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freeswitch/libs/spandsp/src/fsk.c

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/*
* SpanDSP - a series of DSP components for telephony
*
* fsk.c - FSK modem transmit and receive parts
*
* Written by Steve Underwood <steveu@coppice.org>
*
* Copyright (C) 2003 Steve Underwood
*
* All rights reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version 2.1,
* as published by the Free Software Foundation.
*
* 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 Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*! \file */
#if defined(HAVE_CONFIG_H)
#include "config.h"
#endif
#include <stdlib.h>
#include <inttypes.h>
#include <string.h>
#if defined(HAVE_TGMATH_H)
#include <tgmath.h>
#endif
#if defined(HAVE_MATH_H)
#include <math.h>
#endif
#include "floating_fudge.h"
#include <assert.h>
#include "spandsp/telephony.h"
#include "spandsp/complex.h"
#include "spandsp/dds.h"
#include "spandsp/power_meter.h"
#include "spandsp/async.h"
#include "spandsp/fsk.h"
#include "spandsp/private/fsk.h"
const fsk_spec_t preset_fsk_specs[] =
{
{
"V21 ch 1",
1080 + 100,
1080 - 100,
-14,
-30,
300*100
},
{
"V21 ch 2",
1750 + 100,
1750 - 100,
-14,
-30,
300*100
},
{
"V23 ch 1",
2100,
1300,
-14,
-30,
1200*100
},
{
"V23 ch 2",
450,
390,
-14,
-30,
75*100
},
{
"Bell103 ch 1",
2125 - 100,
2125 + 100,
-14,
-30,
300*100
},
{
"Bell103 ch 2",
1170 - 100,
1170 + 100,
-14,
-30,
300*100
},
{
"Bell202",
2200,
1200,
-14,
-30,
1200*100
},
{
"Weitbrecht 45.45", /* Used for TDD (Telecoms Device for the Deaf) */
1800,
1400,
-14,
-30,
4545
},
{
"Weitbrecht 50", /* Used for TDD (Telecoms Device for the Deaf) */
1800,
1400,
-14,
-30,
5000
}
};
SPAN_DECLARE(int) fsk_tx_restart(fsk_tx_state_t *s, const fsk_spec_t *spec)
{
s->baud_rate = spec->baud_rate;
s->phase_rates[0] = dds_phase_rate((float) spec->freq_zero);
s->phase_rates[1] = dds_phase_rate((float) spec->freq_one);
s->scaling = dds_scaling_dbm0((float) spec->tx_level);
/* Initialise fractional sample baud generation. */
s->phase_acc = 0;
s->baud_frac = 0;
s->current_phase_rate = s->phase_rates[1];
s->shutdown = FALSE;
return 0;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(fsk_tx_state_t *) fsk_tx_init(fsk_tx_state_t *s,
const fsk_spec_t *spec,
get_bit_func_t get_bit,
void *user_data)
{
if (s == NULL)
{
if ((s = (fsk_tx_state_t *) malloc(sizeof(*s))) == NULL)
return NULL;
}
memset(s, 0, sizeof(*s));
s->get_bit = get_bit;
s->get_bit_user_data = user_data;
fsk_tx_restart(s, spec);
return s;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(int) fsk_tx_release(fsk_tx_state_t *s)
{
return 0;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(int) fsk_tx_free(fsk_tx_state_t *s)
{
free(s);
return 0;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE_NONSTD(int) fsk_tx(fsk_tx_state_t *s, int16_t amp[], int len)
{
int sample;
int bit;
if (s->shutdown)
return 0;
/* Make the transitions between 0 and 1 phase coherent, but instantaneous
jumps. There is currently no interpolation for bauds that end mid-sample.
