alsa声卡dev-snd-pcmC0D0p的open打开流程

alsa声卡/dev/snd/pcmC0D0p的open打开流程原文地址：/space.php?uid=20564848&do=blog&cuid=2116725aplay.c= main= snd_pcm_open(&handle, pcm_name, stream, open_mode); / 打开一路pcm,刷新config配置如果是default,同时type等于SND_CONFIG_TYPE_COMPOUND那么这里对应emptystatic const char *const build_in_pcms = adpcm, alaw, copy, dmix, file, hooks, hw, ladspa, lfloat, linear, meter, mulaw, multi, null, empty, plug, rate, route, share, shm, dsnoop, dshare, asym, iec958, softvol, mmap_emul, NULL;_snd_pcm_empty_open和snd_pcm_open_named_slave= snd_pcm_open_conf(pcmp, name, root, conf, stream, mode);= open_func = snd_dlobj_cache_lookup(open_name);将获得lib库中_snd_pcm_empty_open函数 所以open_func将等于_snd_pcm_empty_open _snd_pcm_empty_open _snd_pcm_asym_open _snd_pcm_plug_open _snd_pcm_softvol_open _snd_pcm_dmix_open _snd_pcm_hw_open = snd_pcm_hw_open(pcmp, name, card, device, subdevice, stream, mode | (nonblock ? SND_PCM_NONBLOCK : 0), 0, sync_ptr_ioctl);= snd_ctl_hw_openfilename等于/dev/snd/controlC0= snd_open_device(filename, fmode); ctl-ops = &snd_ctl_hw_ops; ctl-private_data = hw; ctl-poll_fd = fd; *handle = ctl;filename等于/dev/snd/pcmC0D0p= fd = snd_open_device(filename, fmode);= return snd_pcm_hw_open_fd(pcmp, name, fd, 0, sync_ptr_ioctl);= snd_pcm_new(&pcm, SND_PCM_TYPE_HW, name, info.stream, mode); pcm-ops = &snd_pcm_hw_ops; pcm-fast_ops = &snd_pcm_hw_fast_ops;static int snd_pcm_hw_mmap_control(snd_pcm_t *pcm) snd_pcm_hw_t *hw = pcm-private_data; void *ptr; int err; if (hw-sync_ptr = NULL) / 如果还没有mmap,那么执行mmap映射内核空间驱动使用的声音缓冲区 ptr = mmap(NULL, page_align(sizeof(struct sndrv_pcm_mmap_control), PROT_READ|PROT_WRITE, MAP_FILE|MAP_SHARED, hw-fd, SNDRV_PCM_MMAP_OFFSET_CONTROL); if (ptr = MAP_FAILED | ptr = NULL) err = -errno; SYSMSG(control mmap failed); return err; hw-mmap_control = ptr; / 声卡驱动头部填充了一个结构体sndrv_pcm_mmap_control,类似qvfb显示原理./ struct sndrv_pcm_mmap_control / sndrv_pcm_uframes_t appl_ptr; /* RW: appl ptr (0.boundary-1) */ sndrv_pcm_uframes_t avail_min; /* RW: min available frames for wakeup */ ; else hw-mmap_control-avail_min = 1; snd_pcm_set_appl_ptr(pcm, &hw-mmap_control-appl_ptr, hw-fd, SNDRV_PCM_MMAP_OFFSET_CONTROL); return 0;snd_pcm_mmap switch (i-type) case SND_PCM_AREA_MMAP: / 表示为数据区分配驱动内存,在snd_pcm_hw_channel_info中设置了type ptr = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_FILE|MAP_SHARED, i-u.mmap.fd, i-u.mmap.offset);/*mmap= snd_pcm_mmap_data= snd_pcm_default_mmap/ mmap the DMA buffer on RAMstatic int snd_pcm_default_mmap(struct snd_pcm_substream *substream, struct vm_area_struct *area) area-vm_ops = &snd_pcm_vm_ops_data; / vma操作函数,当应用程序向该area读写不存在的内存数据时, area-vm_private_data = substream; / 将执行snd_pcm_vm_ops_data中的fault / 函数snd_pcm_mmap_data_fault进一步以页为单位申请内存空间,所以如果用户程序需要64k,那么将执行16次,每次申请4k空间luther.gliethttp. area-vm_flags |= VM_RESERVED; atomic_inc(&substream-mmap_count); return 0;*/ if (ptr = MAP_FAILED) SYSERR(mmap failed); return -errno; i-addr = ptr;= snd_pcm_mmap_controlstatic int snd_pcm_mmap_control(struct snd_pcm_substream *substream, struct file *file, struct vm_area_struct *area) struct snd_pcm_runtime *runtime; long size; if (!(area-vm_flags & VM_READ) return -EINVAL; runtime = substream-runtime; size = area-vm_end - area-vm_start; if (size != PAGE_ALIGