Class: PWN::SDR::Decoder::Flex::Demod

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

Overview

Streaming FLEX demodulator fed by Base.run_native / Base.run_iq. Per-sample PLL symbol clock, 4-level slicer, full state machine. rubocop:disable Metrics/ClassLength

Instance Method Summary collapse

Constructor Details

#initialize(rate: 48_000) ⇒ Demod

Returns a new instance of Demod.



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# File 'lib/pwn/sdr/decoder/flex.rb', line 46

def initialize(rate: 48_000)
  @rate     = rate.to_f
  @zero     = 0.0
  @env      = 0.0
  @env_sum  = 0.0
  @env_n    = 0
  @phase    = 0.0
  @baud     = 1600
  @last     = 0.0
  @locked   = false
  @symcnt   = [0, 0, 0, 0]
  @state    = :sync1
  @syncbuf  = 0
  @polarity = 0
  @mode     = [1600, 2]
  @fiwcnt   = 0
  @fiw      = 0
  @s2cnt    = 0
  @dcnt     = 0
  @cycle    = 0
  @frame    = 0
  @sync_cw  = 0
  reset_phases
end

Instance Method Details

#feed(samples) ⇒ Object Also known as: feed_audio 



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# File 'lib/pwn/sdr/decoder/flex.rb', line 71

def feed(samples, &)
  phase_max = 100.0 * @rate
  samples.each do |x|
    # DC-offset IIR (10 ms) — only track during Sync-1 hunt
    @zero = ((@zero * (@rate * 0.010)) + x) / ((@rate * 0.010) + 1) if @state == :sync1
    s = x - @zero
    phase_rate = phase_max * @baud / @rate
    ppc = 100.0 * @phase / phase_max
    if @locked
      if @state == :sync1
        @env_sum += s.abs
        @env_n  += 1
        @env     = @env_sum / @env_n
      end
    else
      @env = @env_sum = 0.0
      @env_n = 0
      @baud  = 1600
    end
    # 4-level majority vote over mid-80 % of the symbol period
    if ppc > 10 && ppc < 90
      th = @env * SLICE_TH
      if s.positive?
        s > th ? @symcnt[3] += 1 : @symcnt[2] += 1
      else
        s < -th ? @symcnt[0] += 1 : @symcnt[1] += 1
      end
    end
    # Zero-crossing PLL
    if (@last.negative? && s >= 0) || (@last >= 0 && s.negative?)
      perr = ppc < 50 ? @phase : @phase - phase_max
      @phase -= perr * (@locked ? LOCKED_RATE : UNLOCK_RATE)
      @locked = true
    end
    @last   = s
    @phase += phase_rate
    next unless @phase >= phase_max

    @phase -= phase_max
    sym = @symcnt.index(@symcnt.max)
    @symcnt = [0, 0, 0, 0]
    on_symbol(sym, &)
  end
end