Use AX.25 address field to reduce false alarms
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@ -122,7 +122,7 @@ namespace gr
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*out++ = ((0b1111 & dest_ssid) << 1) | 0b01100000;
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for (i = 0; i < src_addr.length (); i++) {
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*out++ = dest_addr[i] << 1;
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*out++ = src_addr[i] << 1;
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}
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for (; i < AX25_CALLSIGN_MAX_LEN; i++) {
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*out++ = ' ' << 1;
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@ -131,7 +131,7 @@ namespace gr
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* the trailing bit is set to 1.
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* /
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/* FIXME: C bit is set to 0 implicitly */
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*out++ = ((0b1111 & dest_ssid) << 1) | 0b01100001;
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*out++ = ((0b1111 & src_ssid) << 1) | 0b01100001;
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return AX25_MIN_ADDR_LEN;
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}
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@ -133,6 +133,11 @@ namespace gr
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else{
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d_decoded_bits++;
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if(d_decoded_bits == 8) {
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/* Check if the received byte is valid */
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if(!check_byte()) {
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reset_state ();
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return i + 1;
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}
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d_frame_buffer[d_received_bytes] = d_dec_b;
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d_received_bytes++;
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d_decoded_bits = 0;
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@ -226,6 +231,11 @@ namespace gr
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else {
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d_decoded_bits++;
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if (d_decoded_bits == 8) {
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/* Check if the received byte is valid */
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if(!check_byte()) {
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reset_state ();
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return i + 1;
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}
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d_frame_buffer[d_received_bytes] = d_dec_b;
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d_received_bytes++;
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d_decoded_bits = 0;
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@ -338,8 +348,6 @@ namespace gr
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/* First check if the size of the frame is valid */
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if (d_received_bytes < AX25_MIN_ADDR_LEN + sizeof(uint16_t)) {
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message_port_pub (pmt::mp ("failed_pdu"),
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pmt::make_blob (d_frame_buffer, d_received_bytes));
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d_dec_b = 0x0;
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d_shift_reg = 0x0;
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d_decoded_bits = 0;
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@ -417,6 +425,30 @@ namespace gr
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d_dec_b = (d_dec_b >> 1) | (dec_bit << 7);
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}
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/**
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* Checks if a AX.25 decoded byte is valid. This actually can be checked
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* only in the address field, where all fields should have the LS bit
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* set to zero.
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* @returns true if the decoded byte is valid, false otherwise
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*/
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inline bool
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ax25_decoder_bm_impl::check_byte ()
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{
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if(d_received_bytes < AX25_MIN_ADDR_LEN - 1) {
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if(d_dec_b & 0x1) {
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return false;
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}
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}
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else if(d_received_bytes == AX25_MIN_ADDR_LEN - 1) {
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if(d_dec_b & 0x1) {
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return true;
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}
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return false;
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}
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return true;
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}
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int
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ax25_decoder_bm_impl::work (int noutput_items,
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gr_vector_const_void_star &input_items,
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@ -72,6 +72,8 @@ namespace gr
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descramble_and_decode_1b (uint8_t in);
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inline void
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decode_1b (uint8_t in);
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inline bool
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check_byte ();
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public:
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