tinyplay扩展-播放自制正弦波

存在意义

tinyplay常用于音频测试，一般是通过播放wav文件来测试开发板音频模块是否有问题，但是wav是没有经过压缩的文件，所以会占用较多内存，对于一些内存较小的开发板我们可以通过反复播放一段正弦波来测试音频模块

思路设计

简单的说就是通过C标准库提供的sin函数生成波形的采样点，然后将数据填充到buffer，再写一个循环反复写入PCM设备即可

重点难点

1. 想要实现这个功能必须对tinyplay的播放流程有大致的了解（用户层即可）

2. 理清楚采样频率a、采样点数b和正弦波频率c的关系：波形在一个周期内的b=a/c，也就是说我们可以通过控制a和b来播放特定频率的正弦波。这里补充一点，人耳能听到的声音频率为20Hz到20KHz，但是一般人能发出的声音频率就是几十到一千赫兹，所以声波频率设置成该频率听起来比较舒适

3. 正弦波的振幅一般调到最大便于测试，而最大值则是根据传入的样本长度参数确定（16、24、32）

4. 既然是反复写入同一段数据到PCM那么，填充buffer时注意前后边缘不能出现数据断层（最好就是一个周期：从零开始到0结束），不然播放时声音会不丝滑

源码

/* tinyplay.c
**
** Copyright 2011, The Android Open Source Project
**
** Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are met:
**     * Redistributions of source code must retain the above copyright
**       notice, this list of conditions and the following disclaimer.
**     * 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.
**     * Neither the name of The Android Open Source Project 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 Android Open Source Project ``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 Android Open Source Project 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.
*/#include <tinyalsa/asoundlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <signal.h>
#include <endian.h>
#include <time.h>
#include <math.h>#define ID_RIFF 0x46464952
#define ID_WAVE 0x45564157
#define ID_FMT  0x20746d66
#define ID_DATA 0x61746164struct riff_wave_header {uint32_t riff_id;uint32_t riff_sz;uint32_t wave_id;
};struct chunk_header {uint32_t id;uint32_t sz;
};struct chunk_fmt {uint16_t audio_format;uint16_t num_channels;uint32_t sample_rate;uint32_t byte_rate;uint16_t block_align;uint16_t bits_per_sample;
};static int close = 0;void display_progress(float len, float all_len);
void play_sample(unsigned int card, unsigned int device, unsigned int channels,unsigned int rate, unsigned int bits, unsigned int period_size,unsigned int period_count);void stream_close(int sig)
{/* allow the stream to be closed gracefully */signal(sig, SIG_IGN);close = 1;
}int main(int argc, char **argv)
{unsigned int device = 0;unsigned int card = 0;unsigned int period_size = 1000;unsigned int period_count = 4;unsigned int channels = 1;unsigned int rate = 44100;unsigned int bits = 16;if(argc < 2) {fprintf(stderr, "Usage: %s file.wav [-D card] [-d device] [-p period_size]"" [-n n_periods] [-b bits] [-v vol]\n", argv[0]);}/* parse command line arguments */argv += 2;while (*argv) {if (strcmp(*argv, "-d") == 0) {argv++;if (*argv)device = atoi(*argv);}if (strcmp(*argv, "-p") == 0) {argv++;if (*argv)period_size = atoi(*argv);}if (strcmp(*argv, "-n") == 0) {argv++;if (*argv)period_count = atoi(*argv);}if (strcmp(*argv, "-c") == 0) {argv++;if (*argv)channels = atoi(*argv);}if (strcmp(*argv, "-b") == 0) {argv++;if (*argv)bits = atoi(*argv);}if (strcmp(*argv, "-D") == 0) {argv++;if (*argv)card = atoi(*argv);}if (*argv)argv++; }play_sample(card, device, channels, rate, bits, period_size, period_count);return 0;
}int check_param(struct pcm_params *params, unsigned int param, unsigned int value,char *param_name, char *param_unit)
{unsigned int min;unsigned int max;int is_within_bounds = 1;min = pcm_params_get_min(params, param);if (value < min) {fprintf(stderr, "%s is %u%s, device only supports >= %u%s\n", param_name, value,param_unit, min, param_unit);is_within_bounds = 0;}max = pcm_params_get_max(params, param);if (value > max) {fprintf(stderr, "%s is %u%s, device only supports <= %u%s\n", param_name, value,param_unit, max, param_unit);is_within_bounds = 0;}return is_within_bounds;
}int sample_is_playable(unsigned int card, unsigned int device, unsigned int channels,unsigned int rate, unsigned int bits, unsigned int period_size,unsigned int period_count)
{struct pcm_params *params;int can_play;params = pcm_params_get(card, device, PCM_OUT);if (params == NULL) {fprintf(stderr, "Unable to open PCM device %u.\n", device);return 0;}can_play = check_param(params, PCM_PARAM_RATE, rate, "Sample rate", "Hz");can_play &= check_param(params, PCM_PARAM_CHANNELS, channels, "Sample", " channels");can_play &= check_param(params, PCM_PARAM_SAMPLE_BITS, bits, "Bitrate", " bits");can_play &= check_param(params, PCM_PARAM_PERIOD_SIZE, period_size, "Period size", " frames");can_play &= check_param(params, PCM_PARAM_PERIODS, period_count, "Period count", " periods");pcm_params_free(params);return can_play;
}void play_sample(unsigned int card, unsigned int device, unsigned int channels,unsigned int rate, unsigned int bits, unsigned int period_size,unsigned int period_count)
{struct pcm_config config;struct pcm *pcm;uint16_t *buffer;unsigned int size;unsigned int i;unsigned int points = 100;   /* 采样点数 */memset(&config, 0, sizeof(config));config.channels = channels;config.rate = rate;config.period_size = period_size;config.period_count = period_count;if (bits == 32)config.format = PCM_FORMAT_S32_LE;else if (bits == 24)config.format = PCM_FORMAT_S24_3LE;else if (bits == 16)config.format = PCM_FORMAT_S16_LE;config.start_threshold = 0;config.stop_threshold = 0;config.silence_threshold = 0;if (!sample_is_playable(card, device, channels, rate, bits, period_size, period_count)) {return;}pcm = pcm_open(card, device, PCM_OUT, &config);if (!pcm || !pcm_is_ready(pcm)) {fprintf(stderr, "Unable to open PCM device %u (%s)\n",device, pcm_get_error(pcm));return;}size = pcm_frames_to_bytes(pcm, pcm_get_buffer_size(pcm));buffer = malloc(size);if (!buffer) {fprintf(stderr, "Unable to allocate %d bytes\n", size);printf("3\n");free(buffer);pcm_close(pcm);return;}/* f = rate / points */for(i = 0; i < size / 2; i ++){buffer[i] = 32768 * sin(2 * 3.14159 / points * (i % points)) + 32768;}printf("Playing sample: %u ch, %u hz, %u bit\n", channels, rate, bits);/* catch ctrl-c to shutdown cleanly */signal(SIGINT, stream_close);do {pcm_write(pcm, buffer, size);} while (!close);printf("\n");free(buffer);pcm_close(pcm);
}

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tinyplay扩展-播放自制正弦波

存在意义

思路设计

重点难点

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