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import pmt
import numpy as np
from gnuradio import gr
class blk(gr.sync_block):
def __init__(self):
gr.sync_block.__init__(
self,
name='Phase Lock',
in_sig=[np.complex64],
out_sig=[np.complex64]
)
# we need to keep track of the aboslute number of samples that have
# been processed, because tags have an absolute offset
self.counter: np.uint64 = 0
# because we do block processing, we need to keep track of the last tag
# of the previous block to correct the first values of the next block
self.last = None
def block_phase(self, start, end):
# compute number of samples in block
nsamples = end.offset - start.offset
# unpack pmt values into start and end phase
sphase = pmt.to_python(start.value)
ephase = pmt.to_python(end.value)
# compute frequency offset between start and end
freq = (sphase - ephase) / nsamples
# debugging
print(f"Correction for block of {nsamples:2d} samples is " \
f"phase={sphase: .4f} rad and freq={freq*1e3: .4f} milli rad / sample")
# compute block values
return sphase * np.ones(nsamples) + freq * np.arange(0, nsamples)
def work(self, input_items, output_items):
# FIXME: replace class counter with local variable
# self.counter = self.nitems_written(0)
# nicer aliases
inp = input_items[0]
out = output_items[0]
# read phase tags
is_phase = lambda tag: pmt.to_python(tag.key) == "phase_est"
tags = list(filter(is_phase, self.get_tags_in_window(0, 0, len(inp))))
# debugging
print(f"Processing {len(tags)} tags = {tags[-1].offset - tags[0].offset} " \
f"samples out of {len(inp)} input samples")
# compute "the middle"
enough_samples = lambda pair: ((pair[1].offset - pair[0].offset) > 0)
pairs = list(filter(enough_samples, zip(tags, tags[1:])))
blocks = [ self.block_phase(start, end) for (start, end) in pairs ]
middle = np.concatenate(blocks) if blocks else []
# compute the remainder from the previous call
nfront = tags[0].offset - self.counter
print(f"Processing {nfront} samples at the front of the buffer")
start = self.block_phase(self.last, tags[0])[-nfront:] \
if self.last else np.zeros(nfront)
# compute values at the end
nback = len(inp) - (tags[-1].offset - self.counter)
print(f"Processing {nback} samples at the back of the buffer")
end = np.ones(nback) * pmt.to_python(tags[-1].value)
# compute correction
correction = np.exp(-1j * np.concatenate([start, middle, end]))
length = len(correction)
# write outputs
out[:length] = inp[:length] * correction
self.counter += len(inp)
# save last tag for next call
self.last = tags[-1]
# FIXME: should return `length' but then the last sample is not
# included and self.last does something weird
return len(out)
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