--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/adsi.c	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,966 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * adsi.c - Analogue display service interfaces of various types, including
+ *          ADSI, TDD and most caller ID formats.
+ *
+ * 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: adsi.c,v 1.36 2006/11/19 14:07:23 steveu Exp $
+ */
+
+/*! \file */
+
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <inttypes.h>
+#include <stdlib.h>
+#include <stdio.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/logging.h"
+#include "spandsp/dds.h"
+#include "spandsp/power_meter.h"
+#include "spandsp/async.h"
+#include "spandsp/hdlc.h"
+#include "spandsp/fsk.h"
+#include "spandsp/tone_detect.h"
+#include "spandsp/tone_generate.h"
+#include "spandsp/dtmf.h"
+#include "spandsp/adsi.h"
+
+#define BAUDOT_FIGURE_SHIFT     0x1B
+#define BAUDOT_LETTER_SHIFT     0x1F
+
+#define SOH 0x01
+#define STX 0x02
+#define ETX 0x03
+#define DLE 0x10
+#define SUB 0x1A
+
+static uint8_t adsi_encode_baudot(adsi_tx_state_t *s, uint8_t ch);
+static uint8_t adsi_decode_baudot(adsi_rx_state_t *s, uint8_t ch);
+
+static int adsi_tx_get_bit(void *user_data)
+{
+    int bit;
+    adsi_tx_state_t *s;
+    
+    s = (adsi_tx_state_t *) user_data;
+    /* This is similar to the async. handling code in fsk.c, but a few special
+       things are needed in the preamble, and postamble of an ADSI message. */
+    if (s->bitno < 300)
+    {
+        /* Alternating bit preamble */
+        bit = s->bitno & 1;
+        s->bitno++;
+    }
+    else if (s->bitno < 300 + s->ones_len)
+    {
+        /* All 1s for receiver conditioning */
+        /* NB: The receiver is an async one. It needs a rest after the
+               alternating 1/0 sequence so it can reliably pick up on
+               the next start bit, and sync to the byte stream. */
+        /* The length of this period varies with the circumstance */
+        bit = 1;
+        s->bitno++;
+    }
+    else if (s->bitno < 300 + s->ones_len + 1)
+    {
+        if (s->bitpos == 0)
+        {
+            /* Start bit */
+            bit = 0;
+            s->bitpos++;
+        }
+        else if (s->bitpos < 9)
+        {
+            bit = (s->msg[s->byteno] >> (s->bitpos - 1)) & 1;
+            s->bitpos++;
+        }
+        else
+        {
+            /* Stop bit */
+            bit = 1;
+            s->bitpos = 0;
+            s->byteno++;
+            if (s->byteno > s->msg_len)
+                s->bitno++;
+        }
+    }
+    else if (s->bitno < 300 + s->ones_len + 5)
+    {
+        /* Extra stop bits beyond the last character, to meet the specs., and ensure
+           all bits are out of the DSP before we shut off the FSK modem. */
+        bit = 1;
+        s->bitno++;
+    }
+    else
+    {
+        bit = 2;
+        if (s->tx_signal_on)
+        {
+            /* The FSK should now be switched off. */
+            s->tx_signal_on = FALSE;
+            s->msg_len = 0;
+        }
+    }
+    return bit;
+}
+/*- End of function --------------------------------------------------------*/
+
+static int adsi_tdd_get_async_byte(void *user_data)
+{
+    adsi_tx_state_t *s;
+    
+    s = (adsi_tx_state_t *) user_data;
+    if (s->byteno < s->msg_len)
+        return s->msg[s->byteno++];
+    if (s->tx_signal_on)
+    {
+        /* The FSK should now be switched off. */
+        s->tx_signal_on = FALSE;
+        s->msg_len = 0;
+    }
+    return 0x1F;
+}
+/*- End of function --------------------------------------------------------*/
+
+static void adsi_rx_put_bit(void *user_data, int bit)
+{
+    adsi_rx_state_t *s;
+    int i;
+    int sum;
+
+    s = (adsi_rx_state_t *) user_data;
+    if (bit < 0)
+    {
+        /* Special conditions */
+        switch (bit)
+        {
+        case PUTBIT_CARRIER_UP:
