spandsp 3.0.0
fsk.h
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1/*
2 * SpanDSP - a series of DSP components for telephony
3 *
4 * fsk.h - FSK modem transmit and receive parts
5 *
6 * Written by Steve Underwood <steveu@coppice.org>
7 *
8 * Copyright (C) 2003 Steve Underwood
9 *
10 * All rights reserved.
11 *
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Lesser General Public License version 2.1,
14 * as published by the Free Software Foundation.
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU Lesser General Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this program; if not, write to the Free Software
23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24 */
25
26/*! \file */
27
28/*! \page fsk_page FSK modems
29\section fsk_page_sec_1 What does it do?
30Most of the oldest telephony modems use incoherent FSK modulation. This module can
31be used to implement both the transmit and receive sides of a number of these
32modems. There are integrated definitions for:
33
34 - V.21
35 - V.23
36 - Bell 103
37 - Bell 202
38 - Weitbrecht (Used for TDD - Telecoms Device for the Deaf)
39
40The audio output or input is a stream of 16 bit samples, at 8000 samples/second.
41The transmit and receive sides can be used independantly.
42
43\section fsk_page_sec_2 The transmitter
44
45The FSK transmitter uses a DDS generator to synthesise the waveform. This
46naturally produces phase coherent transitions, as the phase update rate is
47switched, producing a clean spectrum. The symbols are not generally an integer
48number of samples long. However, the symbol time for the fastest data rate
49generally used (1200bps) is more than 7 samples long. The jitter resulting from
50switching at the nearest sample is, therefore, acceptable. No interpolation is
51used.
52
53\section fsk_page_sec_3 The receiver
54
55The FSK receiver uses a quadrature correlation technique to demodulate the
56signal. Two DDS quadrature oscillators are used. The incoming signal is
57correlated with the oscillator signals over a period of one symbol. The
58oscillator giving the highest net correlation from its I and Q outputs is the
59one that matches the frequency being transmitted during the correlation
60interval. Because the transmission is totally asynchronous, the demodulation
61process must run sample by sample to find the symbol transitions. The
62correlation is performed on a sliding window basis, so the computational load of
63demodulating sample by sample is not great.
64
65Three modes of symbol synchronisation are provided:
66
67 - In synchronous mode, symbol transitions are smoothed, to track their true
68 position in the prescence of high timing jitter. This provides the most
69 reliable symbol recovery in poor signal to noise conditions. However, it
70 takes a little time to settle, so it not really suitable for data streams
71 which must start up instantaneously (e.g. the TDD systems used by hearing
72 impaired people).
73
74 - In asynchronous mode each transition is taken at face value, with no temporal
75 smoothing. There is no settling time for this mode, but when the signal to
76 noise ratio is very poor it does not perform as well as the synchronous mode.
77
78 - In framed mode a soft decode of the bit stream occurs, which is more noise
79 tolerant than the asynchronous mode. This outputs fully decoded start-stop
80 framed characters, which have been parity checked. There is no option for
81 V.14 rate adaption, as this is not relevant for the truly asynchronous FSK
82 modems supported by this module.
83*/
84
85#if !defined(_SPANDSP_FSK_H_)
86#define _SPANDSP_FSK_H_
87
88/*!
89 FSK modem specification. This defines the frequencies, signal levels and
90 baud rate (== bit rate for simple FSK) for a single channel of an FSK modem.
91*/
92typedef struct
93{
94 /*! Short text name for the modem. */
95 const char *name;
96 /*! The frequency of the zero bit state, in Hz */
98 /*! The frequency of the one bit state, in Hz */
100 /*! The transmit power level, in dBm0 */
102 /*! The minimum acceptable receive power level, in dBm0 */
104 /*! The bit rate of the modem, in units of 1/100th bps */
106} fsk_spec_t;
107
108/* Predefined FSK modem channels */
109enum
110{
111 FSK_V21CH1 = 0,
112 FSK_V21CH2,
113 FSK_V23CH1,
114 FSK_V23CH2,
115 FSK_BELL103CH1,
116 FSK_BELL103CH2,
117 FSK_BELL202,
118 FSK_WEITBRECHT_4545, /* 45.45 baud version, used for TDD (Telecom Device for the Deaf) */
119 FSK_WEITBRECHT_50, /* 50 baud version, used for TDD (Telecom Device for the Deaf) */
120 FSK_WEITBRECHT_476, /* 47.6 baud version, used for V.18 probing */
121 FSK_V21CH1_110 /* 110 bps version of V.21 channel 1, as used by V.18 */
122};
123
124enum
125{
126 FSK_FRAME_MODE_ASYNC = 0,
127 FSK_FRAME_MODE_SYNC = 1,
128 FSK_FRAME_MODE_FRAMED = 2
129};
130
131SPAN_DECLARE_DATA extern const fsk_spec_t preset_fsk_specs[];
132
133/*!
