Audio:Android-TinyAlsa架构 Mixer API

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于 2021-12-13 11:03:23 首次发布

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本文深入探讨了Android音频框架中TinyAlsa库的mixer配置，重点分析了tinymix工具的源码，包括tinymix_open、tinymix_list_controls、tinymix_detail_control和tinymix_set_value等关键方法。tinymix用于查看和设置音频通道参数，tinymix_list_controls列出所有混音器控制，tinymix_detail_control展示控制详情，tinymix_set_value则用于修改控制值。这些接口在Android音频设备初始化和配置中起到关键作用。

Android中对音频多声道数据的配置binary tinymix是tinyplay执行前必要的步骤，对tinymix的源码进行check在整合tinyalsa相关通道配置以及流程上是非常有必要的。tinymix梳理之后还是比较简单的，主要有mixer_open, mixer_close, tinymix_list_controls, tinymix_detail_control, tinymix_set_value这个几个方法。

1.tinymix.c

file path: external/tinyalsa/tinymix.c

int main(int argc, char **argv)
{
    struct mixer *mixer;
    int card = 0;
    int ret = 0;

    while (1) {
        int option_index = 0;
        int option_char = 0;

        option_char = getopt_long(argc, argv, tinymix_short_options,
                                  tinymix_long_options, &option_index);
        if (option_char == -1)
            break;

        switch (option_char) {
        case 'D':
            ...
    }


    //mixer_open打开对应card的mixer配置，默认为0
    mixer = mixer_open(card);
    if (!mixer) {
        fprintf(stderr, "Failed to open mixer\n");
        return ENODEV;
    }

    if (argc == optind) {
        printf("Mixer name: '%s'\n", mixer_get_name(mixer));
        //查看所有的mixer配置参数
        tinymix_list_controls(mixer);
    } else if (argc == optind + 1) {
        //查看某一项mixer配置参数
        ret = tinymix_detail_control(mixer, argv[optind], !g_value_only, !g_value_only);
    } else if (argc >= optind + 2) {
        //通过mixer设置通道参数
        ret = tinymix_set_value(mixer, argv[optind], &argv[optind + 1], argc - optind - 1);
    }

    //最后通过mixer_close关闭mixer配置
    mixer_close(mixer);

    return ret;
}

2.tinytest.c

参考tinymix.c写入相关的音频配置参数S_NORMAL_AP01_C_CODEC SWITCH 和 S_VOICE_C_CODEC SWITCH都写为1，on的状态。

int main(int argc, char **argv)
{
    struct mixer *mixer;
    int card = 0;
    int i;
    char *control1 = "S_NORMAL_AP01_C_CODEC SWITCH";
    char *control2 = "S_VOICE_C_CODEC SWITCH";
    char *values = "1";

    if ((argc > 2) && (strcmp(argv[1], "-D") == 0)) {
        argv++;
        if (argv[1]) {
            card = atoi(argv[1]);
            argv++;
            argc -= 2;
        } else {
            argc -= 1;
        }
    }

    mixer = mixer_open(card);
    if (!mixer) {
        DEBUG_Log_Err("Failed to open mixer\n");
        return EXIT_FAILURE;
    }

    DEBUG_Log_Info("shengjie-setmixer");
    tinymix_set_value(mixer, control1, &values, 1);
    tinymix_set_value(mixer, control2, &values, 1);

    mixer_close(mixer);

    return 0;
}

3.tinymix-tinymix_list_controls

这边可以显示出所有的mixer配置的音频参数通道以及通过tinymix_detail_control查看通道现在的值，具体使用方法如下图所示。

static void tinymix_list_controls(struct mixer *mixer)
{
    struct mixer_ctl *ctl;
    const char *name, *type;
    unsigned int num_ctls, num_values;
    unsigned int i;

    num_ctls = mixer_get_num_ctls(mixer);

    printf("Number of controls: %u\n", num_ctls);

    if (g_tabs_only)
        printf("ctl\ttype\tnum\tname\tvalue");
    else
        printf("ctl\ttype\tnum\t%-40s value\n", "name");
    if (g_all_values)
        printf("\trange/values\n");
    else
        printf("\n");
    for (i = 0; i < num_ctls; i++) {
        ctl = mixer_get_ctl(mixer, i);

        name = mixer_ctl_get_name(ctl);
        type = mixer_ctl_get_type_string(ctl);
        num_values = mixer_ctl_get_num_values(ctl);
        if (g_tabs_only)
            printf("%d\t%s\t%d\t%s\t", i, type, num_values, name);
        else
            printf("%d\t%s\t%d\t%-40s ", i, type, num_values, name);
        tinymix_detail_control(mixer, name, 0, g_all_values);
    }
}