+            span_log(&s->logging, SPAN_LOG_FLOW, "Carrier up.\n");
+            s->consecutive_ones = 0;
+            s->bitpos = 0;
+            s->in_progress = 0;
+            s->msg_len = 0;
+            s->baudot_shift = 0;
+            break;
+        case PUTBIT_CARRIER_DOWN:
+            span_log(&s->logging, SPAN_LOG_FLOW, "Carrier down.\n");
+            break;
+        default:
+            span_log(&s->logging, SPAN_LOG_WARNING, "Unexpected special put bit value - %d!\n", bit);
+            break;
+        }
+        return;
+    }
+    bit &= 1;
+    if (s->bitpos == 0)
+    {
+        if (bit == 0)
+        {
+            /* Start bit */
+            s->bitpos++;
+            if (s->consecutive_ones > 10)
+            {
+                /* This is a line idle condition, which means we should
+                   restart message acquisition */
+                s->msg_len = 0;
+            }
+            s->consecutive_ones = 0;
+        }
+        else
+        {
+            s->consecutive_ones++;
+        }
+    }
+    else if (s->bitpos <= 8)
+    {
+        s->in_progress >>= 1;
+        if (bit)
+            s->in_progress |= 0x80;
+        s->bitpos++;
+    }
+    else
+    {
+        /* Stop bit */
+        if (bit)
+        {
+            if (s->msg_len < 256)
+            {
+                if (s->standard == ADSI_STANDARD_JCLIP)
+                {
+                    if (s->msg_len == 0)
+                    {
+                        /* A message should start DLE SOH, but let's just check 
+                           we are starting with a DLE for now */
+                        if (s->in_progress == (0x80 | DLE))
+                            s->msg[s->msg_len++] = (uint8_t) s->in_progress;
+                    }
+                    else
+                    {
+                        s->msg[s->msg_len++] = (uint8_t) s->in_progress;
+                    }
+                    if (s->msg_len >= 11  &&  s->msg_len == ((s->msg[6] & 0x7F) + 11))
+                    {
+                        /* Test the CRC-16 */
+                        if (crc_itu16_calc(s->msg + 2, s->msg_len - 2, 0) == 0)
+                        {
+                            /* Strip off the parity bits. It doesn't seem
+                               worthwhile actually checking the parity if a
+                               CRC check has succeeded. */
+                            for (i = 0;  i < s->msg_len - 2;  i++)
+                                s->msg[i] &= 0x7F;
+                            /* Put everything, except the CRC octets */
+                            s->put_msg(s->user_data, s->msg, s->msg_len - 2);
+                        }
+                        else
+                        {
+                            span_log(&s->logging, SPAN_LOG_WARNING, "CRC failed\n");
+                        }
+                        s->msg_len = 0;
+                    }
+                }
+                else
+                {
+                    s->msg[s->msg_len++] = (uint8_t) s->in_progress;
+                    if (s->msg_len >= 3  &&  s->msg_len == (s->msg[1] + 3))
+                    {
+                        /* Test the checksum */
+                        sum = 0;
+                        for (i = 0;  i < s->msg_len - 1;  i++)
+                            sum += s->msg[i];
+                        if ((-sum & 0xFF) == s->msg[i])
+                            s->put_msg(s->user_data, s->msg, s->msg_len - 1);
+                        else
+                            span_log(&s->logging, SPAN_LOG_WARNING, "Sumcheck failed\n");
+                        s->msg_len = 0;
+                    }
+                }
+            }
+        }
+        else
+        {
+            s->framing_errors++;
+        }
+        s->bitpos = 0;
+        s->in_progress = 0;
+    }
+}
