Class: PWN::SDR::Decoder::GPS::IQTracker

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

Overview

Optional native GNSS-SDR receiver, with a Ruby protocol boundary. Configuration and process lifetime are kept together for auditability.

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(opts) ⇒ IQTracker

rubocop:disable Metrics/ClassLength

Raises:

  • (ArgumentError) 


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# File 'lib/pwn/sdr/decoder/gps.rb', line 106

def initialize(opts)
  @opts = opts
  @file = File.expand_path(opts[:file].to_s)
  raise ArgumentError, 'GPS IQ requires explicit source: :file and a regular file' unless opts[:source] == :file && File.file?(@file)
  raise ArgumentError, 'GPS filename contains configuration delimiters' if @file.match?(/[\r\n;]/)

  @rate = Integer(opts.fetch(:sample_rate, 4_000_000))
  raise ArgumentError, 'GPS sample_rate must be between 2 and 25 Msps' unless @rate.between?(2_000_000, 25_000_000)

  @format = { cs16: ['ishort', 'Ishort_To_Complex', 4], cs8: ['ibyte', 'Ibyte_To_Complex', 2], cf32: ['gr_complex', 'Pass_Through', 8] }[opts.fetch(:iq_format, :cs16)]
  raise ArgumentError, 'GPS iq_format must be :cs16, :cs8 or :cf32' unless @format
  raise ArgumentError, 'GPS IQ file contains an incomplete sample or is empty' if File.empty?(@file) || (File.size(@file) % @format[2]).positive?

  @duration = Float(opts.fetch(:duration, 300))
  raise ArgumentError, 'GPS duration must be finite and positive' unless @duration.finite? && @duration.positive?
end

Class Method Details

.parse_packet(opts = {}) ⇒ Object 



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# File 'lib/pwn/sdr/decoder/gps.rb', line 240

public_class_method def self.parse_packet(opts = {})
  packet = opts[:packet]
  return nil unless packet.bytesize <= 4096

  bytes = packet.bytes
  read_varint = lambda do
    value = 0
    10.times do |index|
      byte = bytes.shift
      raise ArgumentError unless byte

      value |= (byte & 127) << (index * 7)
      return value if byte < 128
    end
    raise ArgumentError
  end
  fields = {}
  until bytes.empty?
    tag = read_varint.call
    key = { 1 => :system, 2 => :signal, 3 => :prn, 4 => :tow_ms, 5 => :nav_message }[tag >> 3]
    case tag & 7
    when 0
      value = read_varint.call
    when 2
      length = read_varint.call
      return nil if length > bytes.length

      value = bytes.shift(length).pack('C*')
    else
      return nil
    end
    fields[key] = value if key
  end
  fields
rescue ArgumentError
  nil
end

Instance Method Details

#configuration(port) ⇒ Object 



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# File 'lib/pwn/sdr/decoder/gps.rb', line 123

