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#ifndef _TONE_H
#define _TONE_H
/*!
* Fixed-point tone generator.
*
* The code here implements a simple fixed-point tone generator that uses
* integer arithmetic to generate a sinusoid at a fixed sample rate of
* 16kHz.
*
* To set the initial state of the state machine, you specify a frequency
* and duration using tone_reset. The corresponding C file embeds a
* sinusoid look-up table. The total number of samples is computed for
* the given time and used to initialise 'remain', 'time' is initialised
* to 0, and 'step' gives the amount to increment 'time' by each iteration.
*
* The samples are retrieved by repeatedly calling tone_next. This
* advances 'time' and decrements 'remain'. The tone is complete when
* 'remain' is zero.
*
* Author Stuart Longland <[email protected]>
* Copyright (C) 2015 FreeDV project.
*
* 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 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, see
* <http://www.gnu.org/licenses/>.
*/
#include <stdint.h>
/*! Tone sampling rate in Hz. */
#define TONE_FS 16000
/*!
* Tone generator state. This holds the current state of the tone
* generator in order to decide what sample to release next.
*/
struct tone_gen_t {
/*! Current sample. (Q12) */
uint32_t sample;
/*!
* Time remaining in samples. (integer) Playback is finished
* when this reaches zero.
*/
uint16_t remain;
/*!
* Subsample step (Q12). This is the number of samples (or part
* thereof) to advance "sample". Special case: when zero, sample
* is not advanced, silence is generated instead.
*/
uint16_t step;
};
/*!
* Re-set the tone generator.
*
* @param tone_gen Tone generator to reset.
* @param freq Frequency in Hz, 0 = silence.
* @param duration Duration in milliseconds. 0 to stop.
*/
void tone_reset(
struct tone_gen_t* const tone_gen,
uint16_t freq, uint16_t duration);
/*!
* Retrieve the next sample from the tone generator.
* @param tone_gen Tone generator to update.
*/
int16_t tone_next(
struct tone_gen_t* const tone_gen);
/*!
* Retrieve the current time in milliseconds.
*/
uint32_t tone_msec(const struct tone_gen_t* const tone_gen);
#endif
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