+/*- End of function --------------------------------------------------------*/
+
+static void adsi_tdd_put_async_byte(void *user_data, int byte)
+{
+    adsi_rx_state_t *s;
+    uint8_t octet;
+    
+    s = (adsi_rx_state_t *) user_data;
+    if (byte < 0)
+    {
+        /* Special conditions */
+        switch (byte)
+        {
+        case PUTBIT_CARRIER_UP:
+            span_log(&s->logging, SPAN_LOG_FLOW, "Carrier up.\n");
+            s->consecutive_ones = 0;
+            s->bitpos = 0;
+            s->in_progress = 0;
+            s->msg_len = 0;
+            s->baudot_shift = 0;
+            break;
+        case PUTBIT_CARRIER_DOWN:
+            span_log(&s->logging, SPAN_LOG_FLOW, "Carrier down.\n");
+            if (s->msg_len > 0)
+            {
+                /* Whatever we have to date constitutes the message */
+                s->put_msg(s->user_data, s->msg, s->msg_len);
+                s->msg_len = 0;
+            }
+            break;
+        default:
+            span_log(&s->logging, SPAN_LOG_WARNING, "Unexpected special put byte value - %d!\n", byte);
+            break;
+        }
+        return;
+    }
+    if ((octet = adsi_decode_baudot(s, (uint8_t) byte)))
+        s->msg[s->msg_len++] = octet;
+    if (s->msg_len >= 256)
+    {
+        s->put_msg(s->user_data, s->msg, s->msg_len);
+        s->msg_len = 0;
+    }
+}
+/*- End of function --------------------------------------------------------*/
+
+static void adsi_rx_dtmf(void *user_data, const char *digits, int len)
+{
+    adsi_rx_state_t *s;
+
+    s = (adsi_rx_state_t *) user_data;
+    if (s->msg_len == 0)
+    {
+        /* Message starting. Start a 10s timeout, to make things more noise
+           tolerant for a detector running continuously when on hook. */
+        s->in_progress = 80000;
+    }
+    for (  ;  len  &&  s->msg_len < 256;  len--)
+    {
+        if (*digits == '#')
+        {
+            s->put_msg(s->user_data, s->msg, s->msg_len);
+            s->msg_len = 0;
+        }
+        else
+        {
+            s->msg[s->msg_len++] = *digits++;
+        }
+    }
+}
+/*- End of function --------------------------------------------------------*/
+
+static void start_tx(adsi_tx_state_t *s)
+{
+    switch (s->standard)
+    {
+    case ADSI_STANDARD_CLASS:
+        fsk_tx_init(&(s->fsktx), &preset_fsk_specs[FSK_BELL202], adsi_tx_get_bit, s);
+        break;
+    case ADSI_STANDARD_CLIP:
+    case ADSI_STANDARD_ACLIP:
+    case ADSI_STANDARD_JCLIP:
+        fsk_tx_init(&(s->fsktx), &preset_fsk_specs[FSK_V23CH1], adsi_tx_get_bit, s);
+        break;
+    case ADSI_STANDARD_CLIP_DTMF:
+        dtmf_tx_init(&(s->dtmftx));
+        break;
+    case ADSI_STANDARD_TDD:
+        fsk_tx_init(&(s->fsktx), &preset_fsk_specs[FSK_WEITBRECHT], async_tx_get_bit, &(s->asynctx));
+        async_tx_init(&(s->asynctx), 5, ASYNC_PARITY_NONE, 2, FALSE, adsi_tdd_get_async_byte, s);
+        /* Schedule an explicit shift at the start of baudot transmission */
+        s->baudot_shift = 2;
+        break;
+    }
+    s->tx_signal_on = TRUE;
+}
+/*- End of function --------------------------------------------------------*/
+
+void adsi_rx(adsi_rx_state_t *s, const int16_t *amp, int len)
+{
+    switch (s->standard)
+    {
+    case ADSI_STANDARD_CLIP_DTMF:
+        /* Apply a message timeout. */
+        s->in_progress -= len;
+        if (s->in_progress <= 0)
+            s->msg_len = 0;
+        dtmf_rx(&(s->dtmfrx), amp, len);
+        break;
+    default:
+        fsk_rx(&(s->fskrx), amp, len);
+        break;
+    }
+}
+/*- End of function --------------------------------------------------------*/
+
+void adsi_rx_init(adsi_rx_state_t *s,
+                  int standard,
+                  put_msg_func_t put_msg,
+                  void *user_data)
+{
+    memset(s, 0, sizeof(*s));
+    s->put_msg = put_msg;
+    s->user_data = user_data;
+    switch (standard)
+    {
