First commit.

.gitignore

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+*pyc
+*swp
+env

metawatch/protocol.py

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+import struct
+from functools import reduce
+
+# Adapted & Pythonized from pymetawatch by Travis Goodspeed
+class MSPCRC:
+    """Performs a MSP430-compatible CRC-CCIIT."""
+    def __init__(self):
+        self._tab=256*[[]]
+        for i in range(256):
+            crc=0
+            c = i << 8
+            for j in range(8):
+                if (crc ^ c) & 0x8000:
+                    crc = ( crc << 1) ^ 0x1021
+                else:
+                    crc = crc << 1
+                c = c << 1
+                crc = crc & 0xffff
+            self._tab[i] = crc
+
+    def _calculate_crc(self, crc, c):
+        c = c & 0xFF
+        c = self._flip(c)
+
+        tmp = ((crc >> 8) ^ c) & 0xffff
+        crc = (((crc << 8) ^ self._tab[tmp])) & 0xffff
+        return crc
+
+    def checksum_bytes(self, b):
+        """Returns the checksum of a bytes object."""
+        return reduce(self._calculate_crc, b, 0xFFFF)
+
+    def _flip(self,c):
+        """Flips the bit order, because that's how the MSP430 rolls.."""
+        l=[0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15]
+        return ((l[c & 0x0F]) << 4) + l[(c & 0xF0) >> 4]
+
+class OutboundPacket:
+    def _generate(self, _type, options, *args):
+        """Generates a MetaWatch packet based on a given type, options byte and payload bytes."""
+        length = 6 + len(args)
+        data = []
+        data.append(1) # Start Bytes
+        data.append(length)
+        data.append(_type)
+        data.append(options)
+        data += args
+        mspcrc = MSPCRC()
+        crc = mspcrc.checksum_bytes(bytearray(data))
+        self._data = bytes(data) + struct.pack("<H", crc)
+
+    def emit(self, stream):
+        stream.write(self._data)
+        stream.flush()
+
+class GetDeviceType(OutboundPacket):
+    def __init__(self):
+        self._generate(1, 0)
+
+class GetInformationString(OutboundPacket):
+    def __init__(self):
+        self._generate(3, 0)

tests/test_packets.py

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+import unittest
+import io
+
+from metawatch import protocol
+
+class TestPackets(unittest.TestCase):
+    def test_1_crc(self):
+        crc = protocol.MSPCRC()
+        checksum = crc.checksum_bytes(b'\x01\x06\x01\x00')
+        self.assertEqual(checksum, 0xD90B)
+
+    def test_2_basic_outbount_packet(self):
+        p = protocol.OutboundPacket()
+        p._generate(1, 0)
+        self.assertEqual(p._data, b'\x01\x06\x01\x00\x0B\xD9')
+
+    def test_3_packet_emitting(self):
+        p = protocol.OutboundPacket()
+        i = io.BytesIO()
+        p._generate(1, 0)
+        p.emit(i)
+        self.assertEqual(i.getvalue(), b'\x01\x06\x01\x00\x0B\xD9')
+
+    def _test_packet(self, result, klass, *args, **kwargs):
+        p = klass(*args, **kwargs)
+        i = io.BytesIO()
+        p.emit(i)
+        self.assertEqual(i.getvalue(), result)
+
+    def test_4_get_device_type(self):
+        self._test_packet(b'\x01\x06\x01\x00\x0B\xD9', protocol.GetDeviceType)
+
+    def test_5_get_information_string(self):
+        self._test_packet(b'\x01\x06\x03\x00\xc7\xd4', protocol.GetInformationString)