Mainstream users will not care. Some specialist users might have a problem
with them, if they care about accurate transition timing. */
for (sample = 0; sample < len; sample++)
{
if ((s->baud_frac += s->baud_rate) >= SAMPLE_RATE*100)
{
s->baud_frac -= SAMPLE_RATE*100;
if ((bit = s->get_bit(s->get_bit_user_data)) == SIG_STATUS_END_OF_DATA)
{
if (s->status_handler)
s->status_handler(s->status_user_data, SIG_STATUS_END_OF_DATA);
if (s->status_handler)
s->status_handler(s->status_user_data, SIG_STATUS_SHUTDOWN_COMPLETE);
s->shutdown = TRUE;
break;
}
s->current_phase_rate = s->phase_rates[bit & 1];
}
amp[sample] = dds_mod(&(s->phase_acc), s->current_phase_rate, s->scaling, 0);
}
return sample;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(void) fsk_tx_power(fsk_tx_state_t *s, float power)
{
s->scaling = dds_scaling_dbm0(power);
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(void) fsk_tx_set_get_bit(fsk_tx_state_t *s, get_bit_func_t get_bit, void *user_data)
{
s->get_bit = get_bit;
s->get_bit_user_data = user_data;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(void) fsk_tx_set_modem_status_handler(fsk_tx_state_t *s, modem_tx_status_func_t handler, void *user_data)
{
s->status_handler = handler;
s->status_user_data = user_data;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(void) fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff)
{
/* The 6.04 allows for the gain of the DC blocker */
s->carrier_on_power = (int32_t) (power_meter_level_dbm0(cutoff + 2.5f - 6.04f));
s->carrier_off_power = (int32_t) (power_meter_level_dbm0(cutoff - 2.5f - 6.04f));
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(float) fsk_rx_signal_power(fsk_rx_state_t *s)
{
return power_meter_current_dbm0(&s->power);
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(void) fsk_rx_set_put_bit(fsk_rx_state_t *s, put_bit_func_t put_bit, void *user_data)
{
s->put_bit = put_bit;
s->put_bit_user_data = user_data;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(void) fsk_rx_set_modem_status_handler(fsk_rx_state_t *s, modem_tx_status_func_t handler, void *user_data)
{
s->status_handler = handler;
s->status_user_data = user_data;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(int) fsk_rx_restart(fsk_rx_state_t *s, const fsk_spec_t *spec, int framing_mode)
{
int chop;
s->baud_rate = spec->baud_rate;
s->framing_mode = framing_mode;
fsk_rx_signal_cutoff(s, (float) spec->min_level);
/* Detect by correlating against the tones we want, over a period
of one baud. The correlation must be quadrature. */
/* First we need the quadrature tone generators to correlate
against. */
s->phase_rate[0] = dds_phase_rate((float) spec->freq_zero);
s->phase_rate[1] = dds_phase_rate((float) spec->freq_one);
s->phase_acc[0] = 0;
s->phase_acc[1] = 0;
s->last_sample = 0;
/* The correlation should be over one baud. */
s->correlation_span = SAMPLE_RATE*100/spec->baud_rate;
/* But limit it for very slow baud rates, so we do not overflow our
buffer. */
if (s->correlation_span > FSK_MAX_WINDOW_LEN)
s->correlation_span = FSK_MAX_WINDOW_LEN;
/* We need to scale, to avoid overflow in the correlation. */
s->scaling_shift = 0;
chop = s->correlation_span;
while (chop != 0)
{
s->scaling_shift++;
chop >>= 1;
}
/* Initialise the baud/bit rate tracking. */
s->baud_phase = 0;
s->frame_state = 0;
s->frame_bits = 0;
s->last_bit = 0;
/* Initialise a power detector, so sense when a signal is present. */
power_meter_init(&(s->power), 4);
s->signal_present = 0;
