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direwolf/demod_9600.c
WB2OSZ 8978f2de6c Version 1.0 - Initial commit 
Changes to be committed:
	new file:   .gitattributes
	new file:   .gitignore
	new file:   APRStt-Implementation-Notes.pdf
	new file:   CHANGES.txt
	new file:   LICENSE-dire-wolf.txt
	new file:   LICENSE-other.txt
	new file:   Makefile.linux
	new file:   Makefile.win
	new file:   Quick-Start-Guide-Windows.pdf
	new file:   Raspberry-Pi-APRS.pdf
	new file:   User-Guide.pdf
	new file:   aclients.c
	new file:   aprs_tt.c
	new file:   aprs_tt.h
	new file:   atest.c
	new file:   audio.c
	new file:   audio.h
	new file:   audio_win.c
	new file:   ax25_pad.c
	new file:   ax25_pad.h
	new file:   beacon.c
	new file:   beacon.h
	new file:   config.c
	new file:   config.h
	new file:   decode_aprs.c
	new file:   decode_aprs.h
	new file:   dedupe.c
	new file:   dedupe.h
	new file:   demod.c
	new file:   demod.h
	new file:   demod_9600.c
	new file:   demod_9600.h
	new file:   demod_afsk.c
	new file:   demod_afsk.h
	new file:   digipeater.c
	new file:   digipeater.h
	new file:   direwolf.c
	new file:   direwolf.conf
	new file:   direwolf.desktop
	new file:   direwolf.h
	new file:   dsp.c
	new file:   dsp.h
	new file:   dtmf.c
	new file:   dtmf.h
	new file:   dw-icon.ico
	new file:   dw-icon.png
	new file:   dw-icon.rc
	new file:   dw-start.sh
	new file:   dwgps.c
	new file:   dwgps.h
	new file:   encode_aprs.c
	new file:   encode_aprs.h
	new file:   fcs_calc.c
	new file:   fcs_calc.h
	new file:   fsk_demod_agc.h
	new file:   fsk_demod_state.h
	new file:   fsk_filters.h
	new file:   fsk_gen_filter.h
	new file:   gen_packets.c
	new file:   gen_tone.c
	new file:   gen_tone.h
	new file:   hdlc_rec.c
	new file:   hdlc_rec.h
	new file:   hdlc_rec2.c
	new file:   hdlc_rec2.h
	new file:   hdlc_send.c
	new file:   hdlc_send.h
	new file:   igate.c
	new file:   igate.h
	new file:   kiss.c
	new file:   kiss.h
	new file:   kiss_frame.c
	new file:   kiss_frame.h
	new file:   kissnet.c
	new file:   kissnet.h
	new file:   latlong.c
	new file:   latlong.h
	new file:   ll2utm.c
	new file:   misc/README-dire-wolf.txt
	new file:   misc/strcasestr.c
	new file:   misc/strsep.c
	new file:   misc/strtok_r.c
	new file:   morse.c
	new file:   multi_modem.c
	new file:   multi_modem.h
	new file:   ptt.c
	new file:   ptt.h
	new file:   pttest.c
	new file:   rdq.c
	new file:   rdq.h
	new file:   redecode.c
	new file:   redecode.h
	new file:   regex/COPYING
	new file:   regex/INSTALL
	new file:   regex/LICENSES
	new file:   regex/NEWS
	new file:   regex/README
	new file:   regex/README-dire-wolf.txt
	new file:   regex/re_comp.h
	new file:   regex/regcomp.c
	new file:   regex/regex.c
	new file:   regex/regex.h
	new file:   regex/regex_internal.c
	new file:   regex/regex_internal.h
	new file:   regex/regexec.c
	new file:   rrbb.c
	new file:   rrbb.h
	new file:   server.c
	new file:   server.h
	new file:   symbols-new.txt
	new file:   symbols.c
	new file:   symbols.h
	new file:   symbolsX.txt
	new file:   textcolor.c
	new file:   textcolor.h
	new file:   tocalls.txt
	new file:   tq.c
	new file:   tq.h
	new file:   tt_text.c
	new file:   tt_text.h
	new file:   tt_user.c
	new file:   tt_user.h
	new file:   tune.h
	new file:   udp_test.c
	new file:   utm/LatLong-UTMconversion.c
	new file:   utm/LatLong-UTMconversion.h
	new file:   utm/README.txt
	new file:   utm/SwissGrid.cpp
	new file:   utm/UTMConversions.cpp
	new file:   utm/constants.h
	new file:   utm2ll.c
	new file:   version.h
	new file:   xmit.c
	new file:   xmit.h
2015-07-26 20:35:07 -04:00

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//
// This file is part of Dire Wolf, an amateur radio packet TNC.
