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Remove the 2MHz demodulator.

Browse source 
Now that the 2.4MHz demodulator does 3A/C there's no real reason
to keep the old demodulator around.
This commit is contained in:
Oliver Jowett 2016-05-31 12:23:58 +01:00
parent b8dc3973d1
commit 8f82e61f17
10 changed files with 6 additions and 953 deletions
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2
Makefile
View file

@ -43,7 +43,7 @@ all: dump1090 view1090
dump1090.o: CFLAGS += `pkg-config --cflags librtlsdr`
dump1090: dump1090.o anet.o interactive.o mode_ac.o mode_s.o net_io.o crc.o demod_2000.o demod_2400.o stats.o cpr.o icao_filter.o track.o util.o convert.o $(COMPAT)
dump1090: dump1090.o anet.o interactive.o mode_ac.o mode_s.o net_io.o crc.o demod_2400.o stats.o cpr.o icao_filter.o track.o util.o convert.o $(COMPAT)
$(CC) -g -o $@ $^ $(LIBS) $(LIBS_RTL) $(LDFLAGS)
view1090: view1090.o anet.o interactive.o mode_ac.o mode_s.o net_io.o crc.o stats.o cpr.o icao_filter.o track.o util.o $(COMPAT)

3
debian/config-template vendored
View file

@ -31,9 +31,6 @@ GAIN=
# RTLSDR frequency correction in PPM
PPM=
# If yes, enable sampling at 2.4MHz. Otherwise, 2.0MHz is used.
OVERSAMPLE=
#
# Decoding options
#

2
debian/dump1090-mutability.config vendored
View file

@ -23,7 +23,6 @@ if [ -e $CONFIGFILE ]; then
db_set $NAME/rtlsdr-device "$DEVICE"
db_set $NAME/rtlsdr-gain "$GAIN"
db_set $NAME/rtlsdr-ppm "$PPM"
db_set_yn $NAME/rtlsdr-oversample "$OVERSAMPLE"
db_set_yn $NAME/decode-fixcrc "$FIX_CRC"
db_set $NAME/decode-lat "$LAT"
@ -199,7 +198,6 @@ db_go || true; db_get $NAME/auto-start; if [ "$RET" = "true" ]; then
# only if a real device was chosen:
db_input_verify medium $NAME/rtlsdr-gain is_valid_gain || true
db_input_verify medium $NAME/rtlsdr-ppm is_signed_int || true
db_input low $NAME/rtlsdr-oversample || true
fi
db_input low $NAME/decode-fix-crc || true

1
debian/dump1090-mutability.init vendored
View file

@ -56,7 +56,6 @@ case "x$GAIN" in
*) ARGS="$ARGS --gain $GAIN" ;;
esac
if [ -n "$PPM" ]; then ARGS="$ARGS --ppm $PPM"; fi
if [ "x$OVERSAMPLE" = "xyes" ]; then ARGS="$ARGS --oversample"; fi
# decoder:
if [ "x$FIX_CRC" = "xyes" ]; then ARGS="$ARGS --fix"; fi

1
debian/dump1090-mutability.postinst vendored
View file

@ -75,7 +75,6 @@ case "$1" in
subvar rtlsdr-device DEVICE
subvar rtlsdr-gain GAIN
subvar rtlsdr-ppm PPM
subvar_yn rtlsdr-oversample OVERSAMPLE
subvar_yn decode-fixcrc FIX_CRC
subvar decode-lat LAT
subvar decode-lon LON

8
debian/dump1090-mutability.templates vendored
View file

@ -53,14 +53,6 @@ Description: RTL-SDR frequency correction, in PPM:
Type: string
Default: 0
Template: dump1090-mutability/rtlsdr-oversample
Description: Enable oversampling at 2.4MHz?
Originally, dump1090 would decode incoming signals by sampling at 2MHz. Newer
versions also support sampling at 2.4MHz. This may increase the number of
decodable messages, but takes slightly more CPU and is not as well tested.
Type: boolean
Default: true
Template: dump1090-mutability/decode-fixcrc
Description: Fix detected CRC errors?
dump1090 can fix unambiguous single-bit CRC errors detected in received

