silence_gen.h

00001 /*
00002  * SpanDSP - a series of DSP components for telephony
00003  *
00004  * silence_gen.c - A silence generator, for inserting timed silences.
00005  *
00006  * Written by Steve Underwood <steveu@coppice.org>
00007  *
00008  * Copyright (C) 2006 Steve Underwood
00009  *
00010  * All rights reserved.
00011  *
00012  * This program is free software; you can redistribute it and/or modify
00013  * it under the terms of the GNU Lesser General Public License version 2.1,
00014  * as published by the Free Software Foundation.
00015  *
00016  * This program is distributed in the hope that it will be useful,
00017  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00018  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00019  * GNU Lesser General Public License for more details.
00020  *
00021  * You should have received a copy of the GNU Lesser General Public
00022  * License along with this program; if not, write to the Free Software
00023  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
00024  *
00025  * $Id: silence_gen.h,v 1.19 2009/09/04 14:38:47 steveu Exp $
00026  */
00027 
00028 #if !defined(_SPANDSP_SILENCE_GEN_H_)
00029 #define _SPANDSP_SILENCE_GEN_H_
00030 
00031 typedef struct silence_gen_state_s silence_gen_state_t;
00032 
00033 #if defined(__cplusplus)
00034 extern "C"
00035 {
00036 #endif
00037 
00038 /*! Generate a block of silent audio samples.
00039     \brief Generate a block of silent audio samples.
00040     \param s The silence generator context.
00041     \param amp The audio sample buffer.
00042     \param max_len The number of samples to be generated.
00043     \return The number of samples actually generated. This will be zero when
00044             there is nothing to send.
00045 */
00046 SPAN_DECLARE_NONSTD(int) silence_gen(silence_gen_state_t *s, int16_t *amp, int max_len);
00047 
00048 /*! Set a silence generator context to output continuous silence.
00049     \brief Set a silence generator context to output continuous silence.
00050     \param s The silence generator context.
00051 */
00052 SPAN_DECLARE(void) silence_gen_always(silence_gen_state_t *s);
00053 
00054 /*! Set a silence generator context to output a specified period of silence.
00055     \brief Set a silence generator context to output a specified period of silence.
00056     \param s The silence generator context.
00057     \param silent_samples The number of samples to be generated.
00058 */
00059 SPAN_DECLARE(void) silence_gen_set(silence_gen_state_t *s, int silent_samples);
00060 
00061 /*! Alter the period of a silence generator context by a specified amount.
00062     \brief Alter the period of a silence generator context by a specified amount.
00063     \param s The silence generator context.
00064     \param silent_samples The number of samples to change the setting by. A positive number
00065                           increases the duration. A negative number reduces it. The duration
00066                           is prevented from going negative.
00067 */
00068 SPAN_DECLARE(void) silence_gen_alter(silence_gen_state_t *s, int silent_samples);
00069 
00070 /*! Find how long a silence generator context has to run.
00071     \brief Find how long a silence generator context has to run.
00072     \param s The silence generator context.
00073     \return The number of samples remaining.
00074 */
00075 SPAN_DECLARE(int) silence_gen_remainder(silence_gen_state_t *s);
00076 
00077 /*! Find the total silence generated to date by a silence generator context.
00078     \brief Find the total silence generated to date.
00079     \param s The silence generator context.
00080     \return The number of samples generated.
00081 */
00082 SPAN_DECLARE(int) silence_gen_generated(silence_gen_state_t *s);
00083 
00084 /*! Change the status reporting function associated with a silence generator context.
00085     \brief Change the status reporting function associated with a silence generator context.
00086     \param s The silence generator context.
00087     \param handler The callback routine used to report status changes.
00088     \param user_data An opaque pointer. */
00089 SPAN_DECLARE(void) silence_gen_status_handler(silence_gen_state_t *s, modem_tx_status_func_t handler, void *user_data);
00090 
00091 /*! Initialise a timed silence generator context.
00092     \brief Initialise a timed silence generator context.
00093     \param s The silence generator context.
00094     \param silent_samples The initial number of samples to set the silence to.
00095     \return A pointer to the silence generator context.
00096 */
00097 SPAN_DECLARE(silence_gen_state_t *) silence_gen_init(silence_gen_state_t *s, int silent_samples);
00098 
00099 SPAN_DECLARE(int) silence_gen_release(silence_gen_state_t *s);
00100 
00101 SPAN_DECLARE(int) silence_gen_free(silence_gen_state_t *s);
00102 
00103 /* The following dummy routines, to absorb data, don't really have a proper home,
00104    so they have been put here. */
00105 
00106 /*! A dummy routine to use as a receive callback, when we aren't really
00107     trying to process what is received. It just absorbs and ignores the
00108     data.
00109     \brief Dummy receive callback.
00110     \param user_data The context.
00111     \param amp The signal.buffer
00112     \param len The length of the signal buffer
00113     \return 0.
00114 */
00115 SPAN_DECLARE_NONSTD(int) span_dummy_rx(void *user_data, const int16_t amp[], int len);
00116 
00117 /*! A dummy routine to use as a signal modifier callback, when we aren't
00118     really trying to process the signal. It just returns without affecting
00119     anything.
00120     \brief Dummy signal modifier callback.
00121     \param user_data The context.
00122     \param amp The signal.buffer
00123     \param len The length of the signal buffer
00124     \return 0.
00125 */
00126 SPAN_DECLARE(int) span_dummy_mod(void *user_data, int16_t amp[], int len);
00127 
00128 /*! A dummy routine to use as a receive fillin callback, when we aren't really
00129     trying to process what is received. It just absorbs and ignores the
00130     request.
00131     \brief Dummy receive fillin callback.
00132     \param user_data The context.
00133     \param len The length of the signal buffer
00134     \return 0.
00135 */
00136 SPAN_DECLARE_NONSTD(int) span_dummy_rx_fillin(void *user_data, int len);
00137 
00138 #if defined(__cplusplus)
00139 }
00140 #endif
00141 
00142 #endif
00143 /*- End of file ------------------------------------------------------------*/

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