Android Tinyalsa

一 、tinyalsa简介

ALSA全称是Advanced Linux Sound Architecture，是Linux内核2.6后续版本中支持音频系统的标准接口程序，由ALSA库、内核驱动和相关测 试开发工具组成。tinyalsa是一个用来和内核交互的接口库。在aosp的/external/tinyalsa/下可以看到相关的应用。

二、相关模块及功能

1. 驱动部分
   Android中，查看/dev/snd下面节点：

ls -l /dev/snd/
total 0
crw-rw---- 1 system audio 116,   0 2023-07-17 17:26:28.290000000 +0800 controlC0
crw-rw---- 1 system audio 116,  24 2023-07-17 17:26:28.290000000 +0800 pcmC0D0c
crw-rw---- 1 system audio 116,  16 2023-07-17 17:26:28.290000000 +0800 pcmC0D0p
crw-rw---- 1 system audio 116,  33 2023-07-17 17:26:28.300000000 +0800 timer

其中/dev/snd/controlC%u，一般是C0表示音频控制设备文件，例如通道选择、混音、麦克风控制等。pcm设备中的格式/dev/snd/pcmC%uD%u%p,C代表card,D代表device,c代表capture,p代表playback。timer：定时器。

2. 音频工具

tinycap.c ： 设备采集pcm格式的码流，并保存为wav格式的文件。

tinymix.c ： pcm设备的控制，可得到音频通路相关的配置参数。

tinypcminfo.c：查看pcm设备具备什么能力。

tinyplay.c：pcm播放wav格式的音频文件。

3. goldfish中hal的实现

/device/generic/goldfish/audio/

//定义
struct audio_module HAL_MODULE_INFO_SYM = {
    .common = {
        .tag = HARDWARE_MODULE_TAG,
        .module_api_version = AUDIO_MODULE_API_VERSION_0_1,
        .hal_api_version = HARDWARE_HAL_API_VERSION,
        .id = AUDIO_HARDWARE_MODULE_ID,
        .name = "Generic audio HW HAL",
        .author = "The Android Open Source Project",
        .methods = &hal_module_methods,
    },
//打开实现
static struct hw_module_methods_t hal_module_methods = {
    .open = adev_open,
};

4. 工具使用

/data/local/tmp # ./tinymix                                                                   
Mixer name: 'HDA Intel'
Number of controls: 8
ctl type num name                                     value

0 INT 2 Master Playback Volume                   74 74
1 BOOL 2 Master Playback Switch                   On On
2 INT 2 Capture Volume                           74 74
3 BOOL 2 Capture Switch                           On On
4 BOOL 1 Line Phantom Jack                        On
5 BOOL 1 Line Out Phantom Jack                    On
6 INT 2 Playback Channel Map                     3 4
7 INT 2 Capture Channel Map                      0 0

录音：

 /data/local/tmp #./tinycap
Usage: ./tinycap file.wav [-D card] [-d device] [-c channels] [-r rate] [-b bits] [-p period_size] [-n n_periods] [-T capture time]

播放：

/data/local/tmp # ./tinyplay
Usage: ./tinyplay file.wav [-D card] [-d device] [-p period_size] [-n n_periods]

5. 相关代码

goldfish 中hal层入口：

static int adev_open(const hw_module_t* module, const char* name,
                     hw_device_t** device)
{
    ....
    adev = calloc(1, sizeof(struct generic_audio_device));

    pthread_mutex_init(&adev->lock, (const pthread_mutexattr_t *) NULL);
    ....
    //注册函数
    adev->device.common.tag = HARDWARE_DEVICE_TAG;
    adev->device.common.version = AUDIO_DEVICE_API_VERSION_2_0;
    adev->device.common.module = (struct hw_module_t *) module;
    adev->device.common.close = adev_close;