891
demod_2000.c
View file

@ -1,891 +0,0 @@
// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// demod_2000.c: 2MHz Mode S demodulator.
//
// Copyright (c) 2014,2015 Oliver Jowett <oliver@mutability.co.uk>
//
// This file is free software: you may copy, redistribute and/or modify it
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 2 of the License, or (at your
// option) any later version.
//
// This file is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
// This file incorporates work covered by the following copyright and
// permission notice:
//
// Copyright (C) 2012 by Salvatore Sanfilippo <antirez@gmail.com>
//
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//
// * Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#include "dump1090.h"
// Mode S 2.0MHz demodulator
//
// ===================== Mode A/C detection and decoding ===================
//
//
// This table is used to build the Mode A/C variable called ModeABits.Each
// bit period is inspected, and if it's value exceeds the threshold limit,
// then the value in this table is or-ed into ModeABits.
//
// At the end of message processing, ModeABits will be the decoded ModeA value.
//
// We can also flag noise in bits that should be zeros - the xx bits. Noise in
// these bits cause bits (31-16) in ModeABits to be set. Then at the end of message
// processing we can test for errors by looking at these bits.
//
uint32_t ModeABitTable[24] = {
0x00000000, // F1 = 1
0x00000010, // C1
0x00001000, // A1
0x00000020, // C2
0x00002000, // A2
0x00000040, // C4
0x00004000, // A4
0x40000000, // xx = 0 Set bit 30 if we see this high
0x00000100, // B1
0x00000001, // D1
0x00000200, // B2
0x00000002, // D2
0x00000400, // B4
0x00000004, // D4
0x00000000, // F2 = 1
0x08000000, // xx = 0 Set bit 27 if we see this high
0x04000000, // xx = 0 Set bit 26 if we see this high
0x00000080, // SPI
0x02000000, // xx = 0 Set bit 25 if we see this high
0x01000000, // xx = 0 Set bit 24 if we see this high
0x00800000, // xx = 0 Set bit 23 if we see this high
0x00400000, // xx = 0 Set bit 22 if we see this high
0x00200000, // xx = 0 Set bit 21 if we see this high
0x00100000, // xx = 0 Set bit 20 if we see this high
};
//
// This table is used to produce an error variable called ModeAErrs.Each
// inter-bit period is inspected, and if it's value falls outside of the
// expected range, then the value in this table is or-ed into ModeAErrs.
//
// At the end of message processing, ModeAErrs will indicate if we saw
// any inter-bit anomolies, and the bits that are set will show which
// bits had them.
//
uint32_t ModeAMidTable[24] = {
0x80000000, // F1 = 1 Set bit 31 if we see F1_C1 error
0x00000010, // C1 Set bit 4 if we see C1_A1 error
0x00001000, // A1 Set bit 12 if we see A1_C2 error
0x00000020, // C2 Set bit 5 if we see C2_A2 error
0x00002000, // A2 Set bit 13 if we see A2_C4 error
0x00000040, // C4 Set bit 6 if we see C3_A4 error
0x00004000, // A4 Set bit 14 if we see A4_xx error
0x40000000, // xx = 0 Set bit 30 if we see xx_B1 error
0x00000100, // B1 Set bit 8 if we see B1_D1 error
0x00000001, // D1 Set bit 0 if we see D1_B2 error
0x00000200, // B2 Set bit 9 if we see B2_D2 error
0x00000002, // D2 Set bit 1 if we see D2_B4 error
0x00000400, // B4 Set bit 10 if we see B4_D4 error
0x00000004, // D4 Set bit 2 if we see D4_F2 error
0x20000000, // F2 = 1 Set bit 29 if we see F2_xx error
0x08000000, // xx = 0 Set bit 27 if we see xx_xx error
0x04000000, // xx = 0 Set bit 26 if we see xx_SPI error
0x00000080, // SPI Set bit 15 if we see SPI_xx error
0x02000000, // xx = 0 Set bit 25 if we see xx_xx error
0x01000000, // xx = 0 Set bit 24 if we see xx_xx error
0x00800000, // xx = 0 Set bit 23 if we see xx_xx error
0x00400000, // xx = 0 Set bit 22 if we see xx_xx error
0x00200000, // xx = 0 Set bit 21 if we see xx_xx error
0x00100000, // xx = 0 Set bit 20 if we see xx_xx error
};
//
// The "off air" format is,,
// _F1_C1_A1_C2_A2_C4_A4_xx_B1_D1_B2_D2_B4_D4_F2_xx_xx_SPI_
//
// Bit spacing is 1.45uS, with 0.45uS high, and 1.00us low. This is a problem
// because we ase sampling at 2Mhz (500nS) so we are below Nyquist.
//
// The bit spacings are..
// F1 : 0.00,
// 1.45, 2.90, 4.35, 5.80, 7.25, 8.70,
// X : 10.15,
// : 11.60, 13.05, 14.50, 15.95, 17.40, 18.85,
// F2 : 20.30,
// X : 21.75, 23.20, 24.65
//
// This equates to the following sample point centers at 2Mhz.
// [ 0.0],
// [ 2.9], [ 5.8], [ 8.7], [11.6], [14.5], [17.4],
// [20.3],
// [23.2], [26.1], [29.0], [31.9], [34.8], [37.7]
// [40.6]
// [43.5], [46.4], [49.3]
//
// We know that this is a supposed to be a binary stream, so the signal
// should either be a 1 or a 0. Therefore, any energy above the noise level
// in two adjacent samples must be from the same pulse, so we can simply
