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audio.c
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/*
* Copyright (c) 2020-21, Kalopa Robotics Limited. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials provided
* with the distribution.
*
* 3. Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT
* NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
* FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
* SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
* GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* ABSTRACT
* This code handles the actual operation of creating a tone (or silence)
* for morse output. It relies heavily on the ALSA sound library for the
* dirty work of getting audio out.
*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <math.h>
#include "libmorse.h"
/*
* Generate a sinusoidal tone at the desired frequency. We use a small curve
* at the end of the wave form to avoid clicks. The maths here might not be
* perfect...
*/
void
morse_audio_tone(struct morse *mp, int len)
{
int i, fade = 0;
double value, theta;
fade = mp->sample_rate / 440;
for (i = 0; i < len; i++) {
if (i > (len - fade)) {
/*
* Need to decay the last 100 or so samples to avoid clicking.
*/
theta = (double )(i - len + fade) * M_PI_2 / (double )fade;
value = (1 - sin(theta)) * (double )mp->word;
} else
value = (double )mp->word;
theta = (2.0 * M_PI * (double )i * (double )mp->tone_frequency / mp->sample_rate);
sound_out(mp, (int )(value * sin(theta) + 0.5));
}
}
/*
* Add a block of silence. Note that it is the larger of the element delay,
* the character delay, and the word delay. Whichever was last.
*/
void
morse_audio_silence(struct morse *mp)
{
while (mp->sym_delay > 0) {
sound_out(mp, 0);
mp->sym_delay--;
}
}
/*
* Return the time stamp in seconds. Simply the number of values transmitted
* divided by the samples per second.
*/
double
morse_timestamp(struct morse *mp)
{
return((double )mp->time_stamp / (double )mp->sample_rate);
}