--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/bell_r2_mf.c	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,799 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * bell_r2_mf.c - Bell MF and MFC/R2 tone generation and detection.
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2001 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: bell_r2_mf.c,v 1.9 2006/11/19 14:07:24 steveu Exp $
+ */
+
+/*! \file bell_r2_mf.h */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <inttypes.h>
+#include <string.h>
+#include <time.h>
+#include <fcntl.h>
+#if defined(HAVE_TGMATH_H)
+#include <tgmath.h>
+#endif
+#if defined(HAVE_MATH_H)
+#include <math.h>
+#endif
+
+#include "spandsp/telephony.h"
+#include "spandsp/dc_restore.h"
+#include "spandsp/dds.h"
+#include "spandsp/tone_detect.h"
+#include "spandsp/tone_generate.h"
+#include "spandsp/bell_r2_mf.h"
+
+#if !defined(M_PI)
+/* C99 systems may not define M_PI */
+#define M_PI 3.14159265358979323846264338327
+#endif
+
+#define ms_to_samples(t)            (((t)*SAMPLE_RATE)/1000)
+
+typedef struct
+{
+    float       f1;         /* First freq */
+    float       f2;         /* Second freq */
+    int8_t      level1;     /* Level of the first freq (dB) */
+    int8_t      level2;     /* Level of the second freq (dB) */
+    uint8_t     on_time;    /* Tone on time (ms) */
+    uint8_t     off_time;   /* Minimum post tone silence (ms) */
+} mf_digit_tones_t;
+
+int bell_mf_gen_inited = FALSE;
+tone_gen_descriptor_t bell_mf_digit_tones[15];
+
+int r2_mf_gen_inited = FALSE;
+tone_gen_descriptor_t r2_mf_fwd_digit_tones[15];
+tone_gen_descriptor_t r2_mf_back_digit_tones[15];
+
+#if 0
+tone_gen_descriptor_t socotel_mf_digit_tones[18];
+#endif
+
+/* Bell R1 tone generation specs.
+ *  Power: -7dBm +- 1dB
+ *  Frequency: within +-1.5%
+ *  Mismatch between the start time of a pair of tones: <=6ms.
+ *  Mismatch between the end time of a pair of tones: <=6ms.
+ *  Tone duration: 68+-7ms, except KP which is 100+-7ms.
+ *  Inter-tone gap: 68+-7ms.
+ */
+static const mf_digit_tones_t bell_mf_tones[] =
+{
+    { 700.0f,  900.0f, -7, -7,  68, 68},
+    { 700.0f, 1100.0f, -7, -7,  68, 68},
+    { 900.0f, 1100.0f, -7, -7,  68, 68},
+    { 700.0f, 1300.0f, -7, -7,  68, 68},
+    { 900.0f, 1300.0f, -7, -7,  68, 68},
+    {1100.0f, 1300.0f, -7, -7,  68, 68},
+    { 700.0f, 1500.0f, -7, -7,  68, 68},
+    { 900.0f, 1500.0f, -7, -7,  68, 68},
+    {1100.0f, 1500.0f, -7, -7,  68, 68},
+    {1300.0f, 1500.0f, -7, -7,  68, 68},
+    { 700.0f, 1700.0f, -7, -7,  68, 68}, /* ST''' - use 'C' */
+    { 900.0f, 1700.0f, -7, -7,  68, 68}, /* ST'   - use 'A' */
+    {1100.0f, 1700.0f, -7, -7, 100, 68}, /* KP    - use '*' */
+    {1300.0f, 1700.0f, -7, -7,  68, 68}, /* ST''  - use 'B' */
+    {1500.0f, 1700.0f, -7, -7,  68, 68}, /* ST    - use '#' */
+    {0.0f, 0.0f, 0, 0, 0, 0}
+};
+
+/* The order of the digits here must match the list above */
+static const char bell_mf_tone_codes[] = "1234567890CA*B#";
+
+/* R2 tone generation specs.
+ *  Power: -11.5dBm +- 1dB
+ *  Frequency: within +-4Hz
+ *  Mismatch between the start time of a pair of tones: <=1ms.