// add the values together..
//
int detectModeA(uint16_t *m, struct modesMessage *mm)
{
int j, lastBitWasOne;
int ModeABits = 0;
int ModeAErrs = 0;
int byte, bit;
int thisSample, lastBit, lastSpace = 0;
int m0, m1, m2, m3, mPhase;
int n0, n1, n2 ,n3;
int F1_sig, F1_noise;
int F2_sig, F2_noise;
int fSig, fNoise, fLevel, fLoLo;
// m[0] contains the energy from 0 -> 499 nS
// m[1] contains the energy from 500 -> 999 nS
// m[2] contains the energy from 1000 -> 1499 nS
// m[3] contains the energy from 1500 -> 1999 nS
//
// We are looking for a Frame bit (F1) whose width is 450nS, followed by
// 1000nS of quiet.
//
// The width of the frame bit is 450nS, which is 90% of our sample rate.
// Therefore, in an ideal world, all the energy for the frame bit will be
// in a single sample, preceeded by (at least) one zero, and followed by
// two zeros, Best case we can look for ...
//
// 0 - 1 - 0 - 0
//
// However, our samples are not phase aligned, so some of the energy from
// each bit could be spread over two consecutive samples. Worst case is
// that we sample half in one bit, and half in the next. In that case,
// we're looking for
//
// 0 - 0.5 - 0.5 - 0.
m0 = m[0]; m1 = m[1];
if (m0 >= m1) // m1 *must* be bigger than m0 for this to be F1
{return (0);}
m2 = m[2]; m3 = m[3];
//
// if (m2 <= m0), then assume the sample bob on (Phase == 0), so don't look at m3
if ((m2 <= m0) || (m2 < m3))
{m3 = m2; m2 = m0;}
if ( (m3 >= m1) // m1 must be bigger than m3
|| (m0 > m2) // m2 can be equal to m0 if ( 0,1,0,0 )
|| (m3 > m2) ) // m2 can be equal to m3 if ( 0,1,0,0 )
{return (0);}
// m0 = noise
// m1 = noise + (signal * X))
// m2 = noise + (signal * (1-X))
// m3 = noise
//
// Hence, assuming all 4 samples have similar amounts of noise in them
// signal = (m1 + m2) - ((m0 + m3) * 2)
// noise = (m0 + m3) / 2
//
F1_sig = (m1 + m2) - ((m0 + m3) << 1);
F1_noise = (m0 + m3) >> 1;
if ( (F1_sig < MODEAC_MSG_SQUELCH_LEVEL) // minimum required F1 signal amplitude
|| (F1_sig < (F1_noise << 2)) ) // minimum allowable Sig/Noise ratio 4:1
{return (0);}
// If we get here then we have a potential F1, so look for an equally valid F2 20.3uS later
//
// Our F1 is centered somewhere between samples m[1] and m[2]. We can guestimate where F2 is
// by comparing the ratio of m1 and m2, and adding on 20.3 uS (40.6 samples)
//
mPhase = ((m2 * 20) / (m1 + m2));
byte = (mPhase + 812) / 20;
n0 = m[byte++]; n1 = m[byte++];
if (n0 >= n1) // n1 *must* be bigger than n0 for this to be F2
{return (0);}
n2 = m[byte++];
//
// if the sample bob on (Phase == 0), don't look at n3
//
if ((mPhase + 812) % 20)
{n3 = m[byte++];}
else
{n3 = n2; n2 = n0;}
if ( (n3 >= n1) // n1 must be bigger than n3
|| (n0 > n2) // n2 can be equal to n0 ( 0,1,0,0 )
|| (n3 > n2) ) // n2 can be equal to n3 ( 0,1,0,0 )
{return (0);}
F2_sig = (n1 + n2) - ((n0 + n3) << 1);
F2_noise = (n0 + n3) >> 1;
if ( (F2_sig < MODEAC_MSG_SQUELCH_LEVEL) // minimum required F2 signal amplitude
|| (F2_sig < (F2_noise << 2)) ) // maximum allowable Sig/Noise ratio 4:1
{return (0);}
fSig = (F1_sig + F2_sig) >> 1;
fNoise = (F1_noise + F2_noise) >> 1;
fLoLo = fNoise + (fSig >> 2); // 1/2
fLevel = fNoise + (fSig >> 1);
lastBitWasOne = 1;
lastBit = F1_sig;
//
// Now step by a half ModeA bit, 0.725nS, which is 1.45 samples, which is 29/20
// No need to do bit 0 because we've already selected it as a valid F1
// Do several bits past the SPI to increase error rejection
//
for (j = 1, mPhase += 29; j < 48; mPhase += 29, j ++)
{
byte = 1 + (mPhase / 20);
thisSample = m[byte] - fNoise;
if (mPhase % 20) // If the bit is split over two samples...
{thisSample += (m[byte+1] - fNoise);} // add in the second sample's energy
// If we're calculating a space value
if (j & 1)
{lastSpace = thisSample;}
else
{// We're calculating a new bit value
bit = j >> 1;
if (thisSample >= fLevel)
{// We're calculating a new bit value, and its a one
ModeABits |= ModeABitTable[bit--]; // or in the correct bit
if (lastBitWasOne)
{ // This bit is one, last bit was one, so check the last space is somewhere less than one
if ( (lastSpace >= (thisSample>>1)) || (lastSpace >= lastBit) )
{ModeAErrs |= ModeAMidTable[bit];}
}
else
{// This bit,is one, last bit was zero, so check the last space is somewhere less than one
if (lastSpace >= (thisSample >> 1))
{ModeAErrs |= ModeAMidTable[bit];}
}
lastBitWasOne = 1;
}
else
{// We're calculating a new bit value, and its a zero
if (lastBitWasOne)
{ // This bit is zero, last bit was one, so check the last space is somewhere in between
if (lastSpace >= lastBit)
{ModeAErrs |= ModeAMidTable[bit];}
}
else
{// This bit,is zero, last bit was zero, so check the last space is zero too
if (lastSpace >= fLoLo)
