--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.6pre17/src/spandsp/modem_connect_tones.h	Fri Jun 25 15:50:58 2010 +0200
@@ -0,0 +1,177 @@
+/*
+ * 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 Lesser General Public License version 2.1,
+ * 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser 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 1.24 2009/06/02 16:03:56 steveu Exp $
+ */
+ 
+/*! \file */
+
+#if !defined(_SPANDSP_MODEM_CONNECT_TONES_H_)
+#define _SPANDSP_MODEM_CONNECT_TONES_H_
+
+/*! \page modem_connect_tones_page Modem connect 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 up 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. This is the echo
+canceller disable tone.
+
+The tone detector's design assumes the channel is free of any DC component.
+
+\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 for our purpose. 
+*/
+
+enum
+{
+    /*! \brief This is reported when a tone stops. */
+    MODEM_CONNECT_TONES_NONE = 0,
+    /*! \brief CNG tone is a pure 1100Hz tone, in 0.5s bursts, with 3s silences in between. The
+               bursts repeat for as long as is required. */
+    MODEM_CONNECT_TONES_FAX_CNG = 1,
+    /*! \brief ANS tone is a pure continuous 2100Hz+-15Hz tone for 3.3s+-0.7s. */
+    MODEM_CONNECT_TONES_ANS = 2,
+    /*! \brief ANS with phase reversals tone is a 2100Hz+-15Hz tone for 3.3s+-0.7s, with a 180 degree
+               phase jump every 450ms+-25ms. */
+    MODEM_CONNECT_TONES_ANS_PR = 3,
+    /*! \brief The ANSam tone is a version of ANS with 20% of 15Hz+-0.1Hz AM modulation, as per V.8 */
+    MODEM_CONNECT_TONES_ANSAM = 4,
+    /*! \brief The ANSam with phase reversals tone is a version of ANS_PR with 20% of 15Hz+-0.1Hz AM
+               modulation, as per V.8 */
+    MODEM_CONNECT_TONES_ANSAM_PR = 5,
+    /*! \brief FAX preamble in a string of V.21 HDLC flag octets. */
+    MODEM_CONNECT_TONES_FAX_PREAMBLE = 6,
+    /*! \brief CED tone is the same as ANS tone. FAX preamble in a string of V.21 HDLC flag octets.
+               This is only valid as a tone type to receive. It is never reported as a detected tone
+               type. The report will either be for FAX preamble or CED/ANS tone. */
+    MODEM_CONNECT_TONES_FAX_CED_OR_PREAMBLE = 7
+};
+
+/*! \brief FAX CED tone is the same as ANS tone. */
+#define MODEM_CONNECT_TONES_FAX_CED MODEM_CONNECT_TONES_ANS
+
+/*!
+    Modem connect tones generator descriptor. This defines the state
+    of a single working instance of the tone generator.
+*/
+typedef struct modem_connect_tones_tx_state_s 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 modem_connect_tones_rx_state_s modem_connect_tones_rx_state_t;
+
+#if defined(__cplusplus)
+extern "C"
+{
+#endif
+
+/*! \brief Initialise an instance of the modem connect tones generator.
+    \param s The context.
+*/
+SPAN_DECLARE(modem_connect_tones_tx_state_t *) modem_connect_tones_tx_init(modem_connect_tones_tx_state_t *s,
+                                                                           int tone_type);
+
+/*! \brief Release an instance of the modem connect tones generator.
+    \param s The context.
+    \return 0 for OK, else -1.
+*/
+SPAN_DECLARE(int) modem_connect_tones_tx_release(modem_connect_tones_tx_state_t *s);
+
+/*! \brief Free an instance of the modem connect tones generator.
+    \param s The context.
+    \return 0 for OK, else -1.
+*/
+SPAN_DECLARE(int) modem_connect_tones_tx_free(modem_connect_tones_tx_state_t *s);
+
+/*! \brief Generate a block of modem connect tones 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.
+*/
+SPAN_DECLARE_NONSTD(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.
+*/
+SPAN_DECLARE_NONSTD(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.
+*/
+SPAN_DECLARE(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.
+*/
+SPAN_DECLARE(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);
+
+/*! \brief Release an instance of the modem connect tones detector.
+    \param s The context.
+    \return 0 for OK, else -1. */
+SPAN_DECLARE(int) modem_connect_tones_rx_release(modem_connect_tones_rx_state_t *s);
+
+/*! \brief Free an instance of the modem connect tones detector.
+    \param s The context.
+    \return 0 for OK, else -1. */
+SPAN_DECLARE(int) modem_connect_tones_rx_free(modem_connect_tones_rx_state_t *s);
+
+SPAN_DECLARE(const char *) modem_connect_tone_to_str(int tone);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/