support for unsigned24 and integer24

Unsigned24 was inspired by 659899d,
but kept a little simpler. I also added the signed version.

Signed-off-by: Greter Raffael <[email protected]>

Author: raffi-g

canopen/objectdictionary/__init__.py

@@ -10,6 +10,7 @@
 import logging
 
 from canopen.objectdictionary.datatypes import *
+from canopen.objectdictionary.datatypes_24bit import Integer24, Unsigned24
 
 logger = logging.getLogger(__name__)
 
@@ -277,10 +278,12 @@ class ODVariable:
         BOOLEAN: struct.Struct("?"),
         INTEGER8: struct.Struct("b"),
         INTEGER16: struct.Struct("<h"),
+        INTEGER24: Integer24(),
         INTEGER32: struct.Struct("<l"),
         INTEGER64: struct.Struct("<q"),
         UNSIGNED8: struct.Struct("B"),
         UNSIGNED16: struct.Struct("<H"),
+        UNSIGNED24: Unsigned24(),
         UNSIGNED32: struct.Struct("<L"),
         UNSIGNED64: struct.Struct("<Q"),
         REAL32: struct.Struct("<f"),

canopen/objectdictionary/datatypes.py

@@ -11,12 +11,14 @@
 OCTET_STRING = 0xA
 UNICODE_STRING = 0xB
 DOMAIN = 0xF
+INTEGER24 = 0x10
 REAL64 = 0x11
 INTEGER64 = 0x15
+UNSIGNED24 = 0x16
 UNSIGNED64 = 0x1B
 
-SIGNED_TYPES = (INTEGER8, INTEGER16, INTEGER32, INTEGER64)
-UNSIGNED_TYPES = (UNSIGNED8, UNSIGNED16, UNSIGNED32, UNSIGNED64)
+SIGNED_TYPES = (INTEGER8, INTEGER16, INTEGER24, INTEGER32, INTEGER64)
+UNSIGNED_TYPES = (UNSIGNED8, UNSIGNED16, UNSIGNED24, UNSIGNED32, UNSIGNED64)
 INTEGER_TYPES = SIGNED_TYPES + UNSIGNED_TYPES
 FLOAT_TYPES = (REAL32, REAL64)
 NUMBER_TYPES = INTEGER_TYPES + FLOAT_TYPES

canopen/objectdictionary/datatypes_24bit.py

@@ -0,0 +1,33 @@
+import struct
+
+
+class Unsigned24:
+    def __init__(self):
+        self.__st = struct.Struct("<L")
+
+    def unpack(self, __buffer):
+        return self.__st.unpack(__buffer + b'\x00')
+
+    def pack(self, *v):
+        return self.__st.pack(*v)[:3]
+
+    @property
+    def size(self):
+        return 3
+
+
+class Integer24:
+    def __init__(self):
+        self.__st = struct.Struct("<l")
+
+    def unpack(self, __buffer):
+        mask = 0x80
+        neg = (__buffer[2] & mask) > 0
+        return self.__st.unpack(__buffer + (b'\xff' if neg else b'\x00'))
+
+    def pack(self, *v):
+        return self.__st.pack(*v)[:3]
+
+    @property
+    def size(self):
+        return 3