+    case ADSI_STANDARD_CLASS:
+        fsk_rx_init(&(s->fskrx), &preset_fsk_specs[FSK_BELL202], FALSE, adsi_rx_put_bit, s);
+        break;
+    case ADSI_STANDARD_CLIP:
+    case ADSI_STANDARD_ACLIP:
+    case ADSI_STANDARD_JCLIP:
+        fsk_rx_init(&(s->fskrx), &preset_fsk_specs[FSK_V23CH1], FALSE, adsi_rx_put_bit, s);
+        break;
+    case ADSI_STANDARD_CLIP_DTMF:
+        dtmf_rx_init(&(s->dtmfrx), adsi_rx_dtmf, s);
+        break;
+    case ADSI_STANDARD_TDD:
+        fsk_rx_init(&(s->fskrx), &preset_fsk_specs[FSK_WEITBRECHT], FALSE, async_rx_put_bit, &(s->asyncrx));
+        async_rx_init(&(s->asyncrx), 5, ASYNC_PARITY_NONE, 2, TRUE, adsi_tdd_put_async_byte, s);
+        break;
+    }
+    s->standard = standard;
+    span_log_init(&s->logging, SPAN_LOG_NONE, NULL);
+}
+/*- End of function --------------------------------------------------------*/
+
+int adsi_tx(adsi_tx_state_t *s, int16_t *amp, int max_len)
+{
+    int len;
+
+    len = tone_gen(&(s->alert_tone_gen), amp, max_len);
+    switch (s->standard)
+    {
+    case ADSI_STANDARD_CLIP_DTMF:
+        if (len < max_len)
+            len += dtmf_tx(&(s->dtmftx), amp, max_len - len);
+        break;
+    default:
+        if (len < max_len  &&  s->tx_signal_on)
+            len += fsk_tx(&(s->fsktx), amp + len, max_len - len);
+        break;
+    }
+    return len;
+}
+/*- End of function --------------------------------------------------------*/
+
+void adsi_send_alert_tone(adsi_tx_state_t *s)
+{
+    tone_gen_init(&(s->alert_tone_gen), &(s->alert_tone_desc));
+}
+/*- End of function --------------------------------------------------------*/
+
+int adsi_put_message(adsi_tx_state_t *s, uint8_t *msg, int len)
+{
+    int i;
+    int j;
+    int k;
+    int byte;
+    int parity;
+    int sum;
+    size_t ii;
+    uint16_t crc_value;
+
+    /* Don't inject a new message when a previous one is still in progress */
+    if (s->msg_len > 0)
+        return 0;
+    if (!s->tx_signal_on)
+    {
+        /* We need to restart the modem */
+        start_tx(s);
+    }
+    switch (s->standard)
+    {
+    case ADSI_STANDARD_CLIP_DTMF:
+        if (len >= 128)
+            return -1;
+        msg[len] = '\0';
+        len -= (int) dtmf_tx_put(&(s->dtmftx), (char *) msg);
+        break;
+    case ADSI_STANDARD_JCLIP:
+        if (len > 128 - 9)
+            return -1;
+        i = 0;
+        s->msg[i++] = DLE;
+        s->msg[i++] = SOH;
+        s->msg[i++] = 0x07; //header
+        s->msg[i++] = DLE;
+        s->msg[i++] = STX;
+        s->msg[i++] = msg[0];
+        s->msg[i++] = (uint8_t) (len - 2);
+        /* We might need to byte stuff the overall length, but the rest of the
+           message should already be stuffed. */
+        if (len - 2 == DLE)
+            s->msg[i++] = DLE;
+        memcpy(&s->msg[i], &msg[2], len - 2);
+        i += len - 2;
+        s->msg[i++] = DLE;
+        s->msg[i++] = ETX;
+        
+        /* Set the parity bits */
+        for (j = 0;  j < i;  j++)
+        {
+            byte = s->msg[j];
+            parity = 0;
+            for (k = 1;  k <= 7;  k++)
+                parity ^= (byte << k);
+            s->msg[j] = (s->msg[j] & 0x7F) | ((uint8_t) parity & 0x80);
+        }
+
+        crc_value = crc_itu16_calc(s->msg + 2, i - 2, 0);
+        s->msg[i++] = (uint8_t) (crc_value & 0xFF);
+        s->msg[i++] = (uint8_t) ((crc_value >> 8) & 0xFF);
+        s->msg_len = i;
+
+        s->ones_len = 80;
+        break;
+    case ADSI_STANDARD_TDD:
+        if (len > 255)
+            return -1;
+        memcpy(s->msg, msg, len);
+        s->msg_len = len;
+        break;
+    default:
+        if (len > 255)
+            return -1;
+        memcpy(s->msg, msg, len);
+        /* Force the length in case it is wrong */
+        s->msg[1] = (uint8_t) (len - 2);
+        /* Add the sumcheck */
+        sum = 0;