return 0;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(fsk_rx_state_t *) fsk_rx_init(fsk_rx_state_t *s,
const fsk_spec_t *spec,
int framing_mode,
put_bit_func_t put_bit,
void *user_data)
{
if (s == NULL)
{
if ((s = (fsk_rx_state_t *) malloc(sizeof(*s))) == NULL)
return NULL;
}
memset(s, 0, sizeof(*s));
s->put_bit = put_bit;
s->put_bit_user_data = user_data;
fsk_rx_restart(s, spec, framing_mode);
return s;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(int) fsk_rx_release(fsk_rx_state_t *s)
{
return 0;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE(int) fsk_rx_free(fsk_rx_state_t *s)
{
free(s);
return 0;
}
/*- End of function --------------------------------------------------------*/
static void report_status_change(fsk_rx_state_t *s, int status)
{
if (s->status_handler)
s->status_handler(s->status_user_data, status);
else if (s->put_bit)
s->put_bit(s->put_bit_user_data, status);
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE_NONSTD(int) fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len)
{
int buf_ptr;
int baudstate;
int i;
int j;
int16_t x;
int32_t dot;
int32_t sum[2];
int32_t power;
complexi_t ph;
buf_ptr = s->buf_ptr;
for (i = 0; i < len; i++)
{
/* The *totally* asynchronous character to character behaviour of these
modems, when carrying async. data, seems to force a sample by sample
approach. */
for (j = 0; j < 2; j++)
{
s->dot[j].re -= s->window[j][buf_ptr].re;
s->dot[j].im -= s->window[j][buf_ptr].im;
ph = dds_complexi(&(s->phase_acc[j]), s->phase_rate[j]);
s->window[j][buf_ptr].re = (ph.re*amp[i]) >> s->scaling_shift;
s->window[j][buf_ptr].im = (ph.im*amp[i]) >> s->scaling_shift;
s->dot[j].re += s->window[j][buf_ptr].re;
s->dot[j].im += s->window[j][buf_ptr].im;
dot = s->dot[j].re >> 15;
sum[j] = dot*dot;
dot = s->dot[j].im >> 15;
sum[j] += dot*dot;
}
/* If there isn't much signal, don't demodulate - it will only produce
useless junk results. */
/* There should be no DC in the signal, but sometimes there is.
We need to measure the power with the DC blocked, but not using
a slow to respond DC blocker. Use the most elementary HPF. */
x = amp[i] >> 1;
power = power_meter_update(&(s->power), x - s->last_sample);
s->last_sample = x;
if (s->signal_present)
{
/* Look for power below turn-off threshold to turn the carrier off */
if (power < s->carrier_off_power)
{
if (--s->signal_present <= 0)
{
/* Count down a short delay, to ensure we push the last
few bits through the filters before stopping. */
report_status_change(s, SIG_STATUS_CARRIER_DOWN);
s->baud_phase = 0;
continue;
}
}
}
else
{
/* Look for power exceeding turn-on threshold to turn the carrier on */
if (power < s->carrier_on_power)
{
s->baud_phase = 0;
continue;
}
if (s->baud_phase < (s->correlation_span >> 1) - 30)
{
s->baud_phase++;
continue;
}
s->signal_present = 1;
/* Initialise the baud/bit rate tracking. */
s->baud_phase = 0;
s->frame_state = 0;
s->frame_bits = 0;
s->last_bit = 0;
report_status_change(s, SIG_STATUS_CARRIER_UP);
}
/* Non-coherent FSK demodulation by correlation with the target tones
over a one baud interval. The slow V.xx specs. are too open ended
to allow anything fancier to be used. The dot products are calculated
using a sliding window approach, so the compute load is not that great. */
baudstate = (sum[0] < sum[1]);
switch (s->framing_mode)
{
case FSK_FRAME_MODE_SYNC:
/* Synchronous serial operation - e.g. for HDLC */
if (s->last_bit != baudstate)
{
/* On a transition we check our timing */
s->last_bit = baudstate;
/* For synchronous use (e.g. HDLC channels in FAX modems), nudge
