--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/spandsp/v27ter_tx.h	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,172 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * v27ter_tx.h - ITU V.27ter modem transmit part
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2003 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: v27ter_tx.h,v 1.25 2006/10/24 13:45:28 steveu Exp $
+ */
+
+/*! \file */
+
+#if !defined(_V27TER_TX_H_)
+#define _V27TER_TX_H_
+
+/*! \page v27ter_tx_page The V.27ter transmitter
+\section v27ter_tx_page_sec_1 What does it do?
+The V.27ter transmitter implements the transmit side of a V.27ter modem. This
+can operate at data rates of 4800 and 2400 bits/s. The audio output is a stream
+of 16 bit samples, at 8000 samples/second. The transmit and receive side of
+V.27ter modems operate independantly. V.27ter is used for FAX transmission,
+where it provides the standard 4800 and 2400 bits/s rates. 
+
+\section v27ter_tx_page_sec_2 How does it work?
+V.27ter uses DPSK modulation. A common method of producing a DPSK modulated
+signal is to use a sampling rate which is a multiple of the baud rate. The raw
+signal is then a series of complex pulses, each an integer number of samples
+long. These can be shaped, using a suitable complex filter, and multiplied by a
+complex carrier signal to produce the final DPSK signal for transmission. 
+
+The pulse shaping filter for V.27ter is defined in the spec. It is a root raised
+cosine filter with 50% excess bandwidth. 
+
+The sampling rate for our transmitter is defined by the channel - 8000 samples/s.
+This is a multiple of the baud rate at 4800 bits/s (8-PSK at 1600 baud, 5 samples per
+symbol), but not at 2400 bits/s (4-PSK at 1200 baud, 20/3 samples per symbol). The baud
+interval is actually 20/3 sample periods at 2400bis/s. A symmetric FIR is used to
+apply root raised cosine filtering in the 4800bits/s mode. In the 2400bits/s mode
+a polyphase FIR filter is used. This consists of 20 sets of coefficients, offering
+zero to 19/20ths of a baud phase shift as well as root raised cosine filtering.
+The appropriate coefficient set is chosen for each signal sample generated.
+
+The carrier is generated using the DDS method. Using 2 second order resonators,
+started in quadrature, might be more efficient, as it would have less impact on
+the processor cache than a table lookup approach. However, the DDS approach
+suits the receiver better, so then same signal generator is also used for the
+transmitter.
+*/
+
+#define V27TER_TX_FILTER_STEPS      9
+
+/*!
+    V.27ter modem transmit side descriptor. This defines the working state for a
+    single instance of a V.27ter modem transmitter.
+*/
+typedef struct
+{
+    /*! \brief The bit rate of the modem. Valid values are 2400 and 4800. */
+    int bit_rate;
+    /*! \brief The callback function used to get the next bit to be transmitted. */
+    get_bit_func_t get_bit;
+    /*! \brief A user specified opaque pointer passed to the callback function. */
+    void *user_data;
+
+    /*! \brief The gain factor needed to achieve the specified output power at 2400bps. */
+    float gain_2400;
+    /*! \brief The gain factor needed to achieve the specified output power at 4800bps. */
+    float gain_4800;
+
+    /*! \brief The route raised cosine (RRC) pulse shaping filter buffer. */
+    complexf_t rrc_filter[2*V27TER_TX_FILTER_STEPS];
+    /*! \brief Current offset into the RRC pulse shaping filter buffer. */
+    int rrc_filter_step;
+    
+    /*! \brief The register for the training and data scrambler. */
+    unsigned int scramble_reg;
+    /*! \brief A counter for the number of consecutive bits of repeating pattern through
+               the scrambler. */
+    int scrambler_pattern_count;
+    /*! \brief TRUE if transmitting the training sequence, or shutting down transmission.
+               FALSE if transmitting user data. */
+    int in_training;
+    /*! \brief A counter used to track progress through sending the training sequence. */
+    int training_step;
+
+    /*! \brief The current phase of the carrier (i.e. the DDS parameter). */
+    uint32_t carrier_phase;
+    /*! \brief The update rate for the phase of the carrier (i.e. the DDS increment). */
+    int32_t carrier_phase_rate;
+    /*! \brief The current fractional phase of the baud timing. */
+    int baud_phase;
+    /*! \brief The code number for the current position in the constellation. */
+    int constellation_state;
+    /*! \brief The get_bit function in use at any instant. */
+    get_bit_func_t current_get_bit;
+    /*! \brief Error and flow logging control */
+    logging_state_t logging;
+} v27ter_tx_state_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*! Adjust a V.27ter modem transmit context's power output.
+    \brief Adjust a V.27ter modem transmit context's output power.
+    \param s The modem context.
+    \param power The power level, in dBm0 */
+void v27ter_tx_power(v27ter_tx_state_t *s, float power);
+
+/*! Initialise a V.27ter modem transmit context.
+    \brief Initialise a V.27ter modem transmit context.
+    \param s The modem context.
+    \param rate The bit rate of the modem. Valid values are 2400 and 4800.
+    \param tep TRUE is the optional TEP tone is to be transmitted.
+    \param get_bit The callback routine used to get the data to be transmitted.
+    \param user_data An opaque pointer.
+    \return A pointer to the modem context, or NULL if there was a problem. */
+v27ter_tx_state_t *v27ter_tx_init(v27ter_tx_state_t *s, int rate, int tep, get_bit_func_t get_bit, void *user_data);
+
+/*! Reinitialise an existing V.27ter modem transmit context, so it may be reused.
+    \brief Reinitialise an existing V.27ter modem transmit context.
+    \param s The modem context.
+    \param rate The bit rate of the modem. Valid values are 2400 and 4800.
+    \param tep TRUE is the optional TEP tone is to be transmitted.
+    \return 0 for OK, -1 for bad parameter */
+int v27ter_tx_restart(v27ter_tx_state_t *s, int rate, int tep);
+
+/*! Release a V.27ter modem transmit context.
+    \brief Release a V.27ter modem transmit context.
+    \param s The modem context.
+    \return 0 for OK */
+int v27ter_tx_release(v27ter_tx_state_t *s);
+
+/*! Change the get_bit function associated with a V.27ter modem transmit context.
+    \brief Change the get_bit function associated with a V.27ter modem transmit context.
+    \param s The modem context.
+    \param get_bit The callback routine used to get the data to be transmitted.
+    \param user_data An opaque pointer. */
+void v27ter_tx_set_get_bit(v27ter_tx_state_t *s, get_bit_func_t get_bit, void *user_data);
+
+/*! Generate a block of V.27ter modem audio samples.
+    \brief Generate a block of V.27ter modem audio samples.
+    \param s The modem context.
+    \param amp The audio sample buffer.
+    \param len The number of samples to be generated.
+    \return The number of samples actually generated.
+*/
+int v27ter_tx(v27ter_tx_state_t *s, int16_t amp[], int len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/