117 lines
4.2 KiB
C
117 lines
4.2 KiB
C
// dump1090, a Mode S messages decoder for RTLSDR devices.
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//
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// Copyright (C) 2012 by Salvatore Sanfilippo <antirez@gmail.com>
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//
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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//
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// * Redistributions in binary form must reproduce the above copyright
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// notice, this list of conditions and the following disclaimer in the
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// documentation and/or other materials provided with the distribution.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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//
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#include "dump1090.h"
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//
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//=========================================================================
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//
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// Input format is : 00:A4:A2:A1:00:B4:B2:B1:00:C4:C2:C1:00:D4:D2:D1
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//
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int ModeAToModeC(unsigned int ModeA)
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{
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unsigned int FiveHundreds = 0;
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unsigned int OneHundreds = 0;
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if ((ModeA & 0xFFFF8889) != 0 || // check zero bits are zero, D1 set is illegal
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(ModeA & 0x000000F0) == 0) { // C1,,C4 cannot be Zero
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return INVALID_ALTITUDE;
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}
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if (ModeA & 0x0010) {OneHundreds ^= 0x007;} // C1
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if (ModeA & 0x0020) {OneHundreds ^= 0x003;} // C2
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if (ModeA & 0x0040) {OneHundreds ^= 0x001;} // C4
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// Remove 7s from OneHundreds (Make 7->5, snd 5->7).
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if ((OneHundreds & 5) == 5) {OneHundreds ^= 2;}
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// Check for invalid codes, only 1 to 5 are valid
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if (OneHundreds > 5) {
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return INVALID_ALTITUDE;
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}
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//if (ModeA & 0x0001) {FiveHundreds ^= 0x1FF;} // D1 never used for altitude
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if (ModeA & 0x0002) {FiveHundreds ^= 0x0FF;} // D2
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if (ModeA & 0x0004) {FiveHundreds ^= 0x07F;} // D4
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if (ModeA & 0x1000) {FiveHundreds ^= 0x03F;} // A1
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if (ModeA & 0x2000) {FiveHundreds ^= 0x01F;} // A2
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if (ModeA & 0x4000) {FiveHundreds ^= 0x00F;} // A4
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if (ModeA & 0x0100) {FiveHundreds ^= 0x007;} // B1
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if (ModeA & 0x0200) {FiveHundreds ^= 0x003;} // B2
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if (ModeA & 0x0400) {FiveHundreds ^= 0x001;} // B4
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// Correct order of OneHundreds.
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if (FiveHundreds & 1) {OneHundreds = 6 - OneHundreds;}
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return ((FiveHundreds * 5) + OneHundreds - 13);
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}
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//
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//=========================================================================
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//
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void decodeModeAMessage(struct modesMessage *mm, int ModeA)
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{
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mm->msgtype = 32; // Valid Mode S DF's are DF-00 to DF-31.
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// so use 32 to indicate Mode A/C
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mm->msgbits = 16; // Fudge up a Mode S style data stream
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mm->msg[0] = mm->verbatim[0] = (ModeA >> 8);
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mm->msg[1] = mm->verbatim[1] = (ModeA);
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// Fudge an address based on Mode A (remove the Ident bit)
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mm->addr = (ModeA & 0x0000FF7F) | MODES_NON_ICAO_ADDRESS;
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// Set the Identity field to ModeA
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mm->squawk = ModeA & 0x7777;
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mm->squawk_valid = 1;
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// Flag ident in flight status
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mm->spi = (ModeA & 0x0080) ? 1 : 0;
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mm->spi_valid = 1;
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// Decode an altitude if this looks like a possible mode C
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if (!mm->spi) {
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int modeC = ModeAToModeC(ModeA);
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if (modeC != INVALID_ALTITUDE) {
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mm->altitude = modeC * 100;
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mm->altitude_unit = UNIT_FEET;
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mm->altitude_source = ALTITUDE_BARO;
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mm->altitude_valid = 1;
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}
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}
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// Not much else we can tell from a Mode A/C reply.
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// Just fudge up a few bits to keep other code happy
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mm->correctedbits = 0;
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}
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//
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// ===================== Mode A/C detection and decoding ===================
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//
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