1 files changed, 91 insertions, 0 deletions
diff --git a/src/gr-fadingui/python/frame_obj.py b/src/gr-fadingui/python/frame_obj.py
new file mode 100644
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+++ b/src/gr-fadingui/python/frame_obj.py
@@ -0,0 +1,91 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# Copyright 2021 Naoki Pross.
+
+from functools import reduce
+import operator as op
+
+import numpy as np
+from gnuradio import gr
+
+
+class frame_obj:
+    """
+    Frame Object: Contains informations about a data frame.
+
+      -------------------------------------------------------------------------------
+      | Preamble | Padding | ID     | Data Length | Parity | Payload | Padding      |
+      | k bytes  | 1 bit   | 5 bits | 21 bits     | 5 bits |         | if necessary |
+      -------------------------------------------------------------------------------
+                           | (31, 26) Hamming EC code      |
+                           ---------------------------------
+
+    - The preamble is user defined.
+    - The ID (5 bits) + Data length (21 bits) together are a 26 bits, followed
+      by 5 parity bits computed using a (31,26) hamming code.
+
+      This constraints the maximum payload size to 2 MiB and the number IDs to
+      32, i.e. max file size is 64 MiB.
+
+    """
+    def __init__(self, preamble, payload_len):
+        self._preamble = np.array(preamble, dtype=np.uint8)
+
+        self._preamble_len = len(self._preamble)
+        self._payload_len = payload_len
+
+    @property
+    def header_length(self) -> int:
+        """Get header length in bytes"""
+        # 4 is the number of bytes for the hamming part
+        return self._preamble_len + 4
+
+    @property
+    def payload_length(self) -> int:
+        return self._payload_len
+
+    @property
+    def length(self) -> int:
+        """Get frame lenght in bytes"""
+        # 8 is the size of the hamming ECC part + 1 bit
+        return self.header_length + self.payload_length
+
+    @property
+    def preamble(self):
+        """Get preamble"""
+        return self._preamble
+
+    def parity(self, bits):
+        """Compute the 5 parity bits for an unpacked array of 26 bits"""
+        assert(len(bits) == 26)
+        # FIXME: does not work
+        # return np.matmul(bits, gen) % 2
+        return np.array([0, 0, 0, 0, 0])
+
+    def make(self, idv, data_len, data):
+        """Make a frame"""
+        # get lower 4 bits of idv
+        idv_bits = np.unpackbits([np.uint8(idv)])[:5]
+
+        # get lower 22 bits of data_len
+        data_len_bytes = list(map(np.uint8, data_len.to_bytes(4, byteorder='little')))
+        data_len_bits = np.unpackbits(data_len_bytes)[:21]
+
+        # compute 5 parity bits
+        metadata = np.concatenate([idv_bits, data_len_bits])
+        parity_bits = self.parity(metadata)
+
+        # add padding
+        hamming_bits = np.concatenate([[0], metadata, parity_bits])
+        assert(len(hamming_bits) == 32)
+
+        # pack 32 bits into 4 bytes and add the rest
+        hamming = np.packbits(hamming_bits)
+        return np.concatenate([self.preamble, hamming, data])
+
+    def syndrome(self, bits):
+        """Compute the syndrome (check Hamming code) for an unpacked array of 31 bits"""
+        assert(len(bits) == 31)
+        return reduce(op.xor, [i for i, bit in enumerate(bits) if bit])
+