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AFSK1200Demod.cs
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AFSK1200Demod.cs
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using System;
namespace ax25
{
public class AFSK1200Demodulator
{
public bool ConsoleOut = false;
private int sample_rate;
private float decay;
private float[] td_filter;
private float[] cd_filter;
private int rate_index;
private float samples_per_bit;
private float[] u1, x;
private float[] c0_real, c0_imag, c1_real, c1_imag;
private float[] diff;
private float previous_fdiff;
private int last_transition;
private int data, bitcount;
private float phase_inc_f0, phase_inc_f1;
private float phase_inc_symbol;
private Packet packet; // received packet
private PacketHandler handler = null;
private sbyte[] lastPacket = null;
private int packetsDecoded = 0;
private enum State
{
WAITING,
JUST_SEEN_FLAG,
DECODING
}
private State state = State.WAITING;
private int filter_index;
private int emphasis;
private bool interpolate = false;
private float interpolate_last;
private bool interpolate_original;
private volatile bool data_carrier = false;
public PacketHandler OnPacket
{
set
{
this.handler = value;
}
}
public int DecodeCount
{
get
{
return packetsDecoded;
}
}
public sbyte[] LastPacket
{
get
{
return lastPacket;
}
}
public AFSK1200Demodulator(int sample_rate, int filter_length, PacketHandler h)
{
this.Init(sample_rate, filter_length, 0, h);
}
public AFSK1200Demodulator(int sample_rate, int filter_length)
{
this.Init(sample_rate, filter_length, 0, null);
}
public AFSK1200Demodulator(int sample_rate, int filter_length, int emphasis)
{
this.Init(sample_rate, filter_length, emphasis, null);
}
public AFSK1200Demodulator(int sample_rate, int filter_length, int emphasis, PacketHandler h)
{
this.Init(sample_rate, filter_length, emphasis, h);
}
private void Init(int sample_rate, int filter_length, int emphasis, PacketHandler h)
{
this.sample_rate = sample_rate;
this.emphasis = emphasis;
this.handler = h;
this.decay = (float)(1.0 - Math.Exp(Math.Log(0.5) / (double)sample_rate));
if (ConsoleOut)
Console.WriteLine("decay = {0:e}", (double)decay);
if (this.sample_rate == 8000)
{
interpolate = true;
this.sample_rate = 16000;
};
this.samples_per_bit = (float)sample_rate / 1200.0f;
if (ConsoleOut)
Console.WriteLine("samples per bit = {0}", this.samples_per_bit);
for (rate_index = 0; rate_index < AFSK1200Filters.sample_rates.Length; rate_index++)
if (AFSK1200Filters.sample_rates[rate_index] == sample_rate)
break;
if (rate_index == AFSK1200Filters.sample_rates.Length)
throw new Exception("Sample rate " + sample_rate + " not supported");
float[][][] tdf;
switch (emphasis)
{
case 0:
tdf = AFSK1200Filters.time_domain_filter_none;
break;
case 6:
tdf = AFSK1200Filters.time_domain_filter_full;
break;
default:
if (ConsoleOut)
Console.WriteLine("Filter for de-emphasis of {0}dB is not availabe, using 6dB", emphasis);
tdf = AFSK1200Filters.time_domain_filter_full;
break;
};
for (filter_index = 0; filter_index < tdf.Length; filter_index++)
{
if (ConsoleOut)
Console.WriteLine("Available filter length {0}", tdf[filter_index][rate_index].Length);