+        for (ii = 0;  ii < (size_t) len;  ii++)
+            sum += s->msg[ii];
+        s->msg[len] = (uint8_t) ((-sum) & 0xFF);
+        s->msg_len = len + 1;
+        s->ones_len = 80;
+        break;
+    }    
+    /* Prepare the bit sequencing */
+    s->byteno = 0;
+    s->bitpos = 0;
+    s->bitno = 0;
+    return len;
+}
+/*- End of function --------------------------------------------------------*/
+
+void adsi_tx_init(adsi_tx_state_t *s, int standard)
+{
+    memset(s, 0, sizeof(*s));
+    make_tone_gen_descriptor(&(s->alert_tone_desc),
+                             2130,
+                             -13,
+                             2750,
+                             -13,
+                             110,
+                             60,
+                             0,
+                             0,
+                             FALSE);
+    s->standard = standard;
+    span_log_init(&s->logging, SPAN_LOG_NONE, NULL);
+    start_tx(s);
+}
+/*- End of function --------------------------------------------------------*/
+
+static uint8_t adsi_encode_baudot(adsi_tx_state_t *s, uint8_t ch)
+{
+    static const uint8_t conv[128] =
+    {
+        0x00, /* NUL */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0x42, /* LF */
+        0xFF, /*   */
+        0xFF, /*   */
+        0x48, /* CR */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0xFF, /*   */
+        0x44, /*   */
+        0xFF, /* ! */
+        0xFF, /* " */
+        0x94, /* # */
+        0x89, /* $ */
+        0xFF, /* % */
+        0xFF, /* & */
+        0x85, /* ' */
+        0x8F, /* ( */
+        0x92, /* ) */
+        0x8B, /* * */
+        0x91, /* + */
+        0x8C, /* , */
+        0x83, /* - */
+        0x9C, /* . */
+        0x9D, /* / */
+        0x96, /* 0 */
+        0x97, /* 1 */
+        0x93, /* 2 */
+        0x81, /* 3 */
+        0x8A, /* 4 */
+        0x90, /* 5 */
+        0x95, /* 6 */
+        0x87, /* 7 */
+        0x86, /* 8 */
+        0x98, /* 9 */
+        0x8E, /* : */
+        0xFF, /* ; */
+        0xFF, /* < */
+        0x9E, /* = */
+        0xFF, /* > */
+        0x99, /* ? */
+        0xFF, /* @ */
+        0x03, /* A */
+        0x19, /* B */
+        0x0E, /* C */
+        0x09, /* D */
+        0x01, /* E */
+        0x0D, /* F */
+        0x1A, /* G */
+        0x14, /* H */
+        0x06, /* I */
+        0x0B, /* J */
+        0x0F, /* K */
+        0x12, /* L */
+        0x1C, /* M */
+        0x0C, /* N */
+        0x18, /* O */
+        0x16, /* P */
+        0x17, /* Q */
+        0x0A, /* R */
+        0x05, /* S */
+        0x10, /* T */
+        0x07, /* U */
+        0x1E, /* V */
+        0x13, /* W */
+        0x1D, /* X */
+        0x15, /* Y */
+        0x11, /* Z */
+        0xFF, /* [ */
+        0xFF, /* \ */
+        0xFF, /* ] */
+        0x9B, /* ^ */
+        0xFF, /* _ */
+        0xFF, /* ` */
+        0x03, /* a */
+        0x19, /* b */
+        0x0E, /* c */
+        0x09, /* d */
+        0x01, /* e */
+        0x0D, /* f */
+        0x1A, /* g */
+        0x14, /* h */
+        0x06, /* i */
+        0x0B, /* j */
+        0x0F, /* k */
+        0x12, /* l */
+        0x1C, /* m */
+        0x0C, /* n */
+        0x18, /* o */
+        0x16, /* p */
+        0x17, /* q */
+        0x0A, /* r */
+        0x05, /* s */
+        0x10, /* t */
+        0x07, /* u */
+        0x1E, /* v */
+        0x13, /* w */
+        0x1D, /* x */
+        0x15, /* y */
+        0x11, /* z */
+        0xFF, /* { */
+        0xFF, /* | */
+        0xFF, /* } */
+        0xFF, /* ~ */
+        0xFF, /* DEL */
+    };
+
+    ch = conv[ch];
+    if (ch != 0xFF)
+    {
+        if ((ch & 0x40))
+            return ch & 0x1F;
+        if ((ch & 0x80))
+        {
+            if (s->baudot_shift == 1)
+                return ch & 0x1F;
+            s->baudot_shift = 1;
