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 1.54 2008/10/13 13:14:01 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 #define V27TER_EQUALIZER_PRE_LEN 16 /* This much before the real event */ 00052 #define V27TER_EQUALIZER_POST_LEN 14 /* This much after the real event (must be even) */ 00053 00054 #define V27TER_RX_4800_FILTER_STEPS 27 00055 #define V27TER_RX_2400_FILTER_STEPS 27 00056 00057 #if V27TER_RX_4800_FILTER_STEPS > V27TER_RX_2400_FILTER_STEPS 00058 #define V27TER_RX_FILTER_STEPS V27TER_RX_4800_FILTER_STEPS 00059 #else 00060 #define V27TER_RX_FILTER_STEPS V27TER_RX_2400_FILTER_STEPS 00061 #endif 00062 00063 /*! 00064 V.27ter modem receive side descriptor. This defines the working state for a 00065 single instance of a V.27ter modem receiver. 00066 */ 00067 typedef struct v27ter_rx_state_s v27ter_rx_state_t; 00068 00069 #if defined(__cplusplus) 00070 extern "C" 00071 { 00072 #endif 00073 00074 /*! Initialise a V.27ter modem receive context. 00075 \brief Initialise a V.27ter modem receive context. 00076 \param s The modem context. 00077 \param bit_rate The bit rate of the modem. Valid values are 2400 and 4800. 00078 \param put_bit The callback routine used to put the received data. 00079 \param user_data An opaque pointer passed to the put_bit routine. 00080 \return A pointer to the modem context, or NULL if there was a problem. */ 00081 v27ter_rx_state_t *v27ter_rx_init(v27ter_rx_state_t *s, int bit_rate, put_bit_func_t put_bit, void *user_data); 00082 00083 /*! Reinitialise an existing V.27ter modem receive context. 00084 \brief Reinitialise an existing V.27ter modem receive context. 00085 \param s The modem context. 00086 \param bit_rate The bit rate of the modem. Valid values are 2400 and 4800. 00087 \param old_train TRUE if a previous trained values are to be reused. 00088 \return 0 for OK, -1 for bad parameter */ 00089 int v27ter_rx_restart(v27ter_rx_state_t *s, int bit_rate, int old_train); 00090 00091 /*! Free a V.27ter modem receive context. 00092 \brief Free a V.27ter modem receive context. 00093 \param s The modem context. 00094 \return 0 for OK */ 00095 int v27ter_rx_free(v27ter_rx_state_t *s); 00096 00097 logging_state_t *v27ter_rx_get_logging_state(v27ter_rx_state_t *s); 00098 00099 /*! Change the put_bit function associated with a V.27ter modem receive context. 00100 \brief Change the put_bit function associated with a V.27ter modem receive context. 00101 \param s The modem context. 00102 \param put_bit The callback routine used to handle received bits. 00103 \param user_data An opaque pointer. */ 00104 void v27ter_rx_set_put_bit(v27ter_rx_state_t *s, put_bit_func_t put_bit, void *user_data); 00105 00106 /*! Change the modem status report function associated with a V.27ter modem receive context. 00107 \brief Change the modem status report function associated with a V.27ter modem receive context. 00108 \param s The modem context. 00109 \param handler The callback routine used to report modem status changes. 00110 \param user_data An opaque pointer. */ 00111 void v27ter_rx_set_modem_status_handler(v27ter_rx_state_t *s, modem_rx_status_func_t handler, void *user_data); 00112 00113 /*! Process a block of received V.27ter modem audio samples. 00114 \brief Process a block of received V.27ter modem audio samples. 00115 \param s The modem context. 00116 \param amp The audio sample buffer. 00117 \param len The number of samples in the buffer. 00118 \return The number of samples unprocessed. 00119 */ 00120 int v27ter_rx(v27ter_rx_state_t *s, const int16_t amp[], int len); 00121 00122 /*! Get a snapshot of the current equalizer coefficients. 00123 \brief Get a snapshot of the current equalizer coefficients. 00124 \param coeffs The vector of complex coefficients. 00125 \return The number of coefficients in the vector. */ 00126 int v27ter_rx_equalizer_state(v27ter_rx_state_t *s, complexf_t **coeffs); 00127 00128 /*! Get the current received carrier frequency. 00129 \param s The modem context. 00130 \return The frequency, in Hertz. */ 00131 float v27ter_rx_carrier_frequency(v27ter_rx_state_t *s); 00132 00133 /*! Get the current symbol timing correction since startup. 00134 \param s The modem context. 00135 \return The correction. */ 00136 float v27ter_rx_symbol_timing_correction(v27ter_rx_state_t *s); 00137 00138 /*! Get a current received signal power. 00139 \param s The modem context. 00140 \return The signal power, in dBm0. */ 00141 float v27ter_rx_signal_power(v27ter_rx_state_t *s); 00142 00143 /*! Set the power level at which the carrier detection will cut in 00144 \param s The modem context. 00145 \param cutoff The signal cutoff power, in dBm0. */ 00146 void v27ter_rx_signal_cutoff(v27ter_rx_state_t *s, float cutoff); 00147 00148 /*! Set a handler routine to process QAM status reports 00149 \param s The modem context. 00150 \param handler The handler routine. 00151 \param user_data An opaque pointer passed to the handler routine. */ 00152 void v27ter_rx_set_qam_report_handler(v27ter_rx_state_t *s, qam_report_handler_t handler, void *user_data); 00153 00154 #if defined(__cplusplus) 00155 } 00156 #endif 00157 00158 #endif 00159 /*- End of file ------------------------------------------------------------*/