134 FSK modem transmit descriptor. This defines the state of a single working
135 instance of an FSK modem transmitter.
136*/
138
139/* The longest window will probably be 106 for 75 baud */
140#define FSK_MAX_WINDOW_LEN 128
141
142/*!
143 FSK modem receive descriptor. This defines the state of a single working
144 instance of an FSK modem receiver.
145*/
147
148#if defined(__cplusplus)
149extern "C"
150{
151#endif
152
153/*! Initialise an FSK modem transmit context.
154 \brief Initialise an FSK modem transmit context.
155 \param s The modem context.
156 \param spec The specification of the modem tones and rate.
157 \param get_bit The callback routine used to get the data to be transmitted.
158 \param user_data An opaque pointer.
159 \return A pointer to the modem context, or NULL if there was a problem. */
160SPAN_DECLARE(fsk_tx_state_t *) fsk_tx_init(fsk_tx_state_t *s,
161 const fsk_spec_t *spec,
162 span_get_bit_func_t get_bit,
163 void *user_data);
164
165SPAN_DECLARE(int) fsk_tx_restart(fsk_tx_state_t *s, const fsk_spec_t *spec);
166
167SPAN_DECLARE(int) fsk_tx_release(fsk_tx_state_t *s);
168
169SPAN_DECLARE(int) fsk_tx_free(fsk_tx_state_t *s);
170
171/*! Adjust an FSK modem transmit context's power output.
172 \brief Adjust an FSK modem transmit context's power output.
173 \param s The modem context.
174 \param power The power level, in dBm0 */
175SPAN_DECLARE(void) fsk_tx_power(fsk_tx_state_t *s, float power);
176
177SPAN_DECLARE(void) fsk_tx_set_get_bit(fsk_tx_state_t *s, span_get_bit_func_t get_bit, void *user_data);
178
179/*! Change the modem status report function associated with an FSK modem transmit context.
180 \brief Change the modem status report function associated with an FSK modem transmit context.
181 \param s The modem context.
182 \param handler The callback routine used to report modem status changes.
183 \param user_data An opaque pointer. */
184SPAN_DECLARE(void) fsk_tx_set_modem_status_handler(fsk_tx_state_t *s, span_modem_status_func_t handler, void *user_data);
185
186/*! Generate a block of FSK modem audio samples.
187 \brief Generate a block of FSK modem audio samples.
188 \param s The modem context.
189 \param amp The audio sample buffer.
190 \param len The number of samples to be generated.
191 \return The number of samples actually generated.
192*/
193SPAN_DECLARE(int) fsk_tx(fsk_tx_state_t *s, int16_t amp[], int len);
194
195/*! Get the current received signal power.
196 \param s The modem context.
197 \return The signal power, in dBm0. */
198SPAN_DECLARE(float) fsk_rx_signal_power(fsk_rx_state_t *s);
199
200/*! Adjust an FSK modem receive context's carrier detect power threshold.
201 \brief Adjust an FSK modem receive context's carrier detect power threshold.
202 \param s The modem context.
203 \param cutoff The power level, in dBm0 */
204SPAN_DECLARE(void) fsk_rx_set_signal_cutoff(fsk_rx_state_t *s, float cutoff);
205
206/*! Set the framing parameters for a an FSK modem receive context in
207 FSK_FRAME_MODE_FRAMED mode.
208 \brief Set the framing parameters.
209 \param s The modem context.
210 \param data_bits;
211 \param parity;
212 \param stop_bits; */
213SPAN_DECLARE(void) fsk_rx_set_frame_parameters(fsk_rx_state_t *s,
214 int data_bits,
215 int parity,
216 int stop_bits);
217
218SPAN_DECLARE(int) fsk_rx_get_parity_errors(fsk_rx_state_t *s, bool reset);
219
220SPAN_DECLARE(int) fsk_rx_get_framing_errors(fsk_rx_state_t *s, bool reset);
221
222/*! Initialise an FSK modem receive context.
223 \brief Initialise an FSK modem receive context.
224 \param s The modem context.
225 \param spec The specification of the modem tones and rate.
226 \param framing_mode
227 \param put_bit The callback routine used to put the received data.
228 \param user_data An opaque pointer.