4.tinymix-tinymix_detail_control

tinymix_detail_control接口目的就是查看具体音频通道的配置信息，具体使用方法如下图所示。

static int tinymix_detail_control(struct mixer *mixer, const char *control,
                                  int prefix, int print_all)
{
    struct mixer_ctl *ctl;
    enum mixer_ctl_type type;
    unsigned int num_values;
    unsigned int i;
    int min, max;
    int ret;
    char *buf = NULL;
    size_t len;
    unsigned int tlv_header_size = 0;
    const char *space = g_tabs_only ? "\t" : " ";

    if (isdigit(control[0]))
        ctl = mixer_get_ctl(mixer, atoi(control));
    else
        ctl = mixer_get_ctl_by_name(mixer, control);

    if (!ctl) {
        fprintf(stderr, "Invalid mixer control: %s\n", control);
        return ENOENT;
    }

    type = mixer_ctl_get_type(ctl);
    num_values = mixer_ctl_get_num_values(ctl);

    if (type == MIXER_CTL_TYPE_BYTE) {
        if (mixer_ctl_is_access_tlv_rw(ctl)) {
            tlv_header_size = TLV_HEADER_SIZE;
        }
        buf = calloc(1, num_values + tlv_header_size);
        if (buf == NULL) {
            fprintf(stderr, "Failed to alloc mem for bytes %d\n", num_values);
            return ENOENT;
        }

        len = num_values;
        ret = mixer_ctl_get_array(ctl, buf, len + tlv_header_size);
        if (ret < 0) {
            fprintf(stderr, "Failed to mixer_ctl_get_array\n");
            free(buf);
            return ENOENT;
        }
    }


    printf("shengjie-%s, num:%d", mixer_ctl_get_name(ctl), num_values);
    if (prefix)
        printf("%s:%s", mixer_ctl_get_name(ctl), space);

    for (i = 0; i < num_values; i++) {
        switch (type)
        {
        case MIXER_CTL_TYPE_INT:
            printf("%d", mixer_ctl_get_value(ctl, i));
            break;
        case MIXER_CTL_TYPE_BOOL:
            printf("%s", mixer_ctl_get_value(ctl, i) ? "On" : "Off");
            break;
        case MIXER_CTL_TYPE_ENUM:
            tinymix_print_enum(ctl, space, print_all);
            break;
        case MIXER_CTL_TYPE_BYTE:
            /* skip printing TLV header if exists */
            printf(" %02x", buf[i + tlv_header_size]);
            break;
        default:
            printf("unknown");
            break;
        }

        if (i < num_values - 1)
            printf("%s", space);
    }

    if (print_all) {
        if (type == MIXER_CTL_TYPE_INT) {
            min = mixer_ctl_get_range_min(ctl);
            max = mixer_ctl_get_range_max(ctl);
            printf("%s(dsrange %d->%d)", space, min, max);
        }
    }

    free(buf);

    printf("\n");
    return 0;
}

5.tinymix-tinymix_set_value

tinymix_set_value接口在tinymix使用中应该是最重要的，所有的配置都需要这个接口进行控制，应用层或Audio HAL层调用的set audio mixer参数都要通过mixer_open、tinymix_set_value、mixer_close接口。下图所示是包含配置增益的参数配置check。

static int tinymix_set_value(struct mixer *mixer, const char *control,
                             char **values, unsigned int num_values)
{
    struct mixer_ctl *ctl;
    enum mixer_ctl_type type;
    unsigned int num_ctl_values;
    unsigned int i;

    if (isdigit(control[0]))
        ctl = mixer_get_ctl(mixer, atoi(control));
    else
        ctl = mixer_get_ctl_by_name(mixer, control);

    if (!ctl) {
        fprintf(stderr, "Invalid mixer control: %s\n", control);
        return ENOENT;
    }

    type = mixer_ctl_get_type(ctl);
    num_ctl_values = mixer_ctl_get_num_values(ctl);

    if (type == MIXER_CTL_TYPE_BYTE) {
        tinymix_set_byte_ctl(ctl, values, num_values);
        return ENOENT;
    }

    if (isdigit(values[0][0])) {
        if (num_values == 1) {
            /* Set all values the same */
            int value = atoi(values[0]);

            for (i = 0; i < num_ctl_values; i++) {
                if (mixer_ctl_set_value(ctl, i, value)) {
                    fprintf(stderr, "Error: invalid value\n");
                    return EINVAL;
                }
            }
        } else {
            /* Set multiple values */
            if (num_values > num_ctl_values) {
                fprintf(stderr,
                        "Error: %u values given, but control only takes %u\n",
                        num_values, num_ctl_values);
                return EINVAL;
            }
            for (i = 0; i < num_values; i++) {
                if (mixer_ctl_set_value(ctl, i, atoi(values[i]))) {
                    fprintf(stderr, "Error: invalid value for index %d\n", i);
                    return EINVAL;
                }
            }
        }
    } else {
        if (type == MIXER_CTL_TYPE_ENUM) {
            if (num_values != 1) {
                fprintf(stderr, "Enclose strings in quotes and try again\n");
                return EINVAL;
            }
            if (mixer_ctl_set_enum_by_string(ctl, values[0])) {
                fprintf(stderr, "Error: invalid enum value\n");
                return EINVAL;
            }
        } else {
            fprintf(stderr, "Error: only enum types can be set with strings\n");
            return EINVAL;
        }
    }

    return 0;
}