Class: PWN::SDR::Decoder::POCSAG::BitStream

Inherits:
Object
  • Object
show all
Defined in:
lib/pwn/sdr/decoder/pocsag.rb

Overview

Incremental framing retains partial codewords and messages across transport chunks and batch sync words. A terminator emits immediately.

Instance Method Summary collapse

Constructor Details

#initialize(baud:) ⇒ BitStream

Returns a new instance of BitStream.



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# File 'lib/pwn/sdr/decoder/pocsag.rb', line 31

def initialize(baud:)
  @baud = baud
  @bits = []
  @word_index = nil
  @pending = nil
end

Instance Method Details

#feed(bits, &emit) ⇒ Object 



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# File 'lib/pwn/sdr/decoder/pocsag.rb', line 38

def feed(bits, &emit)
  @bits.concat(bits)
  loop do
    if @word_index.nil? || @word_index == 16
      idx = DSP.find_sync(bits: @bits, pattern: FSC, width: 32, max_err: 2)
      unless idx
        @bits.shift([@bits.length - 31, 0].max)
        break
      end
      @bits.shift(idx + 32)
      @word_index = 0
    end
    break if @bits.length < 32

    cw = DSP.bits_to_int(bits: @bits.shift(32))
    cw = POCSAG.correct_word(word: cw)
    unless cw
      @pending = nil
      @word_index += 1
      next
    end
    if cw == IDLE_CW
      emit_pending(&emit)
    elsif cw.nobits?(0x80000000)
      emit_pending(&emit)
      @pending = { ric: (((cw >> 13) & 0x3FFFF) << 3) | (@word_index / 2),
                   func: (cw >> 11) & 3, msg_words: [] }
    elsif @pending
      @pending[:msg_words] << ((cw >> 11) & 0xFFFFF)
    end
    @word_index += 1
  end
end

#flush ⇒ Object 



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# File 'lib/pwn/sdr/decoder/pocsag.rb', line 72

def flush(&)
  @pending = nil unless @bits.empty?
  return unless @pending

  emit_pending(&)
end