v27ter_rx.h

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00001 /*
00002  * SpanDSP - a series of DSP components for telephony
00003  *
00004  * v27ter_rx.h - ITU V.27ter modem receive part
00005  *
00006  * Written by Steve Underwood <steveu@coppice.org>
00007  *
00008  * Copyright (C) 2003 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: v27ter_rx.h,v 1.59 2009/04/12 09:12:11 steveu Exp $
00026  */
00027 
00028 /*! \file */
00029 
00030 #if !defined(_SPANDSP_V27TER_RX_H_)
00031 #define _SPANDSP_V27TER_RX_H_
00032 
00033 /*! \page v27ter_rx_page The V.27ter receiver
00034 
00035 \section v27ter_rx_page_sec_1 What does it do?
00036 The V.27ter receiver implements the receive side of a V.27ter modem. This can operate
00037 at data rates of 4800 and 2400 bits/s. The audio input is a stream of 16 bit samples,
00038 at 8000 samples/second. The transmit and receive side of V.27ter modems operate
00039 independantly. V.27ter is mostly used for FAX transmission, where it provides the
00040 standard 4800 bits/s rate (the 2400 bits/s mode is not used for FAX). 
00041 
00042 \section v27ter_rx_page_sec_2 How does it work?
00043 V.27ter defines two modes of operation. One uses 8-PSK at 1600 baud, giving 4800bps.
00044 The other uses 4-PSK at 1200 baud, giving 2400bps. A training sequence is specified
00045 at the start of transmission, which makes the design of a V.27ter receiver relatively
00046 straightforward.
00047 */
00048 
00049 /* Target length for the equalizer is about 43 taps for 4800bps and 32 taps for 2400bps
00050    to deal with the worst stuff in V.56bis. */
00051 /*! Samples before the target position in the equalizer buffer */
00052 #define V27TER_EQUALIZER_PRE_LEN        16  /* This much before the real event */
00053 /*! Samples after the target position in the equalizer buffer */
00054 #define V27TER_EQUALIZER_POST_LEN       14  /* This much after the real event (must be even) */
00055 
00056 /*! The number of taps in the 4800bps pulse shaping/bandpass filter */
00057 #define V27TER_RX_4800_FILTER_STEPS     27
00058 /*! The number of taps in the 2400bps pulse shaping/bandpass filter */
00059 #define V27TER_RX_2400_FILTER_STEPS     27
00060 
00061 #if V27TER_RX_4800_FILTER_STEPS > V27TER_RX_2400_FILTER_STEPS
00062 #define V27TER_RX_FILTER_STEPS V27TER_RX_4800_FILTER_STEPS
00063 #else
00064 #define V27TER_RX_FILTER_STEPS V27TER_RX_2400_FILTER_STEPS
00065 #endif
00066 
00067 /*!
00068     V.27ter modem receive side descriptor. This defines the working state for a
00069     single instance of a V.27ter modem receiver.
00070 */
00071 typedef struct v27ter_rx_state_s v27ter_rx_state_t;
00072 
00073 #if defined(__cplusplus)
00074 extern "C"
00075 {
00076 #endif
00077 
00078 /*! Initialise a V.27ter modem receive context.
00079     \brief Initialise a V.27ter modem receive context.
00080     \param s The modem context.
00081     \param bit_rate The bit rate of the modem. Valid values are 2400 and 4800.
00082     \param put_bit The callback routine used to put the received data.
00083     \param user_data An opaque pointer passed to the put_bit routine.
00084     \return A pointer to the modem context, or NULL if there was a problem. */
00085 SPAN_DECLARE(v27ter_rx_state_t *) v27ter_rx_init(v27ter_rx_state_t *s, int bit_rate, put_bit_func_t put_bit, void *user_data);
00086 
00087 /*! Reinitialise an existing V.27ter modem receive context.
00088     \brief Reinitialise an existing V.27ter modem receive context.
00089     \param s The modem context.
00090     \param bit_rate The bit rate of the modem. Valid values are 2400 and 4800.
00091     \param old_train TRUE if a previous trained values are to be reused.
00092     \return 0 for OK, -1 for bad parameter */
00093 SPAN_DECLARE(int) v27ter_rx_restart(v27ter_rx_state_t *s, int bit_rate, int old_train);
00094 
00095 /*! Release a V.27ter modem receive context.
00096     \brief Release a V.27ter modem receive context.
00097     \param s The modem context.