//
// Copyright (C) 2011,2012,2013 John Langner, WB2OSZ
//
// This program is free software: you can redistribute it 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 program 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/>.
//
// #define DEBUG5 1 /* capture 9600 output to log files */
/*------------------------------------------------------------------
*
* Module: demod_9600.c
*
* Purpose: Demodulator for scrambled baseband encoding.
*
* Input: Audio samples from either a file or the "sound card."
*
* Outputs: Calls hdlc_rec_bit() for each bit demodulated.
*
*---------------------------------------------------------------*/
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <unistd.h>
#include <sys/stat.h>
#include <string.h>
#include <assert.h>
#include <ctype.h>
#include "direwolf.h"
#include "tune.h"
#include "fsk_demod_state.h"
#include "hdlc_rec.h"
#include "demod_9600.h"
#include "textcolor.h"
#include "dsp.h"
/* Add sample to buffer and shift the rest down. */
__attribute__((hot))
static inline void push_sample (float val, float *buff, int size)
{
int j;
// TODO: memmove any faster?
for (j = size - 1; j >= 1; j--) {
buff[j] = buff[j-1];
}
buff[0] = val;
}
/* FIR filter kernel. */
__attribute__((hot))
static inline float convolve (const float *data, const float *filter, int filter_size)
{
float sum = 0;
int j;
for (j=0; j<filter_size; j++) {
sum += filter[j] * data[j];
}
return (sum);
}
/* Automatic gain control. */
/* Result should settle down to 1 unit peak to peak. i.e. -0.5 to +0.5 */
__attribute__((hot))
static inline float agc (float in, float fast_attack, float slow_decay, float *ppeak, float *pvalley)
{
if (in >= *ppeak) {
*ppeak = in * fast_attack + *ppeak * (1. - fast_attack);
}
else {
*ppeak = in * slow_decay + *ppeak * (1. - slow_decay);
}
if (in <= *pvalley) {
*pvalley = in * fast_attack + *pvalley * (1. - fast_attack);
}
else {
*pvalley = in * slow_decay + *pvalley * (1. - slow_decay);
}
if (*ppeak > *pvalley) {
return ((in - 0.5 * (*ppeak + *pvalley)) / (*ppeak - *pvalley));
}
return (0.0);
}
/*------------------------------------------------------------------
*
* Name: demod_9600_init
*
* Purpose: Initialize the 9600 baud demodulator.
*
* Inputs: samples_per_sec - Number of samples per second.
* Might be upsampled in hopes of
* reducing the PLL jitter.
*
* baud - Data rate in bits per second.
*
* D - Address of demodulator state.
*
* Returns: None
*
*----------------------------------------------------------------*/
void demod_9600_init (int samples_per_sec, int baud, struct demodulator_state_s *D)
{
float fc;
memset (D, 0, sizeof(struct demodulator_state_s));
//dw_printf ("demod_9600_init(rate=%d, baud=%d, D ptr)\n", samples_per_sec, baud);
D->pll_step_per_sample =
(int) round(TICKS_PER_PLL_CYCLE * (double) baud / (double)samples_per_sec);
D->filter_len_bits = 72 * 9600.0 / (44100.0 * 2.0);
D->lp_filter_size = (int) (( D->filter_len_bits * (float)samples_per_sec / baud) + 0.5);
#if TUNE_LP_FILTER_SIZE
D->lp_filter_size = TUNE_LP_FILTER_SIZE;
#endif
D->lpf_baud = 0.59;
#ifdef TUNE_LPF_BAUD
D->lpf_baud = TUNE_LPF_BAUD;
#endif
D->agc_fast_attack = 0.080;
#ifdef TUNE_AGC_FAST
D->agc_fast_attack = TUNE_AGC_FAST;
#endif
D->agc_slow_decay = 0.00012;
#ifdef TUNE_AGC_SLOW
D->agc_slow_decay = TUNE_AGC_SLOW;
#endif
D->pll_locked_inertia = 0.88;
D->pll_searching_inertia = 0.67;
#if defined(TUNE_PLL_LOCKED) && defined(TUNE_PLL_SEARCHING)
D->pll_locked_inertia = TUNE_PLL_LOCKED;
D->pll_searching_inertia = TUNE_PLL_SEARCHING;
#endif
fc = (float)baud * D->lpf_baud / (float)samples_per_sec;
//dw_printf ("demod_9600_init: call gen_lowpass(fc=%.2f, , size=%d, )\n", fc, D->lp_filter_size);
gen_lowpass (fc, D->lp_filter, D->lp_filter_size, BP_WINDOW_HAMMING);
} /* end fsk_demod_init */
/*-------------------------------------------------------------------
*
* Name: demod_9600_process_sample
*
* Purpose: (1) Filter & slice the signal.