the baud phase gently, trying to keep it centred on the bauds. */
if (s->baud_phase < (SAMPLE_RATE*50))
s->baud_phase += (s->baud_rate >> 3);
else
s->baud_phase -= (s->baud_rate >> 3);
}
if ((s->baud_phase += s->baud_rate) >= (SAMPLE_RATE*100))
{
/* We should be in the middle of a baud now, so report the current
state as the next bit */
s->baud_phase -= (SAMPLE_RATE*100);
s->put_bit(s->put_bit_user_data, baudstate);
}
break;
case FSK_FRAME_MODE_ASYNC:
/* Fully asynchronous mode */
if (s->last_bit != baudstate)
{
/* On a transition we check our timing */
s->last_bit = baudstate;
/* For async. operation, believe transitions completely, and
sample appropriately. This allows instant start on the first
transition. */
/* We must now be about half way to a sampling point. We do not do
any fractional sample estimation of the transitions, so this is
the most accurate baud alignment we can do. */
s->baud_phase = SAMPLE_RATE*50;
}
if ((s->baud_phase += s->baud_rate) >= (SAMPLE_RATE*100))
{
/* We should be in the middle of a baud now, so report the current
state as the next bit */
s->baud_phase -= (SAMPLE_RATE*100);
s->put_bit(s->put_bit_user_data, baudstate);
}
break;
default:
/* Gather the specified number of bits, with robust checking to ensure reasonable voice immunity.
The first bit should be a start bit (0), and the last bit should be a stop bit (1) */
if (s->frame_state == 0)
{
/* Looking for the start of a zero bit, which hopefully the start of a start bit */
if (baudstate == 0)
{
s->baud_phase = SAMPLE_RATE*(100 - 40)/2;
s->frame_state = -1;
s->frame_bits = 0;
s->last_bit = -1;
}
}
else if (s->frame_state == -1)
{
/* Look for a continuous zero from the start of the start bit until
beyond the middle */
if (baudstate != 0)
{
/* If we aren't looking at a stable start bit, restart */
s->frame_state = 0;
}
else
{
s->baud_phase += s->baud_rate;
if (s->baud_phase >= SAMPLE_RATE*100)
{
s->frame_state = 1;
s->last_bit = baudstate;
}
}
}
else
{
s->baud_phase += s->baud_rate;
if (s->baud_phase >= SAMPLE_RATE*(100 - 40))
{
if (s->last_bit < 0)
s->last_bit = baudstate;
/* Look for the bit being consistent over the central 20% of the bit time. */
if (s->last_bit != baudstate)
{
s->frame_state = 0;
}
else if (s->baud_phase >= SAMPLE_RATE*100)
{
/* We should be in the middle of a baud now, so report the current
state as the next bit */
if (s->last_bit == baudstate)
{
s->frame_bits |= (baudstate << s->framing_mode);
s->frame_bits >>= 1;
s->baud_phase -= (SAMPLE_RATE*100);
if (++s->frame_state > s->framing_mode)
{
/* Check we have a stop bit */
if (baudstate == 1)
{
/* Check we have a start bit */
if ((s->frame_bits & 1) == 0)
{
/* Drop the start bit, and pass the rest back */
s->frame_bits >>= 1;
s->put_bit(s->put_bit_user_data, s->frame_bits);
}
}
s->frame_state = 0;
}
}
else
{
s->frame_state = 0;
}
s->last_bit = -1;
}
}
}
break;
}
if (++buf_ptr >= s->correlation_span)
buf_ptr = 0;
}
s->buf_ptr = buf_ptr;
return 0;
}
/*- End of function --------------------------------------------------------*/
SPAN_DECLARE_NONSTD(int) fsk_rx_fillin(fsk_rx_state_t *s, int len)
{
/* The valid choice here is probably to do nothing. We don't change state
(i.e carrier on<->carrier off), and we'll just output less bits than we
should. */
/* TODO: Advance the symbol phase the appropriate amount */
return 0;
}
/*- End of function --------------------------------------------------------*/
/*- End of file ------------------------------------------------------------*/
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