Linux音频驱动之二:声卡的创建
Linux音频驱动之二:声卡的创建
1. struct snd_card
1.1. snd_card是什么
snd_card可以说是整个ALSA音频驱动最顶层的一个结构,整个声卡的软件逻辑结构开始于该结构,几乎所有与声音相关的逻辑设备都是在snd_card的管理之下,声卡驱动的第一个动作通常就是创建一个snd_card结构体。正因为如此,本节中,我们也从 struct cnd_card开始吧。
Linux音频驱动之一:ALSA架构简介
1.2. snd_card的定义
snd_card的定义位于改头文件中:include/sound/core.h
- /* main structure for soundcard */
- struct snd_card {
- int number; /* number of soundcard (index to
- snd_cards) */
- char id[16]; /* id string of this card */
- char driver[16]; /* driver name */
- char shortname[32]; /* short name of this soundcard */
- char longname[80]; /* name of this soundcard */
- char mixername[80]; /* mixer name */
- char components[128]; /* card components delimited with
- space */
- struct module *module; /* top-level module */
- void *private_data; /* private data for soundcard */
- void (*private_free) (struct snd_card *card); /* callback for freeing of
- private data */
- struct list_head devices; /* devices */
- unsigned int last_numid; /* last used numeric ID */
- struct rw_semaphore controls_rwsem; /* controls list lock */
- rwlock_t ctl_files_rwlock; /* ctl_files list lock */
- int controls_count; /* count of all controls */
- int user_ctl_count; /* count of all user controls */
- struct list_head controls; /* all controls for this card */
- struct list_head ctl_files; /* active control files */
- struct snd_info_entry *proc_root; /* root for soundcard specific files */
- struct snd_info_entry *proc_id; /* the card id */
- struct proc_dir_entry *proc_root_link; /* number link to real id */
- struct list_head files_list; /* all files associated to this card */
- struct snd_shutdown_f_ops *s_f_ops; /* file operations in the shutdown
- state */
- spinlock_t files_lock; /* lock the files for this card */
- int shutdown; /* this card is going down */
- int free_on_last_close; /* free in context of file_release */
- wait_queue_head_t shutdown_sleep;
- struct device *dev; /* device assigned to this card */
- #ifndef CONFIG_SYSFS_DEPRECATED
- struct device *card_dev; /* cardX object for sysfs */
- #endif
- #ifdef CONFIG_PM
- unsigned int power_state; /* power state */
- struct mutex power_lock; /* power lock */
- wait_queue_head_t power_sleep;
- #endif
- #if defined(CONFIG_SND_MIXER_OSS) || defined(CONFIG_SND_MIXER_OSS_MODULE)
- struct snd_mixer_oss *mixer_oss;
- int mixer_oss_change_count;
- #endif
- };
- struct list_head devices 记录该声卡下所有逻辑设备的链表
- struct list_head controls 记录该声卡下所有的控制单元的链表
- void *private_data 声卡的私有数据,可以在创建声卡时通过参数指定数据的大小
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