Class: PWN::SDR::Decoder::P25::PacketIQ

Inherits:
Object
  • Object
show all
Defined in:
lib/pwn/sdr/decoder/p25.rb

Overview

TIA-102 one-to-three-block TSDU receiver. Protocol tables cross-checked against https://github.com/boatbod/op25/blob/master/op25/gr-op25_repeater/lib/p25p1_fdma.cc C4FM only; no CQPSK, voice, Phase 2 or confirmed 3/4-rate PDUs.

Constant Summary collapse

WORDS = 
[[2, 12, 1, 15], [14, 0, 13, 3], [9, 7, 10, 4], [5, 11, 6, 8]].freeze
INTERLEAVE = 
((0...12).flat_map { |row| [0, 52, 100, 148].flat_map { |base| Array.new(4) { |bit| base + (row * 4) + bit } } } + [48, 49, 50, 51]).freeze

Instance Method Summary collapse

Constructor Details

#initialize(rate:, mode: :tsbk) ⇒ PacketIQ 



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# File 'lib/pwn/sdr/decoder/p25.rb', line 112

def initialize(rate:, mode: :tsbk)
  @mode = mode.to_sym
  @rate = rate.to_f
  @dibits = []
end

Instance Method Details

#feed_dibits(dibits) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/pwn/sdr/decoder/p25.rb', line 154

def feed_dibits(dibits, &)
  raise ArgumentError, 'dibits must be integers 0..3' unless dibits.all? { |d| (0..3).cover?(d) }

  @dibits.concat(dibits)
  while @dibits.length >= 57
    unless @dibits.first(24) == FS_SYMS
      @dibits.shift
      next
    end
    # Status symbol after every 35 data dibits, including sync/NID.
    data = @dibits.each_with_index.reject { |_, i| (i % 36) == 35 }.map(&:first)
    nid = data[24, 32].reduce(0) { |v, d| (v << 2) | d }
    info = checked_nid(nid)
    if info && (info & 15) == 12 && i[pdu all].include?(@mode)
      result = PacketData.parse(data: data, info: info, decoder: method(:decode_block))
      break if result == :incomplete

      if result
        packet, count = result
        [packet].each(&)
        @dibits.shift(count + (count / 35))
      else
        @dibits.shift
      end
      next
    end
    unless info && (info & 15) == 7 && i[tsbk all].include?(@mode)
      @dibits.shift
      next
    end
    packets = []
    incomplete = false
    3.times do |index|
      if data.length < 56 + ((index + 1) * 98)
        incomplete = true
        break
      end
      decoded_block = decode_block(data[56 + (index * 98), 98])
      break unless decoded_block

      bytes, errors = decoded_block
      break unless DSP.crc16(bytes: bytes.first(10), init: 0, xorout: 0xFFFF) == ((bytes[10] << 8) | bytes[11])

      protected = bytes[0].anybits?(0x40)
      payload = bytes[2, 8].pack('C*').unpack1('H*').upcase
      fields = {}
      if !protected && bytes[1].zero? && bytes[0].nobits?(63)
        channel = (bytes[3] << 8) | bytes[4]
        fields = { service_options: bytes[2], channel_id: channel >> 12,
                   channel_number: channel & 0xFFF, talkgroup: (bytes[5] << 8) | bytes[6],
                   source_id: (bytes[7] << 16) | (bytes[8] << 8) | bytes[9] }
      end
      packets << { protocol: 'P25', event: 'tsbk', capability: 'tsdu-tsbk',
                   decoded: true, checksum_verified: true, crc_ok: true,
                   nac: format('%03X', info >> 4), duid: 7, duid_name: 'TSBK',
                   opcode: bytes[0] & 63, manufacturer_id: bytes[1], last_block: bytes[0].anybits?(0x80), block_index: index,
                   protected: protected, encrypted: protected, fec_corrected_bits: errors,
                   payload_hex: protected ? nil : payload,
                   ciphertext_hex: protected ? payload : nil,
                   raw_hex: bytes.pack('C*').unpack1('H*').upcase }.merge(fields)
      break if packets.last[:last_block]
    end
    break if incomplete

    if packets.last && packets.last[:last_block]
      packets.each(&)
      count = 56 + (packets.length * 98)
      @dibits.shift(count + (count / 35))
    else
      @dibits.shift
    end
  end
end

#feed_iq(samples, rate: nil) ⇒ Object

Continuous discriminator and transition-aided clock for centered C4FM. No frequency offset acquisition or CQPSK recovery is claimed.

Raises:

  • (ArgumentError) 


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# File 'lib/pwn/sdr/decoder/p25.rb', line 120

def feed_iq(samples, rate: nil, &)
  @rate = rate.to_f if rate
  raise ArgumentError, 'C4FM requires an integer samples/symbol rate >= 48000' unless @rate >= 48_000 && (@rate % 4800).zero?

  spb = @rate / 4800
  @clock ||= spb / 2
  dibits = []
  samples.each_slice(2) do |re, im|
    next unless im

    if @previous_iq
      pr, pi = @previous_iq
      hz = Math.atan2((im * pr) - (re * pi), (re * pr) + (im * pi)) * @rate / (2 * Math::PI)
      @clock = spb / 2 if @previous_hz && (hz - @previous_hz).abs > 650
      @clock -= 1
      if @clock <= 0
        dibits << (if hz >= 1200
                     1
                   else
                     (if hz >= 0
                        0
                      else
                        (hz > -1200 ? 2 : 3)
                      end)
                   end)
        @clock += spb
      end
      @previous_hz = hz
    end
    @previous_iq = [re, im]
  end
  feed_dibits(dibits, &)
end