From dd795612f0ca0d84e0a17075f8e56d783937bf10 Mon Sep 17 00:00:00 2001
From: Nao Pross <np@0hm.ch>
Date: Thu, 18 Nov 2021 16:11:24 +0100
Subject: Begin frame sync block
---
src/gr-fadingui/python/datasource.py | 3 +-
src/gr-fadingui/python/xor_frame_sync.py | 58 ++++++++++++++++++++++++++++++--
2 files changed, 57 insertions(+), 4 deletions(-)
(limited to 'src/gr-fadingui/python')
diff --git a/src/gr-fadingui/python/datasource.py b/src/gr-fadingui/python/datasource.py
index 764b4d5..ab2f441 100644
--- a/src/gr-fadingui/python/datasource.py
+++ b/src/gr-fadingui/python/datasource.py
@@ -10,7 +10,8 @@ from gnuradio import gr
class datasource(gr.sync_block):
"""
- Loads data from a file choosen in the graphical user interface.
+ Loads data from a file choosen in the graphical user interface, splits into
+ chunks and puts a preamble in front of it(frame).
"""
HEADER_LEN = 11;
diff --git a/src/gr-fadingui/python/xor_frame_sync.py b/src/gr-fadingui/python/xor_frame_sync.py
index 9d9064f..735a031 100644
--- a/src/gr-fadingui/python/xor_frame_sync.py
+++ b/src/gr-fadingui/python/xor_frame_sync.py
@@ -4,24 +4,76 @@
# Copyright 2021 Naoki Pross.
-import numpy
+import numpy as np
+from numpy_ringbuffer import RingBuffer
+
from gnuradio import gr
+
class xor_frame_sync(gr.sync_block):
"""
docstring for block xor_frame_sync
"""
- def __init__(self, sync_pattern):
+ def __init__(self, sync_pattern, buffer_size):
gr.sync_block.__init__(self,
name="xor_frame_sync",
in_sig=[np.byte],
out_sig=[np.byte])
+ # binary pattern to match
+ self.pattern = np.array(sync_pattern, dtype=np.dtype("uint8"))
+ self.nbits = len(sync_pattern)
+
+ # buffer to delay the data
+ self.delay_fifo = RingBuffer(buffer_size, dtype=np.byte)
+
+ # buffers to store cross correlation data
+ self.xcorr = RingBuffer(buffer_size, dtype=np.dtype("uint8"))
+
+ # synchronization state
+ self.synchronized = False
+ self.delay = 0
+
+ def xcorrelation(self):
+ """
+ Compute the binary correlation between the stream and the stored
+ pattern. Binary correlation between two bit vectors is just size of the
+ vector(s) minus the number of bits that differ.
+ """
+ unpacked = np.unpackbits(self.delay_fifo[0])
+ return self.nbits - sum(np.logical_xor(unpacked, self.pattern))
+
def work(self, input_items, output_items):
+ """
+ Process the inputs, that means:
+
+ - Check that the buffer is synchronized, i.e. there is the sync
+ pattern appears every k bits, where k is the size of the packet.
+
+ - If the buffer is not synchronized, compute a binary cross
+ correlation to find how by much the stream should be delayed.
+ """
inp = input_items[0]
out = output_items[0]
- out[:] = inp
+ # Add data to delay buffer
+ self.delay_fifo.appendleft(inp)
+
+ # TODO: check for synchronization, else compute
+
+ # Compute correlation
+ if not self.synchronized:
+ self.xcorr.append(self.xcorrelation())
+
+ peak = np.argmax(self.xcorr)
+ if self.xcorr[peak] != self.nbits:
+ print(f"Warning! XOR correlation is not perfect (peak value = {self.xcorr[peak]})")
+
+ self.delay = peak
+ self.synchronized = True
+
+ # return data with delay
+ out[:] = self.delay_fifo[self.delay]
return len(output_items[0])
--
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