{ModeAErrs |= ModeAMidTable[bit];}
}
lastBitWasOne = 0;
}
lastBit = (thisSample >> 1);
}
}
//
// Output format is : 00:A4:A2:A1:00:B4:B2:B1:00:C4:C2:C1:00:D4:D2:D1
//
if ((ModeABits < 3) || (ModeABits & 0xFFFF8808) || (ModeAErrs) )
{return (ModeABits = 0);}
mm->signalLevel = (fSig + fNoise) * (fSig + fNoise) / MAX_POWER;
return ModeABits;
}
// ============================== Debugging =================================
//
// Helper function for dumpMagnitudeVector().
// It prints a single bar used to display raw signals.
//
// Since every magnitude sample is between 0-255, the function uses
// up to 63 characters for every bar. Every character represents
// a length of 4, 3, 2, 1, specifically:
//
// "O" is 4
// "o" is 3
// "-" is 2
// "." is 1
//
static void dumpMagnitudeBar(int index, int magnitude) {
char *set = " .-o";
char buf[256];
int div = magnitude / 256 / 4;
int rem = magnitude / 256 % 4;
memset(buf,'O',div);
buf[div] = set[rem];
buf[div+1] = '\0';
if (index >= 0)
printf("[%.3d] |%-66s 0x%04X\n", index, buf, magnitude);
else
printf("[%.2d] |%-66s 0x%04X\n", index, buf, magnitude);
}
//
//=========================================================================
//
// Display an ASCII-art alike graphical representation of the undecoded
// message as a magnitude signal.
//
// The message starts at the specified offset in the "m" buffer.
// The function will display enough data to cover a short 56 bit message.
//
// If possible a few samples before the start of the messsage are included
// for context.
//
static void dumpMagnitudeVector(uint16_t *m, uint32_t offset) {
uint32_t padding = 5; // Show a few samples before the actual start.
uint32_t start = (offset < padding) ? 0 : offset-padding;
uint32_t end = offset + (MODES_PREAMBLE_SAMPLES)+(MODES_SHORT_MSG_SAMPLES) - 1;
uint32_t j;
for (j = start; j <= end; j++) {
dumpMagnitudeBar(j-offset, m[j]);
}
}
//
//=========================================================================
//
// Produce a raw representation of the message as a Javascript file
// loadable by debug.html.
//
static void dumpRawMessageJS(char *descr, unsigned char *msg,
uint16_t *m, uint32_t offset, struct errorinfo *ei)
{
int padding = 5; // Show a few samples before the actual start.
int start = offset - padding;
int end = offset + (MODES_PREAMBLE_SAMPLES)+(MODES_LONG_MSG_SAMPLES) - 1;
FILE *fp;
int j;
if ((fp = fopen("frames.js","a")) == NULL) {
fprintf(stderr, "Error opening frames.js: %s\n", strerror(errno));
exit(1);
}
fprintf(fp,"frames.push({\"descr\": \"%s\", \"mag\": [", descr);
for (j = start; j <= end; j++) {
fprintf(fp,"%d", j < 0 ? 0 : m[j]);
if (j != end) fprintf(fp,",");
}
fprintf(fp, "], ");
for (j = 0; j < MODES_MAX_BITERRORS; ++j)
fprintf(fp,"\"fix%d\": %d, ", j, ei->bit[j]);
fprintf(fp, "\"bits\": %d, \"hex\": \"", modesMessageLenByType(msg[0]>>3));
for (j = 0; j < MODES_LONG_MSG_BYTES; j++)
fprintf(fp,"\\x%02x",msg[j]);
fprintf(fp,"\"});\n");
fclose(fp);
}
//
//=========================================================================
//
// This is a wrapper for dumpMagnitudeVector() that also show the message
// in hex format with an additional description.
//
// descr is the additional message to show to describe the dump.
// msg points to the decoded message
// m is the original magnitude vector
// offset is the offset where the message starts
//
// The function also produces the Javascript file used by debug.html to
// display packets in a graphical format if the Javascript output was
// enabled.
//
static void dumpRawMessage(char *descr, unsigned char *msg, uint16_t *m, uint32_t offset) {
int j;
int msgtype = msg[0] >> 3;
struct errorinfo *ei = NULL;
if (msgtype == 17) {
int len = modesMessageLenByType(msgtype);
uint32_t csum = modesChecksum(msg, len);
ei = modesChecksumDiagnose(csum, len);
}
if (Modes.debug & MODES_DEBUG_JS) {
dumpRawMessageJS(descr, msg, m, offset, ei);
return;
}
printf("\n--- %s\n ", descr);
for (j = 0; j < MODES_LONG_MSG_BYTES; j++) {
printf("%02x",msg[j]);
if (j == MODES_SHORT_MSG_BYTES-1) printf(" ... ");
}
printf(" (DF %d, Fixable: %d)\n", msgtype, ei ? ei->errors : 0);
dumpMagnitudeVector(m,offset);
printf("---\n\n");
}
//
//=========================================================================
//
// Return -1 if the message is out of fase left-side
// Return 1 if the message is out of fase right-size
// Return 0 if the message is not particularly out of phase.
//
// Note: this function will access pPreamble[-1], so the caller should make sure to
// call it only if we are not at the start of the current buffer
//
static int detectOutOfPhase(uint16_t *pPreamble) {
if (pPreamble[ 3] > pPreamble[2]/3) return 1;
if (pPreamble[10] > pPreamble[9]/3) return 1;
if (pPreamble[ 6] > pPreamble[7]/3) return -1;
