Alsa 播放从 CAN FD 获取的音频

Question

我正在尝试使用 Alsa 库将我从 CAN FD 通信中获得的音频复制到我的耳机中。我不太明白如何正确配置 Alsa 的参数，以便能够听到我从 CAN FD 获得的声音。

static char *device = "plughw:0,0"; /* playback device */
static snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE; /* sample format */
static unsigned int rate = 16000; /* stream rate */
static unsigned int channels = 1; /* count of channels */
static unsigned int buffer_time = 40000; /* ring buffer length in us */
static unsigned int period_time = 120000; /* period time in us */
static int resample = 1; /* enable alsa-lib resampling */
static int period_event = 0;                            /* produce poll event after each period */
int size;

while (1) {
        do {
            nbytes = read(s, &frame, sizeof(struct canfd_frame));
        } while (nbytes == 0);
        for (x = 0; x < 64; x = x + 2) {
            buffer[a] = ((uint32_t) frame.data[x] << 8)
                    | ((uint32_t) (frame.data[x + 1]));
            a++;
        }
        //err=snd_pcm_writei(handle,buffer,32);
        //printf("Datos = %d\n", err);
        memcpy(total1 + i * 32, buffer, 32 * sizeof(uint32_t));
        i++;
        a = 0;
        if (i == 500) {
            buffer_length=16000;
            ptr = total1;
            while(buffer_length > 0){
                err = snd_pcm_writei(handle, ptr, 16000);
                printf("Datos = %d\n", err);
                snd_pcm_avail_delay(handle, &availp, &delayp);
                //printf("available frames =%ld  delay = %ld  z = %d\n", availp, delayp, z);
                if (err == -EAGAIN)
                    continue;
                if(err < 0){
                    err=snd_pcm_recover(handle, err, 1);
                }
                else{
                    ptr += err * channels;
                    buffer_length -= err;
                    z++;
                }
                if(err<0){
                    printf("snd_pcm_writei failed: %s\n", snd_strerror(err));
                    break;
                }
        }
        i = 0;
    }

这是我的代码的一部分，我认为不值得发布整个代码。我不明白我应该给 buffer_time、period_time 哪些值，以及如何能够实时收听我通过 CAN FD 获得的信息。我正在使用 snd_pcm_writei，插入一个缓冲区，其中填充了一些从 CAN FD 获得的样本。我不知道我应该给缓冲区和“帧”变量设置多大的大小，这是另一个我不太了解的变量，尽管我已经阅读了一些相关内容。

知道我应该如何配置我的系统吗？ (buffer_time, period_time, buffer_size, 帧,...) 我尝试过使用不同的缓冲区和帧大小，但我认为我不明白它是如何正常工作的。如何计算 snd_pcm_writei() 的帧和缓冲区的大小，以便实时收听音频？

我应该使用两个不同的线程吗？一个用 CAN FD 信息创建缓冲区，另一个处理缓冲区和音频输出？

提前致谢，安德.

Answer 1

我终于可以通过耳机听到自己的声音了。我已经更改了我以前的配置 posted，以便用我从 CAN FD 获得的数据对其进行同步。我将 post 部分代码放在这里，以防有人需要示例。必须处理此类缓冲区的最重要部分是处理填充时间和通信时间。相应地处理时间和配置 Alsa 参数可以更容易地处理缓冲区。

static char *device = "plughw:0,0"; /* playback device */
static snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE; /* sample format */
static unsigned int rate = 22000; /* stream rate */ 
static unsigned int channels = 1; /* count of channels */
static unsigned int buffer_time = 1000; /* ring buffer length in us */ 
static unsigned int period_time = 10000; /* period time in us */ 
static int resample = 1; /* enable alsa-lib resampling */
static int period_event = 0; /* produce poll event after each period */
int size;

static snd_pcm_sframes_t buffer_size;
static snd_pcm_sframes_t period_size;
static snd_output_t *output = NULL;
snd_pcm_sframes_t delayp;
snd_pcm_sframes_t availp;

snd_pcm_uframes_t frames;

static void write_loop(snd_pcm_t *handle) {

    uint32_t *buffer = malloc(16000 * sizeof(uint32_t));

    uint32_t *total1 = malloc(16000 * sizeof(uint32_t)); // array to hold the result

    while (1) {
        do {
            nbytes = read(s, &frame, sizeof(struct canfd_frame));
        } while (nbytes == 0);
        for (x = 0; x < 64;x = x + 2) {
            buffer[a] = ((uint32_t) frame.data[x] << 8)
                    | ((uint32_t) (frame.data[x + 1]));
            //buffer[a]=frame.data[x];
            a++;
        }
        i++;
        if (i == 250) {
            memcpy(total1, buffer, 16000 * sizeof(uint32_t));
            //printf("Address = %lu \n",(unsigned long)total1);
            flag = 1;
            buffer_length = 16000;
            i = 0;
            a = 0;
        }
        if (flag == 1) {
            while(buffer_length > 0) {
                 snd_pcm_prepare(handle);
                err = snd_pcm_writei(handle, total1, buffer_length);
                //printf("Datos = %d\n", err);
                snd_pcm_avail_delay(handle, &availp, &delayp);
                 //printf("available frames =%ld  delay = %ld\n",availp,delayp);
                if (err == -EAGAIN)
                    continue;
                if (err < 0) {
                    err = snd_pcm_recover(handle, err, 1);
                } else {
                    ptr += err * channels;
                    buffer_length -= err;
                    z++;
                }
                if (err < 0) {
                    printf("snd_pcm_writei failed: %s\n", snd_strerror(err));
                    break;
                }
            }
            flag = 0;
        }
    }
}

Alsa 播放从 CAN FD 获取的音频

Alsa plays audio get from CAN FD

c

can-bus

alsa

embedded-linux