229 \return A pointer to the modem context, or NULL if there was a problem. */
230SPAN_DECLARE(fsk_rx_state_t *) fsk_rx_init(fsk_rx_state_t *s,
231 const fsk_spec_t *spec,
232 int framing_mode,
233 span_put_bit_func_t put_bit,
234 void *user_data);
235
236SPAN_DECLARE(int) fsk_rx_restart(fsk_rx_state_t *s,
237 const fsk_spec_t *spec,
238 int framing_mode);
239
240SPAN_DECLARE(int) fsk_rx_release(fsk_rx_state_t *s);
241
242SPAN_DECLARE(int) fsk_rx_free(fsk_rx_state_t *s);
243
244/*! Process a block of received FSK modem audio samples.
245 \brief Process a block of received FSK modem audio samples.
246 \param s The modem context.
247 \param amp The audio sample buffer.
248 \param len The number of samples in the buffer.
249 \return The number of samples unprocessed.
250*/
251SPAN_DECLARE(int) fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len);
252
253/*! Fake processing of a missing block of received FSK modem audio samples
254 (e.g due to packet loss).
255 \brief Fake processing of a missing block of received FSK modem audio samples.
256 \param s The modem context.
257 \param len The number of samples to fake.
258 \return The number of samples unprocessed.
259*/
260SPAN_DECLARE(int) fsk_rx_fillin(fsk_rx_state_t *s, int len);
261
262SPAN_DECLARE(void) fsk_rx_set_put_bit(fsk_rx_state_t *s, span_put_bit_func_t put_bit, void *user_data);
263
264/*! Change the modem status report function associated with an FSK modem receive context.
265 \brief Change the modem status report function associated with an FSK modem receive context.
266 \param s The modem context.
267 \param handler The callback routine used to report modem status changes.
268 \param user_data An opaque pointer. */
269SPAN_DECLARE(void) fsk_rx_set_modem_status_handler(fsk_rx_state_t *s, span_modem_status_func_t handler, void *user_data);
270
271#if defined(__cplusplus)
272}
273#endif
274
275#endif
276/*- End of file ------------------------------------------------------------*/
int(* span_get_bit_func_t)(void *user_data)
Definition async.h:127
void(* span_modem_status_func_t)(void *user_data, int status)
Definition async.h:131
void(* span_put_bit_func_t)(void *user_data, int bit)
Definition async.h:123
void fsk_rx_set_signal_cutoff(fsk_rx_state_t *s, float cutoff)
Adjust an FSK modem receive context's carrier detect power threshold.
Definition fsk.c:271
void fsk_rx_set_frame_parameters(fsk_rx_state_t *s, int data_bits, int parity, int stop_bits)
Set the framing parameters.
Definition fsk.c:300
int fsk_tx(fsk_tx_state_t *s, int16_t amp[], int len)
Generate a block of FSK modem audio samples.
Definition fsk.c:162
struct fsk_rx_state_s fsk_rx_state_t
Definition fsk.h:146
int fsk_rx_fillin(fsk_rx_state_t *s, int len)
Fake processing of a missing block of received FSK modem audio samples.
Definition fsk.c:637
fsk_tx_state_t * fsk_tx_init(fsk_tx_state_t *s, const fsk_spec_t *spec, span_get_bit_func_t get_bit, void *user_data)
Initialise an FSK modem transmit context.
Definition fsk.c:237
void fsk_tx_set_modem_status_handler(fsk_tx_state_t *s, span_modem_status_func_t handler, void *user_data)
Change the modem status report function associated with an FSK modem transmit context.
Definition fsk.c:214
float fsk_rx_signal_power(fsk_rx_state_t *s)
Definition fsk.c:280
int fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len)
Process a block of received FSK modem audio samples.
Definition fsk.c:396
void fsk_rx_set_modem_status_handler(fsk_rx_state_t *s, span_modem_status_func_t handler, void *user_data)
Change the modem status report function associated with an FSK modem receive context.
Definition fsk.c:293
struct fsk_tx_state_s fsk_tx_state_t
Definition fsk.h:137
void fsk_tx_power(fsk_tx_state_t *s, float power)
Adjust an FSK modem transmit context's power output.
Definition fsk.c:201
fsk_rx_state_t * fsk_rx_init(fsk_rx_state_t *s, const fsk_spec_t *spec, int framing_mode, span_put_bit_func_t put_bit, void *user_data)
Initialise an FSK modem receive context.
Definition fsk.c:725
Definition private/fsk.h:59
int framing_mode
Synchronous/asynchronous/framed control.
Definition private/fsk.h:62
Definition fsk.h:93
int freq_one
Definition fsk.h:99
const char * name
Definition fsk.h:95
int tx_level
Definition fsk.h:101
int min_level
Definition fsk.h:103
int baud_rate
Definition fsk.h:105
int freq_zero
Definition fsk.h:97
Definition private/fsk.h:34