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Adding demodulator for ARGOS 4 PTT-VLD-A4 (A4-SS-TER-SP-0079-CNES) #12

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Adding demodulator for ARGOS 4 PTT-VLD-A4 (A4-SS-TER-SP-0079-CNES) #12

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ad3f37f
Adding the ARGOS 4 PTT-VLD-A4 demodulator
PaulZC Oct 25, 2020
4a49914
Update readme.md
PaulZC Oct 25, 2020
206fa07
Added the short example from A4-SS-TER-SP-0079-CNES
PaulZC Oct 25, 2020
cb48383
Removing the invert option.
PaulZC Oct 26, 2020
a939954
Adding carrier deviation and manchester resync as args
PaulZC Oct 28, 2020
91fbc0f
Calculate the normalization factor based on the whole file - not just…
PaulZC Oct 31, 2020
7e90134
Whitespace corrections
PaulZC Oct 31, 2020
2f395a2
Corrected how the symbols are written to the raw output file
PaulZC Oct 31, 2020
7302474
Found the 0 that was stopping the inverse sync word from being found
PaulZC Oct 31, 2020
aeb536b
Adding the ARGOS 4 VLD Long example
PaulZC Nov 1, 2020
013aa6d
Updates after I corrected the TCXO voltage
PaulZC Jan 31, 2021
aff780e
Merge remote-tracking branch 'upstream/master'
PaulZC Jan 31, 2021
f547bb6
Removing extra files that accidentally crept into ARGOSdemod
PaulZC Jan 31, 2021
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70 changes: 35 additions & 35 deletions ARGOS4VLDdemod/ByteSync.c
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Original file line number Diff line number Diff line change
Expand Up @@ -21,10 +21,10 @@ int FindSyncWords(unsigned char *bitStreamIn, double *bitStreamInTime, unsigned
static int oldest = 0, syncIndicator, frameByteIdx, packetShiftFlag=0, bitIdx;
static unsigned char zero=0, one=1;
static unsigned char byte=0;

int packetsFound=0;
unsigned long idx;

if(firstTime == 1)
{
firstTime = 0;
Expand All @@ -37,26 +37,26 @@ int FindSyncWords(unsigned char *bitStreamIn, double *bitStreamInTime, unsigned
}
memset(historyBufferCirc, 48, sizeof(char) * syncWordLength);
}

//loop through samples

for(idx = 0; idx < nSamples; idx++)
{
//Enter this loop if we found a syncword last time around
if(packetShiftFlag == 1)
{
if(bitStreamIn[idx]=='0')
if(bitStreamIn[idx]=='0')
{
byte = byte << 1; //This is a zero, just shift
byte = byte | zero;
}
else
{
byte = byte << 1; //This is a one, set the bit then shift
byte = byte << 1; //This is a one, set the bit then shift
byte = byte | one;
}
bitIdx++;

bitIdx++;
if(bitIdx > 7)
{
//minorFrame[frameByteIdx]=byte;
Expand All @@ -65,40 +65,40 @@ int FindSyncWords(unsigned char *bitStreamIn, double *bitStreamInTime, unsigned
byte = 0;
bitIdx = 0;
frameByteIdx++;
if(frameByteIdx > 8)
if(frameByteIdx > 24)
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Remind me what this change does ?

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Ah, yes. It took me a while to find where the longer ARGOS 4 VLD Long messages were being truncated - and its there. That change just lets 24 bytes of data through instead of 8. Actually I think we only need 18 bytes, not 24. It might be nice to add the expected message length as an arg?

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yeah, good call. The best way would be to detect the end of the packet.... not so easy though!!

Is there a payload length byte we could read in to make a guess on??

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Yes, indeed:
The sync is 24 bits: 0xAC5353
The two bits after that define the length. If they are 0b00 then the total number of encoded data bits after that is 68. If the two length bits are 0b11 then 3*68 encoded data bits follow.
Note: this is only true for ARGOS 4 VLD. The other PTT formats use quite different length fields.
image

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Ah, but... The encoding process reduces the 68 bits down to 45. So, the true answer, in terms of how many bits to process, is:

  • 0b00 indicates that 45 bits follow
  • 0b11 indicates that 3*45 bits follow

{
packetShiftFlag = 0;
fprintf(packetFile,"\n");
printf("\n");
}
}
}
//overwrite oldest bit in cir buffer with newest bit
historyBufferCirc[oldest] = bitStreamIn[idx];
}

//overwrite oldest bit in cir buffer with newest bit
historyBufferCirc[oldest] = bitStreamIn[idx];
//printf("h[%d]=%c\n",oldest, historyBufferCirc[oldest]);
syncIndicator = 1; //set to 1 to enable, any other to disable
//Look for syncword
for (idx2 = 0; idx2 < syncWordLength; idx2++)


syncIndicator = 1; //set to 1 to enable, any other to disable

//Look for syncword
for (idx2 = 0; idx2 < syncWordLength; idx2++)
{
//compare syncword bytes to appropriate circular buffer bytes

if (syncWord[idx2] != historyBufferCirc[(oldest + idx2 + 1) % syncWordLength])
{
syncIndicator = 0;
break;
}
}

if(syncIndicator == 1 && packetShiftFlag == 0)
{
fprintf(packetFile,"%.5f ",bitStreamInTime[idx]);
//fprintf(packetFile,"%.2X ",0b11100010);
//fprintf(packetFile,"%.2X ",0b11110000);

printf("%.5f ",bitStreamInTime[idx]);
frameByteIdx = 2;
packetShiftFlag = 1;
Expand All @@ -108,29 +108,29 @@ int FindSyncWords(unsigned char *bitStreamIn, double *bitStreamInTime, unsigned
zero = 0;
one = 1;
//bitIdx=;
}
}