+ *  Mismatch between the end time of a pair of tones: <=1ms.
+ */
+static const mf_digit_tones_t r2_mf_fwd_tones[] =
+{
+    {1380.0f, 1500.0f, -11, -11, 1, 0},
+    {1380.0f, 1620.0f, -11, -11, 1, 0},
+    {1500.0f, 1620.0f, -11, -11, 1, 0},
+    {1380.0f, 1740.0f, -11, -11, 1, 0},
+    {1500.0f, 1740.0f, -11, -11, 1, 0},
+    {1620.0f, 1740.0f, -11, -11, 1, 0},
+    {1380.0f, 1860.0f, -11, -11, 1, 0},
+    {1500.0f, 1860.0f, -11, -11, 1, 0},
+    {1620.0f, 1860.0f, -11, -11, 1, 0},
+    {1740.0f, 1860.0f, -11, -11, 1, 0},
+    {1380.0f, 1980.0f, -11, -11, 1, 0},
+    {1500.0f, 1980.0f, -11, -11, 1, 0},
+    {1620.0f, 1980.0f, -11, -11, 1, 0},
+    {1740.0f, 1980.0f, -11, -11, 1, 0},
+    {1860.0f, 1980.0f, -11, -11, 1, 0},
+    {0.0f, 0.0f, 0, 0, 0, 0}
+};
+
+static const mf_digit_tones_t r2_mf_back_tones[] =
+{
+    {1140.0f, 1020.0f, -11, -11, 1, 0},
+    {1140.0f,  900.0f, -11, -11, 1, 0},
+    {1020.0f,  900.0f, -11, -11, 1, 0},
+    {1140.0f,  780.0f, -11, -11, 1, 0},
+    {1020.0f,  780.0f, -11, -11, 1, 0},
+    { 900.0f,  780.0f, -11, -11, 1, 0},
+    {1140.0f,  660.0f, -11, -11, 1, 0},
+    {1020.0f,  660.0f, -11, -11, 1, 0},
+    { 900.0f,  660.0f, -11, -11, 1, 0},
+    { 780.0f,  660.0f, -11, -11, 1, 0},
+    {1140.0f,  540.0f, -11, -11, 1, 0},
+    {1020.0f,  540.0f, -11, -11, 1, 0},
+    { 900.0f,  540.0f, -11, -11, 1, 0},
+    { 780.0f,  540.0f, -11, -11, 1, 0},
+    { 660.0f,  540.0f, -11, -11, 1, 0},
+    {0.0f, 0.0f, 0, 0, 0, 0}
+};
+
+/* The order of the digits here must match the lists above */
+static const char r2_mf_tone_codes[] = "1234567890BCDEF";
+
+#if 0
+static const mf_digit_tones_t socotel_tones[] =
+{
+    { 700.0f,  900.0f, -11, -11, 1, 0},
+    { 700.0f, 1100.0f, -11, -11, 1, 0},
+    { 900.0f, 1100.0f, -11, -11, 1, 0},
+    { 700.0f, 1300.0f, -11, -11, 1, 0},
+    { 900.0f, 1300.0f, -11, -11, 1, 0},
+    {1100.0f, 1300.0f, -11, -11, 1, 0},
+    { 700.0f, 1500.0f, -11, -11, 1, 0},
+    { 900.0f, 1500.0f, -11, -11, 1, 0},
+    {1100.0f, 1500.0f, -11, -11, 1, 0},
+    {1300.0f, 1500.0f, -11, -11, 1, 0},
+    {1500.0f, 1700.0f, -11, -11, 1, 0},
+    { 700.0f, 1700.0f, -11, -11, 1, 0},
+    { 900.0f, 1700.0f, -11, -11, 1, 0},
+    {1300.0f, 1700.0f, -11, -11, 1, 0},
+    {1100.0f, 1700.0f, -11, -11, 1, 0},
+    {1700.0f,    0.0f, -11, -11, 1, 0},   /* Use 'F' */
+    {1900.0f,    0.0f, -11, -11, 1, 0},   /* Use 'G' */
+    {0.0f, 0.0f, 0, 0, 0, 0}
+};
+
+/* The order of the digits here must match the list above */
+static char socotel_mf_tone_codes[] = "1234567890ABCDEFG";
+#endif
+
+#define BELL_MF_THRESHOLD           1.6e9f
+#define BELL_MF_TWIST               4.0f    /* 6dB */
+#define BELL_MF_RELATIVE_PEAK       12.6f   /* 11dB */
+
+#define R2_MF_THRESHOLD             5.0e8f
+#define R2_MF_TWIST                 5.0f    /* 7dB */
+#define R2_MF_RELATIVE_PEAK         12.6f   /* 11dB */
+
+static goertzel_descriptor_t bell_mf_detect_desc[6];
+