* (2) Descramble it.
* (2) Recover clock and data.
*
* Inputs: chan - Audio channel. 0 for left, 1 for right.
*
* sam - One sample of audio.
* Should be in range of -32768 .. 32767.
*
* Returns: None
*
* Descripion: "9600 baud" packet is FSK for an FM voice transceiver.
* By the time it gets here, it's really a baseband signal.
* At one extreme, we could have a 4800 Hz square wave.
* A the other extreme, we could go a considerable number
* of bit times without any transitions.
*
* The trick is to extract the digital data which has
* been distorted by going thru voice transceivers not
* intended to pass this sort of "audio" signal.
*
* Data is "scrambled" to reduce the amount of DC bias.
* The data stream must be unscrambled at the receiving end.
*
* We also have a digital phase locked loop (PLL)
* to recover the clock and pick out data bits at
* the proper rate.
*
* For each recovered data bit, we call:
*
* hdlc_rec (channel, demodulated_bit);
*
* to decode HDLC frames from the stream of bits.
*
* Future: This could be generalized by passing in the name
* of the function to be called for each bit recovered
* from the demodulator. For now, it's simply hard-coded.
*
* References: 9600 Baud Packet Radio Modem Design
* http://www.amsat.org/amsat/articles/g3ruh/109.html
*
* The KD2BD 9600 Baud Modem
* http://www.amsat.org/amsat/articles/kd2bd/9k6modem/
*
* 9600 Baud Packet Handbook
* ftp://ftp.tapr.org/general/9600baud/96man2x0.txt
*
*
* TODO: This works in a simulated environment but it has not yet
* been successfully tested for interoperability with
* other systems over the air.
* That's why it is not mentioned in documentation.
*
* The signal from the radio speaker does NOT have
* enough bandwidth and the waveform is hopelessly distorted.
* It will be necessary to obtain a signal right after
* the discriminator of the receiver.
* It will probably also be necessary to tap directly into
* the modulator, bypassing the microphone amplifier.
*
*--------------------------------------------------------------------*/
__attribute__((hot))
void demod_9600_process_sample (int chan, int sam, struct demodulator_state_s *D)
{
float fsam;
float abs_fsam;
float amp;
float demod_out;
#if DEBUG5
static FILE *demod_log_fp = NULL;
static int seq = 0; /* for log file name */
#endif
int j;
int subchan = 0;
int demod_data; /* Still scrambled. */
static int descram; /* Data bit de-scrambled. */
assert (chan >= 0 && chan < MAX_CHANS);
assert (subchan >= 0 && subchan < MAX_SUBCHANS);
/*
* Filters use last 'filter_size' samples.
*
* First push the older samples down.
*
* Finally, put the most recent at the beginning.
*
* Future project? Rather than shifting the samples,
* it might be faster to add another variable to keep
* track of the most recent sample and change the
* indexing in the later loops that multipy and add.
*/
/* Scale to nice number, range -1.0 to +1.0. */
fsam = sam / 32768.0;
push_sample (fsam, D->raw_cb, D->lp_filter_size);
/*
* Low pass filter to reduce noise yet pass the data.
*/
amp = convolve (D->raw_cb, D->lp_filter, D->lp_filter_size);
/*
* The input level can vary greatly.
* More importantly, there could be a DC bias which we need to remove.
*
* Normalize the signal with automatic gain control (AGC).
* This works by looking at the minimum and maximum signal peaks
* and scaling the results to be roughly in the -1.0 to +1.0 range.
*/
demod_out = 2.0 * agc (amp, D->agc_fast_attack, D->agc_slow_decay, &(D->m_peak), &(D->m_valley));
//dw_printf ("peak=%.2f valley=%.2f amp=%.2f norm=%.2f\n", D->m_peak, D->m_valley, amp, norm);
/* Throw in a little Hysteresis??? */
/* (Not to be confused with Hysteria.) */
if (demod_out > 0.01) {
demod_data = 1;
}
else if (demod_out < -0.01) {
demod_data = 0;
}
else {
demod_data = D->prev_demod_data;
}
/*
* Next, a PLL is used to sample near the centers of the data bits.