+            return (BAUDOT_FIGURE_SHIFT << 5) | (ch & 0x1F);
+        }
+        else
+        {
+            if (s->baudot_shift == 0)
+                return ch & 0x1F;
+            s->baudot_shift = 0;
+            return (BAUDOT_LETTER_SHIFT << 5) | (ch & 0x1F);
+        }
+    }
+    return 0;
+}
+/*- End of function --------------------------------------------------------*/
+
+static uint8_t adsi_decode_baudot(adsi_rx_state_t *s, uint8_t ch)
+{
+    static const uint8_t conv[2][32] =
+    {
+        {"\000E\nA SIU\rDRJNFCKTZLWHYPQOBG^MXV^"},
+        {"\0003\n- '87\r$4*,*:(5+)2#6019?*^./=^"}
+    };
+
+    switch (ch)
+    {
+    case BAUDOT_FIGURE_SHIFT:
+        s->baudot_shift = 1;
+        break;
+    case BAUDOT_LETTER_SHIFT:
+        s->baudot_shift = 0;
+        break;
+    default:
+        return conv[s->baudot_shift][ch];
+    }
+    /* return 0 if we did not produce a character */
+    return 0;
+}
+/*- End of function --------------------------------------------------------*/
+
+int adsi_next_field(adsi_rx_state_t *s, const uint8_t *msg, int msg_len, int pos, uint8_t *field_type, uint8_t const **field_body, int *field_len)
+{
+    int i;
+
+    /* Return -1 for no more fields. Return -2 for message structure corrupt. */
+    switch (s->standard)
+    {
+    case ADSI_STANDARD_CLASS:
+    case ADSI_STANDARD_CLIP:
+    case ADSI_STANDARD_ACLIP:
+        if (pos >= msg_len)
+            return -1;
+        /* For MDMF type messages, these standards all use "IE" type fields - type,
+           length, contents - and similar headers */
+        if (pos <= 0)
+        {
+            /* Return the message type */
+            *field_type = msg[0];
+            *field_len = 0;
+            *field_body = NULL;
+            pos = 2;
+        }
+        else
+        {
+            if ((msg[0] & 0x80))
+            {
+                /* MDMF messages seem to always have a message type with the MSB set. Is that
+                   guaranteed? */
+                *field_type = msg[pos++];
+                *field_len = msg[pos++];
+                *field_body = msg + pos;
+            }
+            else
+            {
+                /* SDMF */
+                *field_type = 0;
+                *field_len = msg_len - pos;
+                *field_body = msg + pos;
+            }
+            pos += *field_len;
+        }
+        if (pos > msg_len)
+            return -2;
+        break;
+    case ADSI_STANDARD_JCLIP:
+        if (pos >= msg_len - 2)
+            return -1;
+        if (pos <= 0)
+        {
+            /* Return the message type */
+            pos = 5;
+            *field_type = msg[pos++];
+            if (*field_type == DLE)
+                pos++;
+            if (msg[pos++] == DLE)
+                pos++;
+            *field_len = 0;
+            *field_body = NULL;
+        }
+        else
+        {
+            *field_type = msg[pos++];
+            if (*field_type == DLE)
+                pos++;
+            *field_len = msg[pos++];
+            if (*field_len == DLE)
+                pos++;
+            /* TODO: we assume here that the body contains no DLE's that would have been stuffed */
+            *field_body = msg + pos;
+            pos += *field_len;
+        }
+        if (pos > msg_len - 2)
+            return -2;
+        break;
+    case ADSI_STANDARD_CLIP_DTMF:
+        if (pos >= msg_len)
+            return -1;
+        if (pos < 0)
+            pos = 0;
+        *field_type = msg[pos++];
+        *field_body = msg + pos;
+        i = pos;
+        while (i < msg_len  &&  msg[i] != '#')
+            i++;
+        *field_len = i - pos;
+        pos = i;
+        if (msg[pos] == '#')
+            pos++;
+        if (pos > msg_len)
+            return -2;
+        break;
+    case ADSI_STANDARD_TDD:
+        if (pos >= msg_len)
+            return -1;
+        *field_type = 0;