+static goertzel_descriptor_t mf_fwd_detect_desc[6];
+static goertzel_descriptor_t mf_back_detect_desc[6];
+
+static const float bell_mf_frequencies[] =
+{
+     700.0f,  900.0f, 1100.0f, 1300.0f, 1500.0f, 1700.0f
+};
+
+/* Use the follow characters for the Bell MF special signals:
+    KP    - use '*'
+    ST    - use '#'
+    ST'   - use 'A'
+    ST''  - use 'B'
+    ST''' - use 'C' */
+static const char bell_mf_positions[] = "1247C-358A--69*---0B----#";
+
+static const float r2_mf_fwd_frequencies[] =
+{
+    1380.0f, 1500.0f, 1620.0f, 1740.0f, 1860.0f, 1980.0f
+};
+
+static const float r2_mf_back_frequencies[] =
+{
+    1140.0f, 1020.0f,  900.0f,  780.0f,  660.0f,  540.0f
+};
+
+/* Use codes '1' to 'F' for the R2 signals 1 to 15, except for signal 'A'.
+   Use '0' for this, so the codes match the digits 0-9. */
+static const char r2_mf_positions[] = "1247B-358C--69D---0E----F";
+
+static void bell_mf_gen_init(void)
+{
+    int i;
+    const mf_digit_tones_t *tones;
+
+    if (bell_mf_gen_inited)
+        return;
+    i = 0;
+    tones = bell_mf_tones;
+    while (tones->on_time)
+    {
+        /* Note: The duration of KP is longer than the other signals. */
+        make_tone_gen_descriptor(&bell_mf_digit_tones[i++],
+                                 (int) tones->f1,
+                                 tones->level1,
+                                 (int) tones->f2,
+                                 tones->level2,
+                                 tones->on_time,
+                                 tones->off_time,
+                                 0,
+                                 0,
+                                 FALSE);
+        tones++;
+    }
+    bell_mf_gen_inited = TRUE;
+}
+/*- End of function --------------------------------------------------------*/
+
+int bell_mf_tx(bell_mf_tx_state_t *s, int16_t amp[], int max_samples)
+{
+    int len;
+    size_t dig;
+    char *cp;
+
+    len = 0;
+    if (s->tones.current_section >= 0)
+    {
+        /* Deal with the fragment left over from last time */
+        len = tone_gen(&(s->tones), amp, max_samples);
+    }
+    dig = 0;
+    while (dig < s->current_digits  &&  len < max_samples)
+    {
+        /* Step to the next digit */
+        if ((cp = strchr(bell_mf_tone_codes, s->digits[dig++])) == NULL)
+            continue;
+        tone_gen_init(&(s->tones), &(s->tone_descriptors[cp - bell_mf_tone_codes]));
+        len += tone_gen(&(s->tones), amp + len, max_samples - len);
+    }
+    if (dig)
+    {
+        /* Shift out the consumed digits */
+        s->current_digits -= dig;
+        memmove(s->digits, s->digits + dig, s->current_digits);
+    }
+    return len;
+}
+/*- End of function --------------------------------------------------------*/
+
+size_t bell_mf_tx_put(bell_mf_tx_state_t *s, const char *digits)
+{
+    size_t len;
+
+    /* This returns the number of characters that would not fit in the buffer.