if (pPreamble[-1] > pPreamble[1]/3) return -1;
return 0;
}
static uint16_t clamped_scale(uint16_t v, uint16_t scale) {
uint32_t scaled = (uint32_t)v * scale / 16384;
if (scaled > 65535) return 65535;
return (uint16_t) scaled;
}
// This function decides whether we are sampling early or late,
// and by approximately how much, by looking at the energy in
// preamble bits before and after the expected pulse locations.
//
// It then deals with one sample pair at a time, comparing samples
// to make a decision about the bit value. Based on this decision it
// modifies the sample value of the *adjacent* sample which will
// contain some of the energy from the bit we just inspected.
//
// pPayload[0] should be the start of the preamble,
// pPayload[-1 .. MODES_PREAMBLE_SAMPLES + MODES_LONG_MSG_SAMPLES - 1] should be accessible.
// pPayload[MODES_PREAMBLE_SAMPLES .. MODES_PREAMBLE_SAMPLES + MODES_LONG_MSG_SAMPLES - 1] will be updated.
static void applyPhaseCorrection(uint16_t *pPayload) {
int j;
// we expect 1 bits at 0, 2, 7, 9
// and 0 bits at -1, 1, 3, 4, 5, 6, 8, 10, 11, 12, 13, 14
// use bits -1,6 for early detection (bit 0/7 arrived a little early, our sample period starts after the bit phase so we include some of the next bit)
// use bits 3,10 for late detection (bit 2/9 arrived a little late, our sample period starts before the bit phase so we include some of the last bit)
uint32_t onTime = (pPayload[0] + pPayload[2] + pPayload[7] + pPayload[9]);
uint32_t early = (pPayload[-1] + pPayload[6]) << 1;
uint32_t late = (pPayload[3] + pPayload[10]) << 1;
if (onTime == 0 && early == 0 && late == 0) {
// Blah, can't do anything with this, avoid a divide-by-zero
return;
}
if (early > late) {
// Our sample period starts late and so includes some of the next bit.
uint16_t scaleUp = 16384 + 16384 * early / (early + onTime); // 1 + early / (early+onTime)
uint16_t scaleDown = 16384 - 16384 * early / (early + onTime); // 1 - early / (early+onTime)
// trailing bits are 0; final data sample will be a bit low.
pPayload[MODES_PREAMBLE_SAMPLES + MODES_LONG_MSG_SAMPLES - 1] =
clamped_scale(pPayload[MODES_PREAMBLE_SAMPLES + MODES_LONG_MSG_SAMPLES - 1], scaleUp);
for (j = MODES_PREAMBLE_SAMPLES + MODES_LONG_MSG_SAMPLES - 2; j > MODES_PREAMBLE_SAMPLES; j -= 2) {
if (pPayload[j] > pPayload[j+1]) {
// x [1 0] y
// x overlapped with the "1" bit and is slightly high
pPayload[j-1] = clamped_scale(pPayload[j-1], scaleDown);
} else {
// x [0 1] y
// x overlapped with the "0" bit and is slightly low
pPayload[j-1] = clamped_scale(pPayload[j-1], scaleUp);
}
}
} else {
// Our sample period starts early and so includes some of the previous bit.
uint16_t scaleUp = 16384 + 16384 * late / (late + onTime); // 1 + late / (late+onTime)
uint16_t scaleDown = 16384 - 16384 * late / (late + onTime); // 1 - late / (late+onTime)
// leading bits are 0; first data sample will be a bit low.
pPayload[MODES_PREAMBLE_SAMPLES] = clamped_scale(pPayload[MODES_PREAMBLE_SAMPLES], scaleUp);
for (j = MODES_PREAMBLE_SAMPLES; j < MODES_PREAMBLE_SAMPLES + MODES_LONG_MSG_SAMPLES - 2; j += 2) {
if (pPayload[j] > pPayload[j+1]) {
// x [1 0] y
// y overlapped with the "0" bit and is slightly low
pPayload[j+2] = clamped_scale(pPayload[j+2], scaleUp);
} else {
// x [0 1] y
// y overlapped with the "1" bit and is slightly high
pPayload[j+2] = clamped_scale(pPayload[j+2], scaleDown);
}
}
}
}
//
//=========================================================================
//
// Detect a Mode S messages inside the magnitude buffer pointed by 'm' and of
// size 'mlen' bytes. Every detected Mode S message is convert it into a
// stream of bits and passed to the function to display it.
//
void demodulate2000(struct mag_buf *mag) {
struct modesMessage mm;
unsigned char msg[MODES_LONG_MSG_BYTES], *pMsg;
uint16_t aux[MODES_PREAMBLE_SAMPLES+MODES_LONG_MSG_SAMPLES+1];
uint32_t j;
int use_correction = 0;
unsigned mlen = mag->length;
uint16_t *m = mag->data;
memset(&mm, 0, sizeof(mm));
// The Mode S preamble is made of impulses of 0.5 microseconds at
// the following time offsets:
//
// 0 - 0.5 usec: first impulse.
// 1.0 - 1.5 usec: second impulse.
// 3.5 - 4 usec: third impulse.
// 4.5 - 5 usec: last impulse.
//
// Since we are sampling at 2 Mhz every sample in our magnitude vector
// is 0.5 usec, so the preamble will look like this, assuming there is
// an impulse at offset 0 in the array:
//
// 0 -----------------
// 1 -
// 2 ------------------
// 3 --
// 4 -
// 5 --
// 6 -
// 7 ------------------
// 8 --
// 9 -------------------
//
for (j = 0; j < mlen; j++) {
int high, i, errors, errors56, errorsTy;
uint16_t *pPreamble, *pPayload, *pPtr;
uint8_t theByte, theErrs;
int msglen, scanlen;
uint32_t sigLevel, noiseLevel;