//Look for Inverse Syncword
syncIndicator = 0; //set to 1 to enable, any other to disable
for (idx2 = 0; idx2 < syncWordLength; idx2++)
syncIndicator = 1; //set to 1 to enable, any other to disable
for (idx2 = 0; idx2 < syncWordLength; idx2++)
{
//compare syncword bytes to appropriate circular buffer bytes
//printf("sw[%d] == hst[%d] , %c == %c, ", idx2,(oldest + idx2 + 1) % syncWordLength,syncWord[idx2],historyBufferCirc[(oldest + idx2) % syncWordLength]);

if (syncWord[idx2] == historyBufferCirc[(oldest + idx2 + 1) % syncWordLength])
{
syncIndicator = 0;
//printf("NO\n\n");
break;
}
}
}

if(syncIndicator == 1 && packetShiftFlag == 0)
{
fprintf(packetFile,"%.5fi ",bitStreamInTime[idx]);
//fprintf(packetFile,"%.2X ",0b11100010);
//fprintf(packetFile,"%.2X ",0b11110000);

printf("\t%.5fi ",bitStreamInTime[idx]);
frameByteIdx = 2;
packetShiftFlag = 1;
Expand All @@ -140,10 +140,10 @@ int FindSyncWords(unsigned char *bitStreamIn, double *bitStreamInTime, unsigned
zero = 1;
one = 0;
//bitIdx=;
}
//advance oldest bit pointer
}

//advance oldest bit pointer
oldest = (oldest + 1) % syncWordLength;
}
return packetsFound;
}
return packetsFound;
}
2 changes: 1 addition & 1 deletion ARGOS4VLDdemod/RAW_Plotter.py
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,7 @@
break

fig, ax = plt.subplots()
ax.plot(x, y)
ax.plot(x, y, 'o-')

ax.set(xlabel='sample', ylabel='signal',
title=sys.argv[1])
Expand Down
Binary file modified ARGOS4VLDdemod/demodARGOS.exe
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28 changes: 14 additions & 14 deletions ARGOS4VLDdemod/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -86,7 +86,7 @@ int main(int argc, char **argv)
double dspMaxCarrierDeviation = DSP_MAX_CARRIER_DEVIATION;

//unsigned int CheckSum1=0, CheckSum2=0, CheckSum3=0;
int nFrames=0, totalFrames=0,c;
int nFrames=0, totalFrames=0, c;

unsigned char *dataStreamBits=NULL;
char *inFileName=NULL;
Expand Down Expand Up @@ -303,25 +303,25 @@ int main(int argc, char **argv)
//nSymbols = MMClockRecovery(dataStreamReal, waveDataTime, nSamples, dataStreamSymbols, Fs, 3, 0.15);
nSymbols = GardenerClockRecovery(dataStreamReal, waveDataTime, nSamples, dataStreamSymbols, Fs, DSP_BAUD, DSP_GDNR_ERR_LIM, DSP_GDNR_GAIN);

if(outputRawFiles == 1)
{
for(idx=0; idx < nSymbols; idx++)
{
fwrite(&dataStreamSymbols[idx],sizeof(double),1,rawOutFilePtr);
}
}

//nBits = ManchesterDecode(dataStreamSymbols, waveDataTime, nSymbols, dataStreamBits, DSP_MCHSTR_RESYNC_LVL);
nBits = ManchesterDecode(dataStreamSymbols, waveDataTime, nSymbols, dataStreamBits, dspManchesterResyncLevel);

// if(outputRawFiles == 1)
// {
// for(idx=0; idx < nBits; idx++)
// for(idx=0; idx < nSymbols; idx++)
// {
// fwrite(&dataStreamBits[idx],sizeof(char),1,rawOutFilePtr);
// fwrite(&dataStreamSymbols[idx],sizeof(double),1,rawOutFilePtr);
// }
// }

//nBits = ManchesterDecode(dataStreamSymbols, waveDataTime, nSymbols, dataStreamBits, DSP_MCHSTR_RESYNC_LVL);
nBits = ManchesterDecode(dataStreamSymbols, waveDataTime, nSymbols, dataStreamBits, dspManchesterResyncLevel);

if(outputRawFiles == 1)
{
for(idx=0; idx < nBits; idx++)
{
fwrite(&dataStreamBits[idx],sizeof(char),1,rawOutFilePtr);
}
}

// There's no need to invert the data. FindSyncWords automatically checks for the sync word and its inverse.

// ARGOS 4 PTT-VLD-A4 A4-SS-TER-SP-0079-CNES defines a sync pattern of 0xAC5353
Expand Down