+       The buffer will only be loaded if the whole string of digits will fit,
+       in which case zero is returned. */
+    if ((len = strlen(digits)) > 0)
+    {
+        if (s->current_digits + len <= MAX_BELL_MF_DIGITS)
+        {
+            memcpy(s->digits + s->current_digits, digits, len);
+            s->current_digits += len;
+            len = 0;
+        }
+        else
+        {
+            len = MAX_BELL_MF_DIGITS - s->current_digits;
+        }
+    }
+    return len;
+}
+/*- End of function --------------------------------------------------------*/
+
+bell_mf_tx_state_t *bell_mf_tx_init(bell_mf_tx_state_t *s)
+{
+    if (!bell_mf_gen_inited)
+        bell_mf_gen_init();
+    s->tone_descriptors = bell_mf_digit_tones;
+    tone_gen_init(&(s->tones), &bell_mf_digit_tones[0]);
+    s->current_sample = 0;
+    s->current_digits = 0;
+    s->tones.current_section = -1;
+    return s;
+}
+/*- End of function --------------------------------------------------------*/
+
+int r2_mf_tx(r2_mf_tx_state_t *s, int16_t amp[], int samples, int fwd, char digit)
+{
+    int len;
+    char *cp;
+
+    len = 0;
+    if ((digit & 0x80))
+    {
+        /* Continue generating the tone we started earlier. */
+        len = tone_gen(&s->tone, amp, samples);
+    }
+    else if (digit == 0)
+    {
+        len = samples;
+        memset(amp, 0, len*sizeof(int16_t));
+    }
+    else
+    {
+        if ((cp = strchr(r2_mf_tone_codes, digit)))
+        {
+            if (fwd)
+                tone_gen_init(&s->tone, &r2_mf_fwd_digit_tones[cp - r2_mf_tone_codes]);
+            else
+                tone_gen_init(&s->tone, &r2_mf_back_digit_tones[cp - r2_mf_tone_codes]);
+            len = tone_gen(&s->tone, amp, samples);
+        }
+        else
+        {
+            len = samples;
+            memset(amp, 0, len*sizeof(int16_t));
+            
+        }
+    }
+    return len;
+}
+/*- End of function --------------------------------------------------------*/
+
+r2_mf_tx_state_t *r2_mf_tx_init(r2_mf_tx_state_t *s)
+{
+    int i;
+    const mf_digit_tones_t *tones;
+
+    if (!r2_mf_gen_inited)
+    {
+        i = 0;
+        tones = r2_mf_fwd_tones;
+        while (tones->on_time)
+        {
+            make_tone_gen_descriptor(&r2_mf_fwd_digit_tones[i++],
+                                     (int) tones->f1,
+                                     tones->level1,
+                                     (int) tones->f2,
+                                     tones->level2,
+                                     tones->on_time,
+                                     tones->off_time,
+                                     0,
+                                     0,
+                                     (tones->off_time == 0));
+            tones++;
+        }
+        i = 0;
+        tones = r2_mf_back_tones;
+        while (tones->on_time)
+        {
+            make_tone_gen_descriptor(&r2_mf_back_digit_tones[i++],
+                                     (int) tones->f1,
+                                     tones->level1,
+                                     (int) tones->f2,
+                                     tones->level2,
+                                     tones->on_time,
+                                     tones->off_time,
+                                     0,
+                                     0,
+                                     (tones->off_time == 0));
+            tones++;
+        }
+        r2_mf_gen_inited = TRUE;
+    }
+    memset(s, 0, sizeof(*s));
+    return s;
+}
+/*- End of function --------------------------------------------------------*/
+
+int bell_mf_rx(bell_mf_rx_state_t *s, const int16_t amp[], int samples)
+{
+    float energy[6];
+    float famp;
+    float v1;
+    int i;
+    int j;
+    int sample;
+    int best;
+    int second_best;
+    int limit;
+    uint8_t hit;
+
+    hit = 0;
+    for (sample = 0;  sample < samples;  sample = limit)
+    {
+        if ((samples - sample) >= (120 - s->current_sample))
+            limit = sample + (120 - s->current_sample);
