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#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2021 Naoki Pross.
import numpy as np
from numpy_ringbuffer import RingBuffer
from gnuradio import gr
from fadingui.logger import get_logger
log = get_logger("xor_frame_sync")
class xor_frame_sync(gr.sync_block):
"""
Performs a frame synchronization by XOR matching a preamble bit sequence
"""
def __init__(self, sync_pattern, buffer_size):
# TODO: buffer size should be in packets
gr.sync_block.__init__(self,
name="xor_frame_sync",
in_sig=[np.byte],
out_sig=[np.byte])
# binary pattern to match
self.pattern = sync_pattern
self.nbytes = len(self.pattern)
self.pattern_bits = np.unpackbits(np.array(self.pattern, dtype=np.uint8))[::-1]
self.nbits = len(self.pattern_bits)
log.debug(f"Loaded pattern {self.pattern_bits} length={self.nbits}")
assert(self.nbits % 8 == 0)
# packed buffer to delay the data
self.delaybuf = RingBuffer(buffer_size, dtype=np.uint8)
self.delay = 0
log.debug(f"Created delay ring buffer of size {self.delaybuf.maxlen}")
# unpacked buffer to compute correlation values, initially filled with zeros
self.corrbuf = RingBuffer(self.nbits, dtype=np.uint8)
self.corrbuf.extend(np.zeros(self.corrbuf.maxlen))
# synchronization state
self.synchronized = False
def xcorrelation(self, v):
"""
Compute the binary correlations between the stored pattern and
correlation buffer, while shifting v into the buffer.
Binary correlation between two bit vectors is just size of the
vector(s) minus the number of bits that differ.
@return: Number of bits of v that were shifted into the buffer
when the correlation matched. If no match is found
the return value is None.
"""
# this could be much faster with shifts, bitwise or and xor
# but this should do alright for the moment
v_bits = np.unpackbits(np.array(v, dtype=np.uint8))
for bitnr, b in enumerate(v_bits):
self.corrbuf.appendleft(b)
if (np.bitwise_xor(self.corrbuf, self.pattern_bits) == 0).all():
return bitnr
# no cross correlation found
return None
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 much the stream should be delayed.
"""
# array of samples, growing index = forward in time
inp = input_items[0]
inp_len = len(inp)
if not self.synchronized:
if inp_len > self.delaybuf.maxlen:
log.error("Input is bigger than delay buffer")
# FIXME: Makes the QA hang for some reason
raise NotImplemented
# create space for new samples in the delay buffer
self.delaybuf.extendleft(np.zeros(inp_len))
# Add values and while processing
for bytenr, value in enumerate(inp):
# save value in the buffer
# FIXME: this is wrong, it should be in reverse order
self.delaybuf.appendleft(value)
# compute the cross correlation
bitnr = self.xcorrelation(value)
if bitnr is not None:
# correlation was found
delay_bits = (bitnr - 7)
delay_bytes = 8 * (bytenr -1)
log.debug(f"Synchronized with delay_bytes={delay_bytes} delay_bits={delay_bits}")
# FIXME: add bit delay
self.delay = delay_bytes
self.synchronized = True
# Not aligned to bytes
if delay_bits != 0:
log.error("Not implemented: byte unaligned delay")
self.synchronized = False
self.delay = 0
# FIXME: Makes the QA hang for some reason
# raise NotImplemented
# stop processing inputs
break
if not self.synchronized:
log.warning(f"Processed {inp_len} samples but could not synchronize")
else:
self.delaybuf.extendleft(inp)
# return data with delay
out = output_items[0]
# FIXME: this is also wrong
out[:] = self.delaybuf[:len(out)]
inptmp = np.array(inp[:12], dtype=np.uint8)
inphex = np.array(list(map(hex, inptmp)))
log.debug(f"inp={inptmp}")
log.debug(f"inp={inphex}")
# outtmp = np.array(out[:12], dtype=np.uint8)
# log.debug(f"out={outtmp}")
return len(out)
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