if (filter_length == tdf[filter_index][rate_index].Length)
{
if (ConsoleOut)
Console.WriteLine("Using filter length {0}", filter_length);
break;
}
};
if (filter_index == tdf.Length)
{
filter_index = tdf.Length - 1;
if (ConsoleOut)
Console.WriteLine("Filter length {0} not supported, using length {1}", filter_length, tdf[filter_index][rate_index].Length);
}
td_filter = tdf[filter_index][rate_index];
cd_filter = AFSK1200Filters.corr_diff_filter[filter_index][rate_index];
x = new float[td_filter.Length];
u1 = new float[td_filter.Length];
c0_real = new float[(int)Math.Floor(samples_per_bit)];
c0_imag = new float[(int)Math.Floor(samples_per_bit)];
c1_real = new float[(int)Math.Floor(samples_per_bit)];
c1_imag = new float[(int)Math.Floor(samples_per_bit)];
diff = new float[cd_filter.Length];
phase_inc_f0 = (float)(2.0 * Math.PI * 1200.0 / sample_rate);
phase_inc_f1 = (float)(2.0 * Math.PI * 2200.0 / sample_rate);
phase_inc_symbol = (float)(2.0 * Math.PI * 1200.0 / sample_rate);
}
private bool dcd()
{
return data_carrier;
}
private float correlation(float[] x, float[] y, int j)
{
float c = (float)0.0;
for (int i = 0; i < x.Length; i++)
{
c += x[j] * y[j];
j--;
if (j == -1)
j = x.Length - 1;
};
return c;
}
private float sum(float[] x, int j)
{
float c = (float)0.0;
for (int i = 0; i < x.Length; i++)
{
c += x[j--];
if (j == -1)
j = x.Length - 1;
}
return c;
}
private int j_td; // time domain index
private int j_cd; // time domain index
private int j_corr; // correlation index
private float phase_f0, phase_f1;
private int t; // running sample counter
private int flag_count = 0;
private bool flag_separator_seen = false; // to process the single-bit separation period between flags
public void AddSamples(double[] s, int n)
{
float[] _s = new float[n];
for (int i = 0; i < n; i++)
_s[i] = (float)s[i];
AddSamples(_s, n);
}
public void AddSamples(float[] s, int n)
{
int i = 0;
while (i < n)
{
float sample;
if (interpolate)
{
if (interpolate_original)
{
sample = s[i];
interpolate_last = sample;
interpolate_original = false;
i++;
}
else
{
sample = 0.5f * (s[i] + interpolate_last);
interpolate_original = true;
};
}
else
{
sample = s[i];
i++;
};
//if (sample > vox_threshold || sample < -vox_threshold) {
// vox_countdown = sample_rate; // 1s lingering
// if (vox_state==false)
// System.err.println("vox activating");
// vox_state = true;
//}
//if (vox_countdown == 0) {
// if (vox_state==true)
// System.err.println("vox deactivating");
// vox_state = false;
// continue;
//} else vox_countdown--;
u1[j_td] = sample;
//u1[j_td]= s[i];
//u2[j] = Filter.filter(u1, j, Filter.BANDPASS_1150_1250_48000_39);
//x[j] = Filter.filter(u2, j, Filter.BANDPASS_2150_2250_48000_39);
//u2[j] = Filter.filter(u1, j, Filter.BANDPASS_1150_1250_48000_39);
x[j_td] = Filter.filter(u1, j_td, td_filter);
// compute correlation running value
//c0_real[j] = x[j_td]*f0_cos[j];
//c0_imag[j] = x[j_td]*f0_sin[j];
//
//c1_real[j] = x[j_td]*f1_cos[j_f1];
//c1_imag[j] = x[j_td]*f1_sin[j_f1];
c0_real[j_corr] = x[j_td] * (float)Math.Cos(phase_f0);
c0_imag[j_corr] = x[j_td] * (float)Math.Sin(phase_f0);
c1_real[j_corr] = x[j_td] * (float)Math.Cos(phase_f1);
c1_imag[j_corr] = x[j_td] * (float)Math.Sin(phase_f1);