uint16_t snr;
int message_ok;
pPreamble = &m[j];
pPayload = &m[j+MODES_PREAMBLE_SAMPLES];
// Rather than clear the whole mm structure, just clear the parts which are required. The clear
// is required for every bit of the input stream, and we don't want to be memset-ing the whole
// modesMessage structure two million times per second if we don't have to..
mm.bFlags =
mm.correctedbits = 0;
if (!use_correction) // This is not a re-try with phase correction
{ // so try to find a new preamble
if (Modes.mode_ac)
{
int ModeA = detectModeA(pPreamble, &mm);
if (ModeA) // We have found a valid ModeA/C in the data
{
mm.timestampMsg = mag->sampleTimestamp + ((j+1) * 6);
// compute message receive time as block-start-time + difference in the 12MHz clock
mm.sysTimestampMsg = mag->sysTimestamp; // start of block time
mm.sysTimestampMsg.tv_nsec += receiveclock_ns_elapsed(mag->sampleTimestamp, mm.timestampMsg);
normalize_timespec(&mm.sysTimestampMsg);
// Decode the received message
decodeModeAMessage(&mm, ModeA);
// Pass data to the next layer
useModesMessage(&mm);
j += MODEAC_MSG_SAMPLES;
Modes.stats_current.demod_modeac++;
continue;
}
}
// First check of relations between the first 10 samples
// representing a valid preamble. We don't even investigate further
// if this simple test is not passed
if (!(pPreamble[0] > pPreamble[1] &&
pPreamble[1] < pPreamble[2] &&
pPreamble[2] > pPreamble[3] &&
pPreamble[3] < pPreamble[0] &&
pPreamble[4] < pPreamble[0] &&
pPreamble[5] < pPreamble[0] &&
pPreamble[6] < pPreamble[0] &&
pPreamble[7] > pPreamble[8] &&
pPreamble[8] < pPreamble[9] &&
pPreamble[9] > pPreamble[6]))
{
if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
*pPreamble > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Unexpected ratio among first 10 samples", msg, m, j);
continue;
}
// The samples between the two spikes must be < than the average
// of the high spikes level. We don't test bits too near to
// the high levels as signals can be out of phase so part of the
// energy can be in the near samples
high = (pPreamble[0] + pPreamble[2] + pPreamble[7] + pPreamble[9]) / 6;
if (pPreamble[4] >= high ||
pPreamble[5] >= high)
{
if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
*pPreamble > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Too high level in samples between 3 and 6", msg, m, j);
continue;
}
// Similarly samples in the range 11-14 must be low, as it is the
// space between the preamble and real data. Again we don't test
// bits too near to high levels, see above
if (pPreamble[11] >= high ||
pPreamble[12] >= high ||
pPreamble[13] >= high ||
pPreamble[14] >= high)
{
if (Modes.debug & MODES_DEBUG_NOPREAMBLE &&
*pPreamble > MODES_DEBUG_NOPREAMBLE_LEVEL)
dumpRawMessage("Too high level in samples between 10 and 15", msg, m, j);
continue;
}
Modes.stats_current.demod_preambles++;
}
else {
// If the previous attempt with this message failed, retry using
// magnitude correction
// Make a copy of the Payload, and phase correct the copy
memcpy(aux, &pPreamble[-1], sizeof(aux));
applyPhaseCorrection(&aux[1]);
pPayload = &aux[1 + MODES_PREAMBLE_SAMPLES];
// TODO ... apply other kind of corrections
}
// Decode all the next 112 bits, regardless of the actual message
// size. We'll check the actual message type later
pMsg = &msg[0];
pPtr = pPayload;
theByte = 0;
theErrs = 0; errorsTy = 0;
errors = 0; errors56 = 0;
// We should have 4 'bits' of 0/1 and 1/0 samples in the preamble,
// so include these in the signal strength
sigLevel = pPreamble[0] + pPreamble[2] + pPreamble[7] + pPreamble[9];
noiseLevel = pPreamble[1] + pPreamble[3] + pPreamble[4] + pPreamble[6] + pPreamble[8];
msglen = scanlen = MODES_LONG_MSG_BITS;
for (i = 0; i < scanlen; i++) {
uint32_t a = *pPtr++;
uint32_t b = *pPtr++;
if (a > b)
{theByte |= 1; if (i < 56) { sigLevel += a; noiseLevel += b; }}
else if (a < b)
{/*theByte |= 0;*/ if (i < 56) { sigLevel += b; noiseLevel += a; }}
else {
if (i < 56) { sigLevel += a; noiseLevel += a; }
if (i >= MODES_SHORT_MSG_BITS) //(a == b), and we're in the long part of a frame
{errors++; /*theByte |= 0;*/}
else if (i >= 5) //(a == b), and we're in the short part of a frame
{scanlen = MODES_LONG_MSG_BITS; errors56 = ++errors;/*theByte |= 0;*/}
else if (i) //(a == b), and we're in the message type part of a frame
{errorsTy = errors56 = ++errors; theErrs |= 1; /*theByte |= 0;*/}
else //(a == b), and we're in the first bit of the message type part of a frame
{errorsTy = errors56 = ++errors; theErrs |= 1; theByte |= 1;}
}
if ((i & 7) == 7)
{*pMsg++ = theByte;}
else if (i == 4) {
msglen = modesMessageLenByType(theByte);
if (errors == 0)
{scanlen = msglen;}
}
theByte = theByte << 1;
if (i < 7)
{theErrs = theErrs << 1;}