    adev->device.init_check = adev_init_check;               // no op
    adev->device.set_voice_volume = adev_set_voice_volume;   // no op
    adev->device.set_master_volume = adev_set_master_volume; // no op
    adev->device.get_master_volume = adev_get_master_volume; // no op
    adev->device.set_master_mute = adev_set_master_mute;     // no op
    adev->device.get_master_mute = adev_get_master_mute;     // no op
    adev->device.set_mode = adev_set_mode;                   // no op
    adev->device.set_mic_mute = adev_set_mic_mute;
    adev->device.get_mic_mute = adev_get_mic_mute;
    adev->device.set_parameters = adev_set_parameters;       // no op
    adev->device.get_parameters = adev_get_parameters;       // no op
    adev->device.get_input_buffer_size = adev_get_input_buffer_size;
    adev->device.open_output_stream = adev_open_output_stream;
    adev->device.close_output_stream = adev_close_output_stream;
    adev->device.open_input_stream = adev_open_input_stream;
    adev->device.close_input_stream = adev_close_input_stream;
    adev->device.dump = adev_dump;

    *device = &adev->device.common;

    //PCM_CARD =0 调用tinyalsa的mixer_open函数
    adev->mixer = mixer_open(PCM_CARD);

    struct mixer_ctl *ctl;
    ......
}

mixer_open是tinyalsa提供的api,打开为/dev/snd/controlC%u.

struct mixer *mixer_open(unsigned int card)
{
    struct snd_ctl_elem_list elist;
    struct snd_ctl_elem_id *eid = NULL;
    struct mixer *mixer = NULL;
    unsigned int n;
    int fd;
    char fn[256];

    snprintf(fn, sizeof(fn), "/dev/snd/controlC%u", card);
    fd = open(fn, O_RDWR);
    if (fd < 0)
        return 0;
    ....
    free(eid);
    return mixer;

fail:
    /* TODO: verify frees in failure case */
    if (eid)
        free(eid);
    if (mixer)
        mixer_close(mixer);
    else if (fd >= 0)
        close(fd);
    return 0;
}

录音代码：

#include <tinyalsa/asoundlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <signal.h>
#include <string.h>
#include <time.h>

#define ID_RIFF 0x46464952
#define ID_WAVE 0x45564157
#define ID_FMT  0x20746d66
#define ID_DATA 0x61746164

#define FORMAT_PCM 1

struct wav_header {
    uint32_t riff_id;
    uint32_t riff_sz;
    uint32_t riff_fmt;
    uint32_t fmt_id;
    uint32_t fmt_sz;
    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;
    uint32_t data_id;
    uint32_t data_sz;
};

int capturing = 1;

unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device,
                            unsigned int channels, unsigned int rate,
                            enum pcm_format format, unsigned int period_size,
                            unsigned int period_count, unsigned int cap_time);

void sigint_handler(int sig __unused)
{
    capturing = 0;
}

int main(int argc, char **argv)
{
    FILE *file;
    struct wav_header header;
    unsigned int card = 0;
    unsigned int device = 0;
    unsigned int channels = 2;
    unsigned int rate = 44100;
    unsigned int bits = 16;
    unsigned int frames;
    unsigned int period_size = 1024;
    unsigned int period_count = 4;
    unsigned int cap_time = 0;
    enum pcm_format format;

    if (argc < 2) {
        fprintf(stderr, "Usage: %s file.wav [-D card] [-d device]"
                " [-c channels] [-r rate] [-b bits] [-p period_size]"
                " [-n n_periods] [-T capture time]\n", argv[0]);
        return 1;
    }

    file = fopen(argv[1], "wb");
    if (!file) {
        fprintf(stderr, "Unable to create file '%s'\n", argv[1]);
        return 1;
    }

    /* parse command line arguments */
    argv += 2;
    while (*argv) {
        if (strcmp(*argv, "-d") == 0) {
            argv++;
            if (*argv)
                device = atoi(*argv);
        } else if (strcmp(*argv, "-c") == 0) {
            argv++;
            if (*argv)
                channels = atoi(*argv);
        } else if (strcmp(*argv, "-r") == 0) {
            argv++;
            if (*argv)
                rate = atoi(*argv);
        } else if (strcmp(*argv, "-b") == 0) {
            argv++;
            if (*argv)
                bits = atoi(*argv);
        } else if (strcmp(*argv, "-D") == 0) {
            argv++;
            if (*argv)
                card = atoi(*argv);
        } else if (strcmp(*argv, "-p") == 0) {
            argv++;
            if (*argv)
                period_size = atoi(*argv);
        } else if (strcmp(*argv, "-n") == 0) {
            argv++;
            if (*argv)
                period_count = atoi(*argv);
        } else if (strcmp(*argv, "-T") == 0) {
            argv++;
            if (*argv)
                cap_time = atoi(*argv);
        }
        if (*argv)
            argv++;
    }

