--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/fsk.c	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,358 @@
+/*
+ * 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 General Public License version 2, 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id: fsk.c,v 1.27 2006/11/19 14:07:24 steveu Exp $
+ */
+
+/*! \file */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <inttypes.h>
+#include <stdlib.h>
+#include <string.h>
+#if defined(HAVE_TGMATH_H)
+#include <tgmath.h>
+#endif
+#if defined(HAVE_MATH_H)
+#include <math.h>
+#endif
+#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"
+
+fsk_spec_t preset_fsk_specs[] =
+{
+    {
+        "V21 ch 1",
+        1080 + 100,
+        1080 - 100,
+        -14,
+        -30,
+        300
+    },
+    {
+        "V21 ch 2",
+        1750 + 100,
+        1750 - 100,
+        -14,
+        -30,
+        300
+    },
+    {
+        "V23 ch 1",
+        2100,
+        1300,
+        -14,
+        -30,
+        1200
+    },
+    {
+        "V23 ch 2",
+        450,
+        390,
+        -14,
+        -30,
+        75
+    },
+    {
+        "Bell103 ch 1",
+        2125 - 100,
+        2125 + 100,
+        -14,
+        -30,
+        300
+    },
+    {
+        "Bell103 ch 2",
+        1170 - 100,
+        1170 + 100,
+        -14,
+        -30,
+        300
+    },
+    {
+        "Bell202",
+        2200,
+        1200,
+        -14,
+        -30,
+        1200
+    },
+    {
+        "Weitbrecht",   /* Used for TDD (Telecomc Device for the Deaf) */
+        1800,
+        1400,
+        -14,
+        -30,
+         45             /* Actually 45.45 */
+    }
+};
+
+fsk_tx_state_t *fsk_tx_init(fsk_tx_state_t *s,
+                            fsk_spec_t *spec,
+                            get_bit_func_t get_bit,
+                            void *user_data)
+{
+    s->baud_rate = spec->baud_rate;
+    s->get_bit = get_bit;
+    s->user_data = user_data;
+
+    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_inc = (s->baud_rate*0x10000)/SAMPLE_RATE;
+    s->baud_frac = 0;
+    s->current_phase_rate = s->phase_rates[1];
+    
+    s->shutdown = FALSE;
+    return s;
+}
+/*- End of function --------------------------------------------------------*/
+
+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 they, if they care about accurate transition timing. */
+    for (sample = 0;  sample < len;  sample++)
+    {
+        if ((s->baud_frac += s->baud_inc) >= 0x10000)
+        {
+            s->baud_frac -= 0x10000;
+            if ((bit = s->get_bit(s->user_data)) == PUTBIT_END_OF_DATA)
+            {
+                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 --------------------------------------------------------*/
+
+void fsk_tx_power(fsk_tx_state_t *s, float power)
+{
+    s->scaling = dds_scaling_dbm0(power);
+}
+/*- End of function --------------------------------------------------------*/
+
+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->user_data = user_data;
+}
+/*- End of function --------------------------------------------------------*/
+
+void fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff)
+{
+    s->min_power = power_meter_level_dbm0(cutoff);
+}
+/*- End of function --------------------------------------------------------*/
+
+float fsk_rx_signal_power(fsk_rx_state_t *s)
+{
+    return power_meter_dbm0(&s->power);
+}
+/*- End of function --------------------------------------------------------*/
+
+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->user_data = user_data;
+}
+/*- End of function --------------------------------------------------------*/
+
+fsk_rx_state_t *fsk_rx_init(fsk_rx_state_t *s,
+                            fsk_spec_t *spec,
+                            int sync_mode,
+                            put_bit_func_t put_bit,
+                            void *user_data)
+{
+    int chop;
+
+    memset(s, 0, sizeof(*s));
+    s->baud_rate = spec->baud_rate;
+    s->sync_mode = sync_mode;
+    s->min_power = power_meter_level_dbm0((float) spec->min_level);
+    s->put_bit = put_bit;
+    s->user_data = user_data;
+
+    /* 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/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_inc = (s->baud_rate*0x10000)/SAMPLE_RATE;
+    s->baud_pll = 0;
+    
+    /* Initialise a power detector, so sense when a signal is present. */
+    power_meter_init(&(s->power), 4);
+    s->carrier_present = FALSE;
+    return s;
+}
+/*- End of function --------------------------------------------------------*/
+
+int fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len)
+{
+    int buf_ptr;
+    int baudstate;
+    int sample;
+    int j;
+    int32_t dot;
+    int32_t sum;
+    int32_t power;
+    icomplex_t ph;
+
+    buf_ptr = s->buf_ptr;
+
+    for (sample = 0;  sample < len;  sample++)
+    {
+        /* If there isn't much signal, don't demodulate - it will only produce
+           useless junk results. */
+        /* TODO: The carrier signal has no hysteresis! */
+        power = power_meter_update(&(s->power), amp[sample] - s->last_sample);
+        s->last_sample = amp[sample];
+        if (power < s->min_power)
+        {
+            if (s->carrier_present)
+            {
+                s->put_bit(s->user_data, PUTBIT_CARRIER_DOWN);
+                s->carrier_present = FALSE;
+            }
+            continue;
+        }
+        if (!s->carrier_present)
+        {
+            s->put_bit(s->user_data, PUTBIT_CARRIER_UP);
+            s->carrier_present = TRUE;
+        }
+        /* 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. */
+        /* 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_i[j] -= s->window_i[j][buf_ptr];
+            s->dot_q[j] -= s->window_q[j][buf_ptr];
+
+            ph = dds_complex(&(s->phase_acc[j]), s->phase_rate[j]);
+            s->window_i[j][buf_ptr] = (ph.re*amp[sample]) >> s->scaling_shift;
+            s->window_q[j][buf_ptr] = (ph.im*amp[sample]) >> s->scaling_shift;
+
+            s->dot_i[j] += s->window_i[j][buf_ptr];
+            s->dot_q[j] += s->window_q[j][buf_ptr];
+        }
+        dot = s->dot_i[0] >> 15;
+        sum = dot*dot;
+        dot = s->dot_q[0] >> 15;
+        sum += dot*dot;
+        dot = s->dot_i[1] >> 15;
+        sum -= dot*dot;
+        dot = s->dot_q[1] >> 15;
+        sum -= dot*dot;
+        baudstate = (sum < 0);
+
+        if (s->lastbit != baudstate)
+        {
+            s->lastbit = baudstate;
+            if (s->sync_mode)
+            {
+                /* 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_pll < 0x8000)
+                    s->baud_pll += (s->baud_inc >> 3);
+                else
+                    s->baud_pll -= (s->baud_inc >> 3);
+            }
+            else
+            {
+                /* 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_pll = 0x8000;
+            }
+
+        }
+        if ((s->baud_pll += s->baud_inc) >= 0x10000)
+        {
+            /* We should be in the middle of a baud now, so report the current
+               state as the next bit */
+            s->baud_pll -= 0x10000;
+            s->put_bit(s->user_data, baudstate);
+        }
+        if (++buf_ptr >= s->correlation_span)
+            buf_ptr = 0;
+    }
+    s->buf_ptr = buf_ptr;
+    return 0;
+}
+/*- End of function --------------------------------------------------------*/
+/*- End of file ------------------------------------------------------------*/