+        else
+            limit = samples;
+        for (j = sample;  j < limit;  j++)
+        {
+            famp = amp[j];
+    
+            /* With GCC 2.95, the following unrolled code seems to take about 35%
+               (rough estimate) as long as a neat little 0-5 loop */
+            v1 = s->out[0].v2;
+            s->out[0].v2 = s->out[0].v3;
+            s->out[0].v3 = s->out[0].fac*s->out[0].v2 - v1 + famp;
+    
+            v1 = s->out[1].v2;
+            s->out[1].v2 = s->out[1].v3;
+            s->out[1].v3 = s->out[1].fac*s->out[1].v2 - v1 + famp;
+    
+            v1 = s->out[2].v2;
+            s->out[2].v2 = s->out[2].v3;
+            s->out[2].v3 = s->out[2].fac*s->out[2].v2 - v1 + famp;
+    
+            v1 = s->out[3].v2;
+            s->out[3].v2 = s->out[3].v3;
+            s->out[3].v3 = s->out[3].fac*s->out[3].v2 - v1 + famp;
+    
+            v1 = s->out[4].v2;
+            s->out[4].v2 = s->out[4].v3;
+            s->out[4].v3 = s->out[4].fac*s->out[4].v2 - v1 + famp;
+    
+            v1 = s->out[5].v2;
+            s->out[5].v2 = s->out[5].v3;
+            s->out[5].v3 = s->out[5].fac*s->out[5].v2 - v1 + famp;
+        }
+        s->current_sample += (limit - sample);
+        if (s->current_sample < 120)
+            continue;
+
+        /* We are at the end of an MF detection block */
+        /* Find the two highest energies. The spec says to look for
+           two tones and two tones only. Taking this literally -ie
+           only two tones pass the minimum threshold - doesn't work
+           well. The sinc function mess, due to rectangular windowing
+           ensure that! Find the two highest energies and ensure they
+           are considerably stronger than any of the others. */
+        energy[0] = goertzel_result(&s->out[0]);
+        energy[1] = goertzel_result(&s->out[1]);
+        if (energy[0] > energy[1])
+        {
+            best = 0;
+            second_best = 1;
+        }
+        else
+        {
+            best = 1;
+            second_best = 0;
+        }
+        for (i = 2;  i < 6;  i++)
+        {
+            energy[i] = goertzel_result(&s->out[i]);
+            if (energy[i] >= energy[best])
+            {
+                second_best = best;
+                best = i;
+            }
+            else if (energy[i] >= energy[second_best])
+            {
+                second_best = i;
+            }
+        }
+        /* Basic signal level and twist tests */
+        hit = 0;
+        if (energy[best] >= BELL_MF_THRESHOLD
+            &&
+            energy[second_best] >= BELL_MF_THRESHOLD
+            &&
+            energy[best] < energy[second_best]*BELL_MF_TWIST
+            &&
+            energy[best]*BELL_MF_TWIST > energy[second_best])
+        {
+            /* Relative peak test */
+            hit = 'X';
+            for (i = 0;  i < 6;  i++)
+            {
+                if (i != best  &&  i != second_best)
+                {
+                    if (energy[i]*BELL_MF_RELATIVE_PEAK >= energy[second_best])
+                    {
+                        /* The best two are not clearly the best */
+                        hit = 0;
+                        break;
+                    }
+                }
+            }
+        }
+        if (hit)
+        {
+            /* Get the values into ascending order */
+            if (second_best < best)
+            {
+                i = best;
+                best = second_best;
+                second_best = i;
+            }
+            best = best*5 + second_best - 1;
+            hit = bell_mf_positions[best];
+            /* Look for two successive similar results */
+            /* The logic in the next test is:
+               For KP we need 4 successive identical clean detects, with
+               two blocks of something different preceeding it. For anything
+               else we need two successive identical clean detects, with
+               two blocks of something different preceeding it. */