phase_f0 += phase_inc_f0;
if (phase_f0 > (float)(2.0 * Math.PI))
phase_f0 -= (float)(2.0 * Math.PI);
phase_f1 += phase_inc_f1;
if (phase_f1 > (float)(2.0 * Math.PI))
phase_f1 -= (float)(2.0 * Math.PI);
float cr = sum(c0_real, j_corr);
float ci = sum(c0_imag, j_corr);
float c0 = (float)Math.Sqrt(cr * cr + ci * ci);
cr = sum(c1_real, j_corr);
ci = sum(c1_imag, j_corr);
float c1 = (float)Math.Sqrt(cr * cr + ci * ci);
//diff[j_corr] = c0-c1;
diff[j_cd] = c0 - c1;
//fdiff[j_corr] = Filter.filter(diff,j_corr,Filter.LOWPASS_1200_48000_39);
//float fdiff = Filter.filter(diff,j_corr,cd_filter);
float fdiff = Filter.filter(diff, j_cd, cd_filter);
//System.out.printf("%d %f %f : ",j,diff[j],fdiff[j]);
//System.out.printf("%d %f %f %f %f : ",j,f0_cos[j],f0_sin[j],f1_cos[j_f1],f1_sin[j_f1]);
//float previous_fdiff = (j_corr==0) ? fdiff[fdiff.length-1] : fdiff[j_corr-1];
//if (previous_fdiff*fdiff[j_corr] < 0 || previous_fdiff==0) {
if (previous_fdiff * fdiff < 0 || previous_fdiff == 0)
{
// we found a transition
int p = t - last_transition;
last_transition = t;
int bits = (int)Math.Round((double)p / (double)samples_per_bit);
//System.out.printf("$ %f %d\n",(double) p / (double)samples_per_bit,bits);
if (bits == 0 || bits > 7)
{
state = State.WAITING;
data_carrier = false;
flag_count = 0;
}
else
{
if (bits == 7)
{
flag_count++;
flag_separator_seen = false;
//System.out.printf("Seen %d flags in a row\n",flag_count);
data = 0;
bitcount = 0;
switch (state)
{
case State.WAITING:
state = State.JUST_SEEN_FLAG;
data_carrier = true;
break;
case State.JUST_SEEN_FLAG:
break;
case State.DECODING:
if (packet != null && packet.terminate())
{
packetsDecoded++;
lastPacket = packet.bytesWithoutCRC();
if (handler != null)
handler.handlePacket(packet.bytesWithoutCRC());
};
packet = null;
state = State.JUST_SEEN_FLAG;
break;
};
}
else
{
switch (state)
{
case State.WAITING:
break;
case State.JUST_SEEN_FLAG:
state = State.DECODING;
break;
case State.DECODING:
break;
};
if (state == State.DECODING)
{
if (bits != 1)
flag_count = 0;
else
{
if (flag_count > 0 && !flag_separator_seen)
flag_separator_seen = true;
else
flag_count = 0;
};
for (int k = 0; k < bits - 1; k++)
{
bitcount++;
data >>= 1;
data += 128;
if (bitcount == 8)
{
if (packet == null)
packet = new Packet();
//if (data==0xAA) packet.terminate();
if (!packet.addByte((sbyte)data))
{
state = State.WAITING;
data_carrier = false;
};
//System.out.printf(">>> %02x %c %c\n", data, (char)data, (char)(data>>1));
data = 0;
bitcount = 0;
};
};
if (bits - 1 != 5) // the zero after the ones is not a stuffing
{
bitcount++;
data >>= 1;
if (bitcount == 8)
{
if (packet == null)
packet = new Packet();
//if (data==0xAA) packet.terminate();
if (!packet.addByte((sbyte)data))
{
state = State.WAITING;
data_carrier = false;
};
//System.out.printf(">>> %02x %c %c\n", data, (char)data, (char)(data>>1));
data = 0;
bitcount = 0;
};
};
};
};
};
};
previous_fdiff = fdiff;
t++;
j_td++;
if (j_td == td_filter.Length)
j_td = 0;
j_cd++;
if (j_cd == cd_filter.Length)
j_cd = 0;
j_corr++;
if (j_corr == c0_real.Length) // samples_per_bit
j_corr = 0;
//j++;
//if (j==samples_per_bit) j=0;
//j_f1++;
//if (j_f1==6*samples_per_bit) j_f1=0;
}
}
}
}