*
* D->data_clock_pll is a SIGNED 32 bit variable.
* When it overflows from a large positive value to a negative value, we
* sample a data bit from the demodulated signal.
*
* Ideally, the the demodulated signal transitions should be near
* zero we we sample mid way between the transitions.
*
* Nudge the PLL by removing some small fraction from the value of
* data_clock_pll, pushing it closer to zero.
*
* This adjustment will never change the sign so it won't cause
* any erratic data bit sampling.
*
* If we adjust it too quickly, the clock will have too much jitter.
* If we adjust it too slowly, it will take too long to lock on to a new signal.
*
* I don't think the optimal value will depend on the audio sample rate
* because this happens for each transition from the demodulator.
*
* This was optimized for 1200 baud AFSK. There might be some opportunity
* for improvement here.
*/
D->prev_d_c_pll = D->data_clock_pll;
D->data_clock_pll += D->pll_step_per_sample;
if (D->data_clock_pll < 0 && D->prev_d_c_pll > 0) {
/* Overflow. */
/*
* At this point, we need to descramble the data as
* in hardware based designs by G3RUH and K9NG.
*
* http://www.amsat.org/amsat/articles/g3ruh/109/fig03.gif
*/
//assert (modem.modem_type[chan] == SCRAMBLE);
//if (modem.modem_type[chan] == SCRAMBLE) {
// TODO: This needs to be rearranged to allow attempted "fixing"
// of corrupted bits later. We need to store the original
// received bits and do the descrambling after attempted
// repairs. However, we also need to descramble now to
// detect the flag sequences.
descram = descramble (demod_data, &(D->lfsr));
#if SLICENDICE
// TODO: Needs more thought.
// Does it even make sense to remember demod_out in this case?
// We would need to do the re-thresholding before descrambling.
//hdlc_rec_bit_sam (chan, subchan, descram, descram ? 1.0 : -1.0);
#else
// TODO: raw received bit and true later.
hdlc_rec_bit (chan, subchan, descram, 0, D->lfsr);
#endif
//D->prev_descram = descram;
//}
//else {
/* Baseband signal for completeness - not in common use. */
#if SLICENDICE
//hdlc_rec_bit_sam (chan, subchan, demod_data, demod_data ? 1.0 : -1.0);
#else
//hdlc_rec_bit (chan, subchan, demod_data);
#endif
//}
}
if (demod_data != D->prev_demod_data) {
// Note: Test for this demodulator, not overall for channel.
if (hdlc_rec_data_detect_1 (chan, subchan)) {
D->data_clock_pll = (int)(D->data_clock_pll * D->pll_locked_inertia);
}
else {
D->data_clock_pll = (int)(D->data_clock_pll * D->pll_searching_inertia);
}
}
#if DEBUG5
//if (chan == 0) {
if (hdlc_rec_data_detect_1 (chan,subchan)) {
char fname[30];
if (demod_log_fp == NULL) {
seq++;
sprintf (fname, "demod96/%04d.csv", seq);
if (seq == 1) mkdir ("demod96"
#ifndef __WIN32__
, 0777
#endif
);
demod_log_fp = fopen (fname, "w");
text_color_set(DW_COLOR_DEBUG);
dw_printf ("Starting 9600 decoder log file %s\n", fname);
fprintf (demod_log_fp, "Audio, Peak, Valley, Demod, SData, Descram, Clock\n");
}
fprintf (demod_log_fp, "%.3f, %.3f, %.3f, %.3f, %.2f, %.2f, %.2f\n",
0.5 * fsam + 3.5,
0.5 * D->m_peak + 3.5,
0.5 * D->m_valley + 3.5,
0.5 * demod_out + 2.0,
demod_data ? 1.35 : 1.0,
descram ? .9 : .55,
(D->data_clock_pll & 0x80000000) ? .1 : .45);
}
else {
if (demod_log_fp != NULL) {
fclose (demod_log_fp);
demod_log_fp = NULL;
}
}
//}
#endif
/*
* Remember demodulator output (pre-descrambling) so we can compare next time
* for the DPLL sync.
*/
D->prev_demod_data = demod_data;
} /* end demod_9600_process_sample */
/* end demod_9600.c */
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