00098     \return 0 for OK */
00099 SPAN_DECLARE(int) v27ter_rx_release(v27ter_rx_state_t *s);
00100 
00101 /*! Free a V.27ter modem receive context.
00102     \brief Free a V.27ter modem receive context.
00103     \param s The modem context.
00104     \return 0 for OK */
00105 SPAN_DECLARE(int) v27ter_rx_free(v27ter_rx_state_t *s);
00106 
00107 /*! Get the logging context associated with a V.27ter modem receive context.
00108     \brief Get the logging context associated with a V.27ter modem receive context.
00109     \param s The modem context.
00110     \return A pointer to the logging context */
00111 SPAN_DECLARE(logging_state_t *) v27ter_rx_get_logging_state(v27ter_rx_state_t *s);
00112 
00113 /*! Change the put_bit function associated with a V.27ter modem receive context.
00114     \brief Change the put_bit function associated with a V.27ter modem receive context.
00115     \param s The modem context.
00116     \param put_bit The callback routine used to handle received bits.
00117     \param user_data An opaque pointer. */
00118 SPAN_DECLARE(void) v27ter_rx_set_put_bit(v27ter_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
00119 
00120 /*! Change the modem status report function associated with a V.27ter modem receive context.
00121     \brief Change the modem status report function associated with a V.27ter modem receive context.
00122     \param s The modem context.
00123     \param handler The callback routine used to report modem status changes.
00124     \param user_data An opaque pointer. */
00125 SPAN_DECLARE(void) v27ter_rx_set_modem_status_handler(v27ter_rx_state_t *s, modem_rx_status_func_t handler, void *user_data);
00126 
00127 /*! Process a block of received V.27ter modem audio samples.
00128     \brief Process a block of received V.27ter modem audio samples.
00129     \param s The modem context.
00130     \param amp The audio sample buffer.
00131     \param len The number of samples in the buffer.
00132     \return The number of samples unprocessed.
00133 */
00134 SPAN_DECLARE(int) v27ter_rx(v27ter_rx_state_t *s, const int16_t amp[], int len);
00135 
00136 /*! Fake processing of a missing block of received V.27ter modem audio samples.
00137     (e.g due to packet loss).
00138     \brief Fake processing of a missing block of received V.27ter modem audio samples.
00139     \param s The modem context.
00140     \param len The number of samples to fake.
00141     \return The number of samples unprocessed.
00142 */
00143 SPAN_DECLARE(int) v27ter_rx_fillin(v27ter_rx_state_t *s, int len);
00144 
00145 /*! Get a snapshot of the current equalizer coefficients.
00146     \brief Get a snapshot of the current equalizer coefficients.
00147     \param coeffs The vector of complex coefficients.
00148     \return The number of coefficients in the vector. */
00149 SPAN_DECLARE(int) v27ter_rx_equalizer_state(v27ter_rx_state_t *s, complexf_t **coeffs);
00150 
00151 /*! Get the current received carrier frequency.
00152     \param s The modem context.
00153     \return The frequency, in Hertz. */
00154 SPAN_DECLARE(float) v27ter_rx_carrier_frequency(v27ter_rx_state_t *s);
00155 
00156 /*! Get the current symbol timing correction since startup.
00157     \param s The modem context.
00158     \return The correction. */
00159 SPAN_DECLARE(float) v27ter_rx_symbol_timing_correction(v27ter_rx_state_t *s);
00160 
00161 /*! Get a current received signal power.
00162     \param s The modem context.
00163     \return The signal power, in dBm0. */
00164 SPAN_DECLARE(float) v27ter_rx_signal_power(v27ter_rx_state_t *s);
00165 
00166 /*! Set the power level at which the carrier detection will cut in
00167     \param s The modem context.
00168     \param cutoff The signal cutoff power, in dBm0. */
00169 SPAN_DECLARE(void) v27ter_rx_signal_cutoff(v27ter_rx_state_t *s, float cutoff);
00170 
00171 /*! Set a handler routine to process QAM status reports
00172     \param s The modem context.
00173     \param handler The handler routine.
00174     \param user_data An opaque pointer passed to the handler routine. */
00175 SPAN_DECLARE(void) v27ter_rx_set_qam_report_handler(v27ter_rx_state_t *s, qam_report_handler_t handler, void *user_data);
00176 
00177 #if defined(__cplusplus)
00178 }
00179 #endif
00180 
00181 #endif
00182 /*- End of file ------------------------------------------------------------*/

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