--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/spandsp/modem_connect_tones.h	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,156 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * modem_connect_tones.c - Generation and detection of tones
+ * associated with modems calling and answering calls.
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2006 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: modem_connect_tones.h,v 1.4 2006/10/24 13:45:28 steveu Exp $
+ */
+ 
+/*! \file */
+
+#if !defined(_MODEM_CONNECT_TONES_H_)
+#define _MODEM_CONNECT_TONES_H_
+
+/*! \page modem_connect_tones_page Echo cancellor disable tone detection
+
+\section modem_connect_tones_page_sec_1 What does it do?
+Some telephony terminal equipment, such as modems, require a channel which is as
+clear as possible. They use their own echo cancellation. If the network is also
+performing echo cancellation the two cancellors can end of squabbling about the
+nature of the channel, with bad results. A special tone is defined which should
+cause the network to disable any echo cancellation processes. 
+
+\section modem_connect_tones_page_sec_2 How does it work?
+A sharp notch filter is implemented as a single bi-quad section. The presence of
+the 2100Hz disable tone is detected by comparing the notched filtered energy
+with the unfiltered energy. If the notch filtered energy is much lower than the
+unfiltered energy, then a large proportion of the energy must be at the notch
+frequency. This type of detector may seem less intuitive than using a narrow
+bandpass filter to isolate the energy at the notch freqency. However, a sharp
+bandpass implemented as an IIR filter rings badly, The reciprocal notch filter
+is very well behaved. 
+*/
+
+enum
+{
+    MODEM_CONNECT_TONES_FAX_CNG,
+    MODEM_CONNECT_TONES_FAX_CED,
+    MODEM_CONNECT_TONES_EC_DISABLE,
+    /*! \brief The version of EC disable with some 15Hz AM content, as in V.8 */
+    MODEM_CONNECT_TONES_EC_DISABLE_MOD,
+};
+
+/*!
+    Modem connect tones generator descriptor. This defines the state
+    of a single working instance of the tone generator.
+*/
+typedef struct
+{
+    int tone_type;
+    
+    tone_gen_state_t tone_tx;
+    uint32_t tone_phase;
+    int32_t tone_phase_rate;
+    int level;
+    /*! \brief Countdown to the next phase hop */
+    int hop_timer;
+    uint32_t mod_phase;
+    int32_t mod_phase_rate;
+    int mod_level;
+} modem_connect_tones_tx_state_t;
+
+/*!
+    Modem connect tones receiver descriptor. This defines the state
+    of a single working instance of the tone detector.
+*/
+typedef struct
+{
+    int tone_type;
+    tone_report_func_t tone_callback;
+    void *callback_data;
+
+    float z1;
+    float z2;
+    int notch_level;
+    int channel_level;
+    int tone_present;
+    int tone_cycle_duration;
+    int good_cycles;
+    int hit;
+} modem_connect_tones_rx_state_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*! \brief Initialse an instance of the echo canceller disable tone generator.
+    \param s The context.
+*/
+modem_connect_tones_tx_state_t *modem_connect_tones_tx_init(modem_connect_tones_tx_state_t *s,
+                                                            int tone_type);
+
+/*! \brief Generate a block of echo canceller disable tone samples.
+    \param s The context.
+    \param amp An array of signal samples.
+    \param len The number of samples to generate.
+    \return The number of samples generated.
+*/
+int modem_connect_tones_tx(modem_connect_tones_tx_state_t *s,
+                           int16_t amp[],
+                           int len);
+
+/*! \brief Process a block of samples through an instance of the modem_connect
+           tones detector.
+    \param s The context.
+    \param amp An array of signal samples.
+    \param len The number of samples in the array.
+    \return The number of unprocessed samples.
+*/
+int modem_connect_tones_rx(modem_connect_tones_rx_state_t *s,
+                           const int16_t amp[],
+                           int len);
+                             
+/*! \brief Test if a modem_connect tone has been detected.
+    \param s The context.
+    \return TRUE if tone is detected, else FALSE.
+*/
+int modem_connect_tones_rx_get(modem_connect_tones_rx_state_t *s);
+
+/*! \brief Initialise an instance of the modem_connect tones detector.
+    \param s The context.
+    \param tone_type The type of connect tone being tested for.
+    \param tone_callback An optional callback routine, used to report tones
+    \param user_data An opaque pointer passed to the callback routine,
+    \return A pointer to the context.
+*/
+modem_connect_tones_rx_state_t *modem_connect_tones_rx_init(modem_connect_tones_rx_state_t *s,
+                                                            int tone_type,
+                                                            tone_report_func_t tone_callback,
+                                                            void *user_data);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/