// If we've exceeded the permissible number of encoding errors, abandon ship now
if (errors > MODES_MSG_ENCODER_ERRS) {
if (i < MODES_SHORT_MSG_BITS) {
msglen = 0;
} else if ((errorsTy == 1) && (theErrs == 0x80)) {
// If we only saw one error in the first bit of the byte of the frame, then it's possible
// we guessed wrongly about the value of the bit. We may be able to correct it by guessing
// the other way.
//
// We guessed a '1' at bit 7, which is the DF length bit == 112 Bits.
// Inverting bit 7 will change the message type from a long to a short.
// Invert the bit, cross your fingers and carry on.
msglen = MODES_SHORT_MSG_BITS;
msg[0] ^= theErrs; errorsTy = 0;
errors = errors56; // revert to the number of errors prior to bit 56
} else if (i < MODES_LONG_MSG_BITS) {
msglen = MODES_SHORT_MSG_BITS;
errors = errors56;
} else {
msglen = MODES_LONG_MSG_BITS;
}
break;
}
}
// Ensure msglen is consistent with the DF type
if (msglen > 0) {
i = modesMessageLenByType(msg[0] >> 3);
if (msglen > i) {msglen = i;}
else if (msglen < i) {msglen = 0;}
}
//
// If we guessed at any of the bits in the DF type field, then look to see if our guess was sensible.
// Do this by looking to see if the original guess results in the DF type being one of the ICAO defined
// message types. If it isn't then toggle the guessed bit and see if this new value is ICAO defined.
// if the new value is ICAO defined, then update it in our message.
if ((msglen) && (errorsTy == 1) && (theErrs & 0x78)) {
// We guessed at one (and only one) of the message type bits. See if our guess is "likely"
// to be correct by comparing the DF against a list of known good DF's
int thisDF = ((theByte = msg[0]) >> 3) & 0x1f;
uint32_t validDFbits = 0x017F0831; // One bit per 32 possible DF's. Set bits 0,4,5,11,16.17.18.19,20,21,22,24
uint32_t thisDFbit = (1 << thisDF);
if (0 == (validDFbits & thisDFbit)) {
// The current DF is not ICAO defined, so is probably an errors.
// Toggle the bit we guessed at and see if the resultant DF is more likely
theByte ^= theErrs;
thisDF = (theByte >> 3) & 0x1f;
thisDFbit = (1 << thisDF);
// if this DF any more likely?
if (validDFbits & thisDFbit) {
// Yep, more likely, so update the main message
msg[0] = theByte;
errors--; // decrease the error count so we attempt to use the modified DF.
}
}
}
// snr = 5 * 20log10(sigLevel / noiseLevel) (in units of 0.2dB)
// = 100log10(sigLevel) - 100log10(noiseLevel)
while (sigLevel > 65535 || noiseLevel > 65535) {
sigLevel >>= 1;
noiseLevel >>= 1;
}
snr = Modes.log10lut[sigLevel] - Modes.log10lut[noiseLevel];
// When we reach this point, if error is small, and the signal strength is large enough
// we may have a Mode S message on our hands. It may still be broken and the CRC may not
// be correct, but this can be handled by the next layer.
if ( (msglen)
&& ((2 * snr) > (int) (MODES_MSG_SQUELCH_DB * 10))
&& (errors <= MODES_MSG_ENCODER_ERRS) ) {
int result;
// Set initial mm structure details
mm.timestampMsg = mag->sampleTimestamp + (j*6);
// compute message receive time as block-start-time + difference in the 12MHz clock
mm.sysTimestampMsg = mag->sysTimestamp; // start of block time
mm.sysTimestampMsg.tv_nsec += receiveclock_ns_elapsed(mag->sampleTimestamp, mm.timestampMsg);
normalize_timespec(&mm.sysTimestampMsg);
mm.signalLevel = (365.0*60 + sigLevel + noiseLevel) * (365.0*60 + sigLevel + noiseLevel) / MAX_POWER / 60 / 60;
// Decode the received message
result = decodeModesMessage(&mm, msg);
if (result < 0) {
message_ok = 0;
if (result == -1)
Modes.stats_current.demod_rejected_unknown_icao++;
else
Modes.stats_current.demod_rejected_bad++;
} else {
message_ok = 1;
Modes.stats_current.demod_accepted[mm.correctedbits]++;
}
// Update statistics
// Output debug mode info if needed
if (use_correction) {
if (Modes.debug & MODES_DEBUG_DEMOD)
dumpRawMessage("Demodulated with 0 errors", msg, m, j);
else if (Modes.debug & MODES_DEBUG_BADCRC &&
mm.msgtype == 17 &&
(!message_ok || mm.correctedbits > 0))
dumpRawMessage("Decoded with bad CRC", msg, m, j);
else if (Modes.debug & MODES_DEBUG_GOODCRC &&
message_ok &&
mm.correctedbits == 0)
dumpRawMessage("Decoded with good CRC", msg, m, j);
}
// Skip this message if we are sure it's fine
if (message_ok) {
j += (MODES_PREAMBLE_US+msglen)*2 - 1;
// Pass data to the next layer
useModesMessage(&mm);
}
} else {
message_ok = 0;
if (Modes.debug & MODES_DEBUG_DEMODERR && use_correction) {
printf("The following message has %d demod errors\n", errors);
dumpRawMessage("Demodulated with errors", msg, m, j);
}
}
// Retry with phase correction if necessary and possible.
if ((!message_ok || mm.correctedbits > 0) && !use_correction && j && detectOutOfPhase(pPreamble)) {
use_correction = 1; j--;
} else {
use_correction = 0;
}
}
}

