ALSA驱动框架

╰半橙微兮° 2022-01-11 16:49 395阅读 0赞

*  1.  linux框架  
        ![20190620151731639.png][]
    2.  软件框架部分， 声卡驱动属于字符驱动，满足字符驱动模型
    
        inux-3.4.2\sound\core\sound.c
        static int __init alsa_sound_init(void)
        {
                snd_major = major;
                register_chrdev(major, "alsa", &snd_fops)) 
        
        }
        
        static const struct file_operations snd_fops =
        {
                .owner =        THIS_MODULE,
                .open =         snd_open,
                .llseek =       noop_llseek,
        };
    
    分析snd\_open，
    
        struct snd_minor {
                int type;                       /* SNDRV_DEVICE_TYPE_XXX */
                int card;                       /* card number */
                int device;                     /* device number */
                const struct file_operations *f_ops;    /* file operations */
                void *private_data;             /* private data for f_ops->open */
                struct device *dev;             /* device for sysfs */
        };
        
        #define SNDRV_OS_MINORS                 256
        struct snd_minor *mptr = NULL;
        static struct snd_minor *snd_minors[SNDRV_OS_MINORS];
        
        mptr = snd_minors[minor];
        old_fops = file->f_op;
        file->f_op = fops_get(mptr->f_ops);
        
        fops_put(old_fops);
    
    1.  分析声卡驱动流程
    
    ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hhcHB5Z3JpbGNsaA_size_16_color_FFFFFF_t_70][]
    
    pcm.c 中的 snd\_pcm\_f\_ops\[2\]，1表示录音，0表示播放。
    
        const struct file_operations snd_pcm_f_ops[2] = {
                {
                        .owner =                THIS_MODULE,
                        .write =                snd_pcm_write,
                        .aio_write =            snd_pcm_aio_write,
                        .open =                 snd_pcm_playback_open,
                        .release =              snd_pcm_release,
                        .llseek =               no_llseek,
                        .poll =                 snd_pcm_playback_poll,
                        .unlocked_ioctl =       snd_pcm_playback_ioctl,
                        .compat_ioctl =         snd_pcm_ioctl_compat,
                        .mmap =                 snd_pcm_mmap,
                        .fasync =               snd_pcm_fasync,
                        .get_unmapped_area =    snd_pcm_get_unmapped_area,
                },
                {
                        .owner =                THIS_MODULE,
                        .read =                 snd_pcm_read,
                        .aio_read =             snd_pcm_aio_read,
                        .open =                 snd_pcm_capture_open,
                        .release =              snd_pcm_release,
                        .llseek =               no_llseek,
                        .poll =                 snd_pcm_capture_poll,
                        .unlocked_ioctl =       snd_pcm_capture_ioctl,
                        .compat_ioctl =         snd_pcm_ioctl_compat,
                        .mmap =                 snd_pcm_mmap,
                        .fasync =               snd_pcm_fasync,
                        .get_unmapped_area =    snd_pcm_get_unmapped_area,
                }
        };
    
        函数：snd_register_device_for_dev
        
           struct snd_minor *preg;
        
                if (snd_BUG_ON(!name))
                        return -EINVAL;
                preg = kmalloc(sizeof *preg, GFP_KERNEL);
                if (preg == NULL)
                        return -ENOMEM;
                preg->type = type;
                preg->card = card ? card->number : -1;
                preg->device = dev;
                preg->f_ops = f_ops;
                preg->private_data = private_data;
            
            。。。。。。。。。。。。。。
            
            snd_minors[minor] = preg;
                preg->dev = device_create(sound_class, device, MKDEV(major, minor),
                                          private_data, "%s", name);
    
    知识点回顾：
    
    字符驱动：
    
    1.  构造file\_operations
    2.  为了自动创建设备节点，得创建class ,创建class\_device
    
    so ，preg->dev = device\_create(sound\_class, device, MKDEV(major, minor),  
    private\_data, "%s", name);
    
        register_chrdev
        class_create
        class_device_create
        
        
        sound\core\sound.c 
        static int __init alsa_sound_init(void) 
        { 
        snd_major = major; 
        register_chrdev(major, "alsa", &snd_fops))
        }
        
        sound\sound_core.c
        static int __init init_soundcore(void)
        {
                int rc;
        
                rc = init_oss_soundcore();
                if (rc)
                        return rc;
        
                sound_class = class_create(THIS_MODULE, "sound");
                if (IS_ERR(sound_class)) {
                        cleanup_oss_soundcore();
                        return PTR_ERR(sound_class);
                }
        
                sound_class->devnode = c;
        
                return 0;
        }
    
    关注class\_device 的name.
    
        一路：
        preg->dev = device_create(sound_class, device, MKDEV(major, minor),
                                          private_data, "%s", name);
                          
        static int snd_ctl_dev_register(struct snd_device *device)
        {
                sprintf(name, "controlC%i", cardnum);
            
         }
         
         
         另一路：
         err = snd_register_device_for_dev(devtype, pcm->card,
                                                          pcm->device,
                                                          &snd_pcm_f_ops[cidx],
                                                          pcm, str, dev);
                                  
         switch (cidx) {
                        case SNDRV_PCM_STREAM_PLAYBACK:
                                sprintf(str, "pcmC%iD%ip", pcm->card->number, pcm->device);
                                devtype = SNDRV_DEVICE_TYPE_PCM_PLAYBACK;
                                break;
                        case SNDRV_PCM_STREAM_CAPTURE:
                                sprintf(str, "pcmC%iD%ic", pcm->card->number, pcm->device);
                                devtype = SNDRV_DEVICE_TYPE_PCM_CAPTURE;
                                break;
                        }
    
    1.  alsa 声卡驱动的步骤：
        
        1.  snd\_cad\_create
        2.  初始化  
            snd\_pcm\_new
        3.  注册  
            snd\_card\_register

[20190620151731639.png]: /images/20220110/59c41c67e7894b4e904df0e53eea580e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hhcHB5Z3JpbGNsaA_size_16_color_FFFFFF_t_70]: /images/20220110/eda2903314144c9d81d8b993e0eb875f.png