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https://github.com/greatscottgadgets/hackrf.git
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409acbc3c9
Co-authored-by: mndza <diego.hdmp@gmail.com> Co-authored-by: Martin Ling <martin-git@earth.li> Co-authored-by: Antoine van Gelder <antoine@greatscottgadgets.com>
59 lines
1.7 KiB
Python
59 lines
1.7 KiB
Python
#
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# This file is part of Glasgow Interface Explorer.
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#
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# Copyright (c) 2025 Glasgow Interface Explorer contributors.
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# SPDX-License-Identifier: BSD-0-Clause
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from amaranth import *
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__all__ = ["LinearFeedbackShiftRegister"]
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class LinearFeedbackShiftRegister(Elaboratable):
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"""A linear feedback shift register. Useful for generating long pseudorandom sequences with
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a minimal amount of logic.
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Use ``CEInserter`` and ``ResetInserter`` transformers to control the LFSR.
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:param degree:
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Width of register, in bits.
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:type degree: int
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:param taps:
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Feedback taps, with bits numbered starting at 1 (i.e. polynomial degrees).
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:type taps: list of int
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:param reset:
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Initial value loaded into the register. Must be non-zero, or only zeroes will be
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generated.
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:type reset: int
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"""
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def __init__(self, degree, taps, init=1):
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assert init != 0
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self.degree = degree
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self.taps = taps
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self.init = init
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self.value = Signal(degree, init=init)
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def elaborate(self, platform):
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m = Module()
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feedback = 0
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for tap in self.taps:
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feedback ^= (self.value >> (tap - 1)) & 1
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m.d.sync += self.value.eq((self.value << 1) | feedback)
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return m
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def generate(self):
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"""Generate every distinct value the LFSR will take."""
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value = self.init
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mask = (1 << self.degree) - 1
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while True:
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yield value
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feedback = 0
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for tap in self.taps:
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feedback ^= (value >> (tap - 1)) & 1
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value = ((value << 1) & mask) | feedback
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if value == self.init:
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break |