29
demod_2000.h
View file

@ -1,29 +0,0 @@
// Part of dump1090, a Mode S message decoder for RTLSDR devices.
//
// demod_2000.h: 2MHz Mode S demodulator prototypes.
//
// Copyright (c) 2014,2015 Oliver Jowett <oliver@mutability.co.uk>
//
// This file is free software: you may copy, redistribute and/or modify it
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 2 of the License, or (at your
// option) any later version.
//
// This file is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
#ifndef DUMP1090_DEMOD_2000_H
#define DUMP1090_DEMOD_2000_H
#include <stdint.h>
struct mag_buf;
void demodulate2000(struct mag_buf *mag);
#endif

18
dump1090.c
View file

@ -167,10 +167,7 @@ void modesInit(void) {
pthread_mutex_init(&Modes.data_mutex,NULL);
pthread_cond_init(&Modes.data_cond,NULL);
if (Modes.oversample)
Modes.sample_rate = 2400000.0;
else
Modes.sample_rate = 2000000.0;
Modes.sample_rate = 2400000.0;
// Allocate the various buffers used by Modes
Modes.trailing_samples = (MODES_PREAMBLE_US + MODES_LONG_MSG_BITS + 16) * 1e-6 * Modes.sample_rate;
@ -720,7 +717,6 @@ void showHelp(void) {
"--write-json <dir> Periodically write json output to <dir> (for serving by a separate webserver)\n"
"--write-json-every <t> Write json output every t seconds (default 1)\n"
"--json-location-accuracy <n> Accuracy of receiver location in json metadata: 0=no location, 1=approximate, 2=exact\n"
"--oversample Use the 2.4MHz demodulator\n"
"--dcfilter Apply a 1Hz DC filter to input data (requires lots more CPU)\n"
"--help Show this help\n"
"\n"
@ -1077,7 +1073,7 @@ int main(int argc, char **argv) {
Modes.interactive = 1;
Modes.interactive_rtl1090 = 1;
} else if (!strcmp(argv[j],"--oversample")) {
Modes.oversample = 1;
// Ignored
} else if (!strcmp(argv[j], "--html-dir") && more) {
Modes.html_dir = strdup(argv[++j]);
#ifndef _WIN32
@ -1204,13 +1200,9 @@ int main(int argc, char **argv) {
// stuff at the same time.
pthread_mutex_unlock(&Modes.data_mutex);
if (Modes.oversample) {
demodulate2400(buf);
if (Modes.mode_ac) {
demodulate2400AC(buf);
}
} else {
demodulate2000(buf);
demodulate2400(buf);
if (Modes.mode_ac) {
demodulate2400AC(buf);
}
Modes.stats_current.samples_processed += buf->length;

4
dump1090.h
View file

@ -90,8 +90,6 @@ typedef struct rtlsdr_dev rtlsdr_dev_t;
// ============================= #defines ===============================
#define MODES_DEFAULT_PPM 52
#define MODES_DEFAULT_RATE 2000000
#define MODES_OVERSAMPLE_RATE 2400000
#define MODES_DEFAULT_FREQ 1090000000
#define MODES_DEFAULT_WIDTH 1000
#define MODES_DEFAULT_HEIGHT 700
@ -211,7 +209,6 @@ typedef struct rtlsdr_dev rtlsdr_dev_t;
#include "anet.h"
#include "net_io.h"
#include "crc.h"
#include "demod_2000.h"
#include "demod_2400.h"
#include "stats.h"
#include "cpr.h"
@ -280,7 +277,6 @@ struct { // Internal state
// Configuration
char *filename; // Input form file, --ifile option
int oversample;
int nfix_crc; // Number of crc bit error(s) to correct
int check_crc; // Only display messages with good CRC
int raw; // Raw output format