dsp_dtmf.c

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/*
 * DTMF decoder.
 *
 * Copyright            by Andreas Eversberg ([email protected])
 *          based on different decoders such as ISDN4Linux
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 *
 */

#include <linux/mISDNif.h>
#include <linux/mISDNdsp.h>
#include "core.h"
#include "dsp.h"

#define NCOEFF            8     /* number of frequencies to be analyzed */

/* For DTMF recognition:
 * 2 * cos(2 * PI * k / N) precalculated for all k
 */
static u64 cos2pik[NCOEFF] =
{
    /* k << 15 (source: hfc-4s/8s documentation (www.colognechip.de)) */
    55960, 53912, 51402, 48438, 38146, 32650, 26170, 18630
};

/* digit matrix */
static char dtmf_matrix[4][4] =
{
    {'1', '2', '3', 'A'},
    {'4', '5', '6', 'B'},
    {'7', '8', '9', 'C'},
    {'*', '0', '#', 'D'}
};

/* dtmf detection using goertzel algorithm
 * init function
 */
void dsp_dtmf_goertzel_init(struct dsp *dsp)
{
    dsp->dtmf.size = 0;
    dsp->dtmf.lastwhat = '\0';
    dsp->dtmf.lastdigit = '\0';
    dsp->dtmf.count = 0;
}

/* check for hardware or software features
 */
void dsp_dtmf_hardware(struct dsp *dsp)
{
    int hardware = 1;

    if (!dsp->dtmf.enable)
        return;

    if (!dsp->features.hfc_dtmf)
        hardware = 0;

    /* check for volume change */
    if (dsp->tx_volume) {
        if (dsp_debug & DEBUG_DSP_DTMF)
            printk(KERN_DEBUG "%s dsp %s cannot do hardware DTMF, "
                   "because tx_volume is changed\n",
                   __func__, dsp->name);
        hardware = 0;
    }
    if (dsp->rx_volume) {
        if (dsp_debug & DEBUG_DSP_DTMF)
            printk(KERN_DEBUG "%s dsp %s cannot do hardware DTMF, "
                   "because rx_volume is changed\n",
                   __func__, dsp->name);
        hardware = 0;
    }
    /* check if encryption is enabled */
    if (dsp->bf_enable) {
        if (dsp_debug & DEBUG_DSP_DTMF)
            printk(KERN_DEBUG "%s dsp %s cannot do hardware DTMF, "
                   "because encryption is enabled\n",
                   __func__, dsp->name);
        hardware = 0;
    }
    /* check if pipeline exists */
    if (dsp->pipeline.inuse) {
        if (dsp_debug & DEBUG_DSP_DTMF)
            printk(KERN_DEBUG "%s dsp %s cannot do hardware DTMF, "
                   "because pipeline exists.\n",
                   __func__, dsp->name);
        hardware = 0;
    }

    dsp->dtmf.hardware = hardware;
    dsp->dtmf.software = !hardware;
}


/*************************************************************
 * calculate the coefficients of the given sample and decode *
 *************************************************************/

/* the given sample is decoded. if the sample is not long enough for a
 * complete frame, the decoding is finished and continued with the next
 * call of this function.
 *
 * the algorithm is very good for detection with a minimum of errors. i
 * tested it allot. it even works with very short tones (40ms). the only
 * disadvantage is, that it doesn't work good with different volumes of both
 * tones. this will happen, if accoustically coupled dialers are used.
 * it sometimes detects tones during speech, which is normal for decoders.
 * use sequences to given commands during calls.
 *
 * dtmf - points to a structure of the current dtmf state
 * spl and len - the sample
 * fmt - 0 = alaw, 1 = ulaw, 2 = coefficients from HFC DTMF hw-decoder
 */

u8
*dsp_dtmf_goertzel_decode(struct dsp *dsp, u8 *data, int len, int fmt)
{
    u8 what;
    int size;
    signed short *buf;
    s32 sk, sk1, sk2;
    int k, n, i;
    s32 *hfccoeff;
    s32 result[NCOEFF], tresh, treshl;
    int lowgroup, highgroup;
    s64 cos2pik_;

    dsp->dtmf.digits[0] = '\0';

    /* Note: The function will loop until the buffer has not enough samples
     * left to decode a full frame.
     */
again:
    /* convert samples */
    size = dsp->dtmf.size;
    buf = dsp->dtmf.buffer;
    switch (fmt) {
    case 0: /* alaw */
    case 1: /* ulaw */
        while (size < DSP_DTMF_NPOINTS && len) {
            buf[size++] = dsp_audio_law_to_s32[*data++];
            len--;
        }
        break;

    case 2: /* HFC coefficients */
    default:
        if (len < 64) {
            if (len > 0)
                printk(KERN_ERR "%s: coefficients have invalid "
                       "size. (is=%d < must=%d)\n",
                       __func__, len, 64);
            return dsp->dtmf.digits;
        }
        hfccoeff = (s32 *)data;
        for (k = 0; k < NCOEFF; k++) {
            sk2 = (*hfccoeff++) >> 4;
            sk = (*hfccoeff++) >> 4;
            if (sk > 32767 || sk < -32767 || sk2 > 32767
                || sk2 < -32767)
                printk(KERN_WARNING
                       "DTMF-Detection overflow\n");
            /* compute |X(k)|**2 */
            result[k] =
                (sk * sk) -
                (((cos2pik[k] * sk) >> 15) * sk2) +
                (sk2 * sk2);
        }
        data += 64;
        len -= 64;
        goto coefficients;
        break;
    }
    dsp->dtmf.size = size;

    if (size < DSP_DTMF_NPOINTS)
        return dsp->dtmf.digits;

    dsp->dtmf.size = 0;