    header.riff_id = ID_RIFF;
    header.riff_sz = 0;
    header.riff_fmt = ID_WAVE;
    header.fmt_id = ID_FMT;
    header.fmt_sz = 16;
    header.audio_format = FORMAT_PCM;
    header.num_channels = channels;
    header.sample_rate = rate;

    switch (bits) {
    case 32:
        format = PCM_FORMAT_S32_LE;
        break;
    case 24:
        format = PCM_FORMAT_S24_LE;
        break;
    case 16:
        format = PCM_FORMAT_S16_LE;
        break;
    default:
        fprintf(stderr, "%u bits is not supported.\n", bits);
        fclose(file);
        return 1;
    }

    header.bits_per_sample = pcm_format_to_bits(format);
    header.byte_rate = (header.bits_per_sample / 8) * channels * rate;
    header.block_align = channels * (header.bits_per_sample / 8);
    header.data_id = ID_DATA;

    /* leave enough room for header */
    fseek(file, sizeof(struct wav_header), SEEK_SET);

    /* install signal handler and begin capturing */
    signal(SIGINT, sigint_handler);
    signal(SIGHUP, sigint_handler);
    signal(SIGTERM, sigint_handler);
    frames = capture_sample(file, card, device, header.num_channels,
                            header.sample_rate, format,
                            period_size, period_count, cap_time);
    printf("Captured %u frames\n", frames);

    /* write header now all information is known */
    header.data_sz = frames * header.block_align;
    header.riff_sz = header.data_sz + sizeof(header) - 8;
    fseek(file, 0, SEEK_SET);
    fwrite(&header, sizeof(struct wav_header), 1, file);

    fclose(file);

    return 0;
}

unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device,
                            unsigned int channels, unsigned int rate,
                            enum pcm_format format, unsigned int period_size,
                            unsigned int period_count, unsigned int cap_time)
{
    struct pcm_config config;
    struct pcm *pcm;
    char *buffer;
    unsigned int size;
    unsigned int bytes_read = 0;
    unsigned int frames = 0;
    struct timespec end;
    struct timespec now;

    memset(&config, 0, sizeof(config));
    config.channels = channels;
    config.rate = rate;
    config.period_size = period_size;
    config.period_count = period_count;
    config.format = format;
    config.start_threshold = 0;
    config.stop_threshold = 0;
    config.silence_threshold = 0;

    pcm = pcm_open(card, device, PCM_IN, &config);
    if (!pcm || !pcm_is_ready(pcm)) {
        fprintf(stderr, "Unable to open PCM device (%s)\n",
                pcm_get_error(pcm));
        return 0;
    }

    size = pcm_frames_to_bytes(pcm, pcm_get_buffer_size(pcm));
    buffer = malloc(size);
    if (!buffer) {
        fprintf(stderr, "Unable to allocate %u bytes\n", size);
        free(buffer);
        pcm_close(pcm);
        return 0;
    }

    printf("Capturing sample: %u ch, %u hz, %u bit\n", channels, rate,
           pcm_format_to_bits(format));

    clock_gettime(CLOCK_MONOTONIC, &now);
    end.tv_sec = now.tv_sec + cap_time;
    end.tv_nsec = now.tv_nsec;

    while (capturing && !pcm_read(pcm, buffer, size)) {
        if (fwrite(buffer, 1, size, file) != size) {
            fprintf(stderr,"Error capturing sample\n");
            break;
        }
        bytes_read += size;
        if (cap_time) {
            clock_gettime(CLOCK_MONOTONIC, &now);
            if (now.tv_sec > end.tv_sec ||
                (now.tv_sec == end.tv_sec && now.tv_nsec >= end.tv_nsec))
                break;
        }
    }

    frames = pcm_bytes_to_frames(pcm, bytes_read);
    free(buffer);
    pcm_close(pcm);
    return frames;
}

三、参考链接

其他平台 tinyalsa

ALSA应用开发