--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.6pre17/src/spandsp/v27ter_tx.h	Fri Jun 25 15:50:58 2010 +0200
@@ -0,0 +1,148 @@
+/*
+ * 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 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: v27ter_tx.h,v 1.43 2009/07/09 13:52:09 steveu Exp $
+ */
+
+/*! \file */
+
+#if !defined(_SPANDSP_V27TER_TX_H_)
+#define _SPANDSP_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.
+*/
+
+/*!
+    V.27ter modem transmit side descriptor. This defines the working state for a
+    single instance of a V.27ter modem transmitter.
+*/
+typedef struct v27ter_tx_state_s v27ter_tx_state_t;
+
+#if defined(__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 */
+SPAN_DECLARE(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 bit_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. */
+SPAN_DECLARE(v27ter_tx_state_t *) v27ter_tx_init(v27ter_tx_state_t *s, int bit_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 bit_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 */
+SPAN_DECLARE(int) v27ter_tx_restart(v27ter_tx_state_t *s, int bit_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 */
+SPAN_DECLARE(int) v27ter_tx_release(v27ter_tx_state_t *s);
+
+/*! Free a V.27ter modem transmit context.
+    \brief Free a V.27ter modem transmit context.
+    \param s The modem context.
+    \return 0 for OK */
+SPAN_DECLARE(int) v27ter_tx_free(v27ter_tx_state_t *s);
+
+/*! Get the logging context associated with a V.27ter modem transmit context.
+    \brief Get the logging context associated with a V.27ter modem transmit context.
+    \param s The modem context.
+    \return A pointer to the logging context */
+SPAN_DECLARE(logging_state_t *) v27ter_tx_get_logging_state(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. */
+SPAN_DECLARE(void) v27ter_tx_set_get_bit(v27ter_tx_state_t *s, get_bit_func_t get_bit, void *user_data);
+
+/*! Change the modem status report function associated with a V.27ter modem transmit context.
+    \brief Change the modem status report function associated with a V.27ter modem transmit context.
+    \param s The modem context.
+    \param handler The callback routine used to report modem status changes.
+    \param user_data An opaque pointer. */
+SPAN_DECLARE(void) v27ter_tx_set_modem_status_handler(v27ter_tx_state_t *s, modem_tx_status_func_t handler, 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.
+*/
+SPAN_DECLARE_NONSTD(int) v27ter_tx(v27ter_tx_state_t *s, int16_t amp[], int len);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/