+        *field_body = msg;
+        *field_len = msg_len;
+        pos = msg_len;
+        break;
+    }
+    return pos;
+}
+/*- End of function --------------------------------------------------------*/
+
+int adsi_add_field(adsi_tx_state_t *s, uint8_t *msg, int len, uint8_t field_type, uint8_t const *field_body, int field_len)
+{
+    int i;
+    int x;
+
+    switch (s->standard)
+    {
+    case ADSI_STANDARD_CLASS:
+    case ADSI_STANDARD_CLIP:
+    case ADSI_STANDARD_ACLIP:
+        /* These standards all use "IE" type fields - type, length, value - and similar headers */
+        if (len <= 0)
+        {
+            /* Initialise a new message. The field type is actually the message type. */
+            msg[0] = field_type;
+            msg[1] = 0;
+            len = 2;
+        }
+        else
+        {
+            /* Add to a message in progress. */
+            if (field_type)
+            {
+                msg[len++] = field_type;
+                msg[len++] = (uint8_t) field_len;
+                if (field_len == DLE)
+                    msg[len++] = (uint8_t) field_len;
+                memcpy(msg + len, field_body, field_len);
+                len += field_len;
+            }
+            else
+            {
+                /* No field type or length, for restricted single message formats */
+                memcpy(msg + len, field_body, field_len);
+                len += field_len;
+            }
+        }
+        break;
+    case ADSI_STANDARD_JCLIP:
+        /* This standard uses "IE" type fields - type, length, value - but escapes DLE characters,
+           to prevent immitation of a control octet. */
+        if (len <= 0)
+        {
+            /* Initialise a new message. The field type is actually the message type. */
+            msg[0] = field_type;
+            msg[1] = 0;
+            len = 2;
+        }
+        else
+        {
+            /* Add to a message in progress. */
+            msg[len++] = field_type;
+            if (field_type == DLE)
+                msg[len++] = field_type;
+            msg[len++] = (uint8_t) field_len;
+            if (field_len == DLE)
+                msg[len++] = (uint8_t) field_len;
+            for (i = 0;  i < field_len;  i++)
+            {
+                msg[len++] = field_body[i];
+                if (field_body[i] == DLE)
+                    msg[len++] = field_body[i];
+            }
+        }
+        break;
+    case ADSI_STANDARD_CLIP_DTMF:
+        if (len < 0)
+        {
+            len = 0;
+        }
+        else
+        {
+            msg[len] = field_type;
+            memcpy(msg + len + 1, field_body, field_len);
+            msg[len + field_len + 1] = '#';
+            len += (field_len + 2);
+        }
+        break;
+    case ADSI_STANDARD_TDD:
+        if (len < 0)
+            len = 0;
+        for (i = 0;  i < field_len;  i++)
+        {
+            if ((x = adsi_encode_baudot(s, field_body[i])))
+            {
+                if ((x & 0x3E0))
+                    msg[len++] = (uint8_t) ((x >> 5) & 0x1F);
+                msg[len++] = (uint8_t) (x & 0x1F);
+            }
+        }
+        break;
+    }
+
+    return len;
+}
+/*- End of function --------------------------------------------------------*/
+
+const char *adsi_standard_to_str(int standard)
+{
+    switch (standard)
+    {
+    case ADSI_STANDARD_CLASS:
+        return "CLASS";
+    case ADSI_STANDARD_CLIP:
+        return "CLIP";
+    case ADSI_STANDARD_ACLIP:
+        return "A-CLIP";
+    case ADSI_STANDARD_JCLIP:
+        return "J-CLIP";
+    case ADSI_STANDARD_CLIP_DTMF:
+        return "CLIP-DTMF";
+    case ADSI_STANDARD_TDD:
+        return "TDD";
+    }
+    return "???";
+}
+/*- End of function --------------------------------------------------------*/
+/*- End of file ------------------------------------------------------------*/