+            if (hit == s->hits[4]
+                &&
+                hit == s->hits[3]
+                &&
+                   ((hit != '*'  &&  hit != s->hits[2]  &&  hit != s->hits[1])
+                    ||
+                    (hit == '*'  &&  hit == s->hits[2]  &&  hit != s->hits[1]  &&  hit != s->hits[0])))
+            {
+                if (s->current_digits < MAX_BELL_MF_DIGITS)
+                {
+                    s->digits[s->current_digits++] = (char) hit;
+                    s->digits[s->current_digits] = '\0';
+                    if (s->callback)
+                    {
+                        s->callback(s->callback_data, s->digits, s->current_digits);
+                        s->current_digits = 0;
+                    }
+                }
+                else
+                {
+                    s->lost_digits++;
+                }
+            }
+        }
+        s->hits[0] = s->hits[1];
+        s->hits[1] = s->hits[2];
+        s->hits[2] = s->hits[3];
+        s->hits[3] = s->hits[4];
+        s->hits[4] = hit;
+        /* Reinitialise the detector for the next block */
+        for (i = 0;  i < 6;  i++)
+            goertzel_reset(&s->out[i]);
+        s->current_sample = 0;
+    }
+    if (s->current_digits  &&  s->callback)
+    {
+        s->callback(s->callback_data, s->digits, s->current_digits);
+        s->digits[0] = '\0';
+        s->current_digits = 0;
+    }
+    return 0;
+}
+/*- End of function --------------------------------------------------------*/
+
+size_t bell_mf_rx_get(bell_mf_rx_state_t *s, char *buf, int max)
+{
+    if (max > s->current_digits)
+        max = s->current_digits;
+    if (max > 0)
+    {
+        memcpy(buf, s->digits, max);
+        memmove(s->digits, s->digits + max, s->current_digits - max);
+        s->current_digits -= max;
+    }
+    buf[max] = '\0';
+    return  max;
+}
+/*- End of function --------------------------------------------------------*/
+
+bell_mf_rx_state_t *bell_mf_rx_init(bell_mf_rx_state_t *s,
+                                    void (*callback)(void *user_data, const char *digits, int len),
+                                    void *user_data)
+{
+    int i;
+    static int initialised = FALSE;
+
+    if (!initialised)
+    {
+        for (i = 0;  i < 6;  i++)
+            make_goertzel_descriptor(&bell_mf_detect_desc[i], bell_mf_frequencies[i], 120);
+        initialised = TRUE;
+    }
+    s->callback = callback;
+    s->callback_data = user_data;
+
+    s->hits[0] = 
+    s->hits[1] =
+    s->hits[2] =
+    s->hits[3] = 
+    s->hits[4] = 0;
+
+    for (i = 0;  i < 6;  i++)
+        goertzel_init(&s->out[i], &bell_mf_detect_desc[i]);
+    s->current_sample = 0;
+    s->lost_digits = 0;
+    s->current_digits = 0;
+    s->digits[0] = '\0';
+    return s;
+}
+/*- End of function --------------------------------------------------------*/
+
+int r2_mf_rx(r2_mf_rx_state_t *s, const int16_t amp[], int samples)
+{
+    float energy[6];
+    float famp;
+    float v1;
+    int i;
+    int j;
+    int sample;
+    int best;
+    int second_best;
+    int hit;
+    int hit_char;
+    int limit;
+
+    hit = 0;
+    hit_char = 0;
+    for (sample = 0;  sample < samples;  sample = limit)
+    {
+        if ((samples - sample) >= (s->samples - s->current_sample))
+            limit = sample + (s->samples - s->current_sample);
+        else
+            limit = samples;
+        for (j = sample;  j < limit;  j++)
+        {
+            famp = amp[j];
+    
+            /* With GCC 2.95, the following unrolled code seems to take about 35%
+               (rough estimate) as long as a neat little 0-5 loop */
+            v1 = s->out[0].v2;
+            s->out[0].v2 = s->out[0].v3;
+            s->out[0].v3 = s->out[0].fac*s->out[0].v2 - v1 + famp;
+    
+            v1 = s->out[1].v2;
+            s->out[1].v2 = s->out[1].v3;
+            s->out[1].v3 = s->out[1].fac*s->out[1].v2 - v1 + famp;
+    
+            v1 = s->out[2].v2;
+            s->out[2].v2 = s->out[2].v3;