def configuration(port)
  {
    'GNSS-SDR.internal_fs_sps' => 2_000_000,
    'ControlThread.wait_for_flowgraph' => false,
    'SignalSource.implementation' => 'File_Signal_Source',
    'SignalSource.filename' => @file,
    'SignalSource.item_type' => @format[0],
    'SignalSource.sampling_frequency' => @rate,
    'SignalSource.samples' => 0,
    'SignalSource.repeat' => false,
    'SignalSource.enable_throttle_control' => true,
    'SignalConditioner.implementation' => 'Signal_Conditioner',
    'DataTypeAdapter.implementation' => @format[1],
    'InputFilter.implementation' => 'Pass_Through',
    'Resampler.implementation' => 'Direct_Resampler',
    'Resampler.sample_freq_in' => @rate,
    'Resampler.sample_freq_out' => 2_000_000,
    'Resampler.item_type' => 'gr_complex',
    'Channels_1C.count' => 8,
    'Channels.in_acquisition' => 1,
    'Channel.signal' => '1C',
    'Acquisition_1C.implementation' => 'GPS_L1_CA_PCPS_Acquisition',
    'Acquisition_1C.item_type' => 'gr_complex',
    'Acquisition_1C.coherent_integration_time_ms' => 1,
    'Acquisition_1C.pfa' => 0.01,
    'Acquisition_1C.doppler_max' => 10_000,
    'Acquisition_1C.doppler_step' => 250,
    'Acquisition_1C.blocking' => true,
    'Tracking_1C.implementation' => 'GPS_L1_CA_DLL_PLL_Tracking',
    'Tracking_1C.item_type' => 'gr_complex',
    'Tracking_1C.pll_bw_hz' => 40.0,
    'Tracking_1C.dll_bw_hz' => 4.0,
    'TelemetryDecoder_1C.implementation' => 'GPS_L1_CA_Telemetry_Decoder',
    'Observables.implementation' => 'Hybrid_Observables',
    'PVT.implementation' => 'RTKLIB_PVT',
    'PVT.positioning_mode' => 'Single',
    'PVT.flag_rtcm_server' => false,
    'PVT.flag_rtcm_tty_port' => false,
    'PVT.flag_nmea_tty_port' => false,
    'NavDataMonitor.enable_monitor' => true,
    'NavDataMonitor.client_addresses' => '127.0.0.1',
    'NavDataMonitor.port' => port
  }.map { |key, value| "#{key}=#{value}" }.unshift('[GNSS-SDR]').join("\n")
end

#run ⇒ Object 



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# File 'lib/pwn/sdr/decoder/gps.rb', line 168

def run
  require 'socket'
  require 'io/wait'
  require 'tmpdir'
  require 'json'
  frames = []
  count = 0
  reason = :eof
  socket = UDPSocket.new
  socket.bind('127.0.0.1', 0)
  Dir.mktmpdir('pwn-gps-') do |directory|
    config = File.join(directory, 'receiver.conf')
    diagnostics = File.join(directory, 'receiver.log')
    File.write(config, configuration(socket.addr[1]))
    begin
      pid = Process.spawn(@opts.fetch(:gnss_sdr, 'gnss-sdr'), "--config_file=#{config}", "--log_dir=#{directory}", in: File::NULL, out: diagnostics, err: %i[child out], chdir: directory, pgroup: true)
    rescue Errno::ENOENT
      raise LoadError, 'GPS IQ tracking requires optional native gnss-sdr (tested 0.0.21); install gnss-sdr or use :lnav_bits'
    end
    deadline = Process.clock_gettime(Process::CLOCK_MONOTONIC) + @duration
    begin
      loop do
        if @opts[:stop]&.call
          reason = :stopped
          break
        end
        if Process.clock_gettime(Process::CLOCK_MONOTONIC) >= deadline
          reason = :duration
          break
        end
        if socket.wait_readable(0.05)
          packet = self.class.parse_packet(packet: socket.recv(4096))
          if packet && packet[:system] == 'G' && packet[:signal] == '1C'
            frame = GPS.decode_monitor(packet)
            if frame
              count += 1
              frames << frame if frames.length < 1000
              @opts[:output]&.write("#{JSON.generate(frame)}\n")
              @opts[:output]&.flush
              @opts[:on_frame]&.call(frame)
            end
          end
          next
        end
        status = Process.waitpid2(pid, Process::WNOHANG)
        next unless status

        pid = nil
        raise IOError, "gnss-sdr failed: #{File.read(diagnostics)[-4000, 4000] || File.read(diagnostics)}" unless status[1].success?

        break
      end
    ensure
      if pid
        Process.kill('TERM', -pid)
        limit = Process.clock_gettime(Process::CLOCK_MONOTONIC) + 2
        until Process.waitpid(pid, Process::WNOHANG)
          if Process.clock_gettime(Process::CLOCK_MONOTONIC) >= limit
            Process.kill('KILL', -pid)
            Process.waitpid(pid)
            break
          end
          sleep 0.02
        end
      end
    end
  end
  { protocol: 'GPS', backend: 'gnss-sdr', frames: frames, frame_count: count, reason: reason, decoded: count.positive? }
ensure
  socket&.close
end