    /* now we have a full buffer of signed long samples - we do goertzel */
    for (k = 0; k < NCOEFF; k++) {
        sk = 0;
        sk1 = 0;
        sk2 = 0;
        buf = dsp->dtmf.buffer;
        cos2pik_ = cos2pik[k];
        for (n = 0; n < DSP_DTMF_NPOINTS; n++) {
            sk = ((cos2pik_ * sk1) >> 15) - sk2 + (*buf++);
            sk2 = sk1;
            sk1 = sk;
        }
        sk >>= 8;
        sk2 >>= 8;
        if (sk > 32767 || sk < -32767 || sk2 > 32767 || sk2 < -32767)
            printk(KERN_WARNING "DTMF-Detection overflow\n");
        /* compute |X(k)|**2 */
        result[k] =
            (sk * sk) -
            (((cos2pik[k] * sk) >> 15) * sk2) +
            (sk2 * sk2);
    }

    /* our (squared) coefficients have been calculated, we need to process
     * them.
     */
coefficients:
    tresh = 0;
    for (i = 0; i < NCOEFF; i++) {
        if (result[i] < 0)
            result[i] = 0;
        if (result[i] > dsp->dtmf.treshold) {
            if (result[i] > tresh)
                tresh = result[i];
        }
    }

    if (tresh == 0) {
        what = 0;
        goto storedigit;
    }

    if (dsp_debug & DEBUG_DSP_DTMFCOEFF) {
        s32 tresh_100 = tresh/100;

        if (tresh_100 == 0) {
            tresh_100 = 1;
            printk(KERN_DEBUG
                "tresh(%d) too small set tresh/100 to 1\n",
                tresh);
        }
        printk(KERN_DEBUG "a %3d %3d %3d %3d %3d %3d %3d %3d"
               " tr:%3d r %3d %3d %3d %3d %3d %3d %3d %3d\n",
               result[0] / 10000, result[1] / 10000, result[2] / 10000,
               result[3] / 10000, result[4] / 10000, result[5] / 10000,
               result[6] / 10000, result[7] / 10000, tresh / 10000,
               result[0] / (tresh_100), result[1] / (tresh_100),
               result[2] / (tresh_100), result[3] / (tresh_100),
               result[4] / (tresh_100), result[5] / (tresh_100),
               result[6] / (tresh_100), result[7] / (tresh_100));
    }

    /* calc digit (lowgroup/highgroup) */
    lowgroup = -1;
    highgroup = -1;
    treshl = tresh >> 3;  /* tones which are not on, must be below 9 dB */
    tresh = tresh >> 2;  /* touchtones must match within 6 dB */
    for (i = 0; i < NCOEFF; i++) {
        if (result[i] < treshl)
            continue;  /* ignore */
        if (result[i] < tresh) {
            lowgroup = -1;
            highgroup = -1;
            break;  /* noise in between */
        }
        /* good level found. This is allowed only one time per group */
        if (i < NCOEFF / 2) {
            /* lowgroup */
            if (lowgroup >= 0) {
                /* Bad. Another tone found. */
                lowgroup = -1;
                break;
            } else
                lowgroup = i;
        } else {
            /* higroup */
            if (highgroup >= 0) {
                /* Bad. Another tone found. */
                highgroup = -1;
                break;
            } else
                highgroup = i - (NCOEFF / 2);
        }
    }

    /* get digit or null */
    what = 0;
    if (lowgroup >= 0 && highgroup >= 0)
        what = dtmf_matrix[lowgroup][highgroup];

storedigit:
    if (what && (dsp_debug & DEBUG_DSP_DTMF))
        printk(KERN_DEBUG "DTMF what: %c\n", what);

    if (dsp->dtmf.lastwhat != what)
        dsp->dtmf.count = 0;

    /* the tone (or no tone) must remain 3 times without change */
    if (dsp->dtmf.count == 2) {
        if (dsp->dtmf.lastdigit != what) {
            dsp->dtmf.lastdigit = what;
            if (what) {
                if (dsp_debug & DEBUG_DSP_DTMF)
                    printk(KERN_DEBUG "DTMF digit: %c\n",
                           what);
                if ((strlen(dsp->dtmf.digits) + 1)
                    < sizeof(dsp->dtmf.digits)) {
                    dsp->dtmf.digits[strlen(
                            dsp->dtmf.digits) + 1] = '\0';
                    dsp->dtmf.digits[strlen(
                            dsp->dtmf.digits)] = what;
                }
            }
        }
    } else
        dsp->dtmf.count++;

    dsp->dtmf.lastwhat = what;

    goto again;
}