+            s->out[2].v3 = s->out[2].fac*s->out[2].v2 - v1 + famp;
+    
+            v1 = s->out[3].v2;
+            s->out[3].v2 = s->out[3].v3;
+            s->out[3].v3 = s->out[3].fac*s->out[3].v2 - v1 + famp;
+    
+            v1 = s->out[4].v2;
+            s->out[4].v2 = s->out[4].v3;
+            s->out[4].v3 = s->out[4].fac*s->out[4].v2 - v1 + famp;
+    
+            v1 = s->out[5].v2;
+            s->out[5].v2 = s->out[5].v3;
+            s->out[5].v3 = s->out[5].fac*s->out[5].v2 - v1 + famp;
+        }
+        s->current_sample += (limit - sample);
+        if (s->current_sample < s->samples)
+            continue;
+
+        /* We are at the end of an MF detection block */
+        /* Find the two highest energies */
+        energy[0] = goertzel_result(&s->out[0]);
+        energy[1] = goertzel_result(&s->out[1]);
+        if (energy[0] > energy[1])
+        {
+            best = 0;
+            second_best = 1;
+        }
+        else
+        {
+            best = 1;
+            second_best = 0;
+        }
+        
+        for (i = 2;  i < 6;  i++)
+        {
+            energy[i] = goertzel_result(&s->out[i]);
+            if (energy[i] >= energy[best])
+            {
+                second_best = best;
+                best = i;
+            }
+            else if (energy[i] >= energy[second_best])
+            {
+                second_best = i;
+            }
+        }
+        /* Basic signal level and twist tests */
+        hit = FALSE;
+        if (energy[best] >= R2_MF_THRESHOLD
+            &&
+            energy[second_best] >= R2_MF_THRESHOLD
+            &&
+            energy[best] < energy[second_best]*R2_MF_TWIST
+            &&
+            energy[best]*R2_MF_TWIST > energy[second_best])
+        {
+            /* Relative peak test */
+            hit = TRUE;
+            for (i = 0;  i < 6;  i++)
+            {
+                if (i != best  &&  i != second_best)
+                {
+                    if (energy[i]*R2_MF_RELATIVE_PEAK >= energy[second_best])
+                    {
+                        /* The best two are not clearly the best */
+                        hit = FALSE;
+                        break;
+                    }
+                }
+            }
+        }
+        if (hit)
+        {
+            /* Get the values into ascending order */
+            if (second_best < best)
+            {
+                i = best;
+                best = second_best;
+                second_best = i;
+            }
+            best = best*5 + second_best - 1;
+            hit_char = r2_mf_positions[best];
+        }
+        else
+        {
+            hit_char = 0;
+        }
+
+        /* Reinitialise the detector for the next block */
+        if (s->fwd)
+        {
+            for (i = 0;  i < 6;  i++)
+                goertzel_reset(&s->out[i]);
+        }
+        else
+        {
+            for (i = 0;  i < 6;  i++)
+                goertzel_reset(&s->out[i]);
+        }
+        s->current_sample = 0;
+    }
+    return hit_char;
+}
+/*- End of function --------------------------------------------------------*/
+
+r2_mf_rx_state_t *r2_mf_rx_init(r2_mf_rx_state_t *s, int fwd)
+{
+    int i;
+    static int initialised = FALSE;
+
+    s->fwd = fwd;
+
+    if (!initialised)
+    {
+        for (i = 0;  i < 6;  i++)
+        {
+            make_goertzel_descriptor(&mf_fwd_detect_desc[i], r2_mf_fwd_frequencies[i], 133);
+            make_goertzel_descriptor(&mf_back_detect_desc[i], r2_mf_back_frequencies[i], 133);
+        }
+        initialised = TRUE;
+    }
+    if (fwd)
+    {
+        for (i = 0;  i < 6;  i++)
+            goertzel_init(&s->out[i], &mf_fwd_detect_desc[i]);
+    }
+    else
+    {
+        for (i = 0;  i < 6;  i++)
+            goertzel_init(&s->out[i], &mf_back_detect_desc[i]);
+    }
+    s->samples = 133;
+    s->current_sample = 0;
+    return s;
+}
+/*- End of function --------------------------------------------------------*/
+/*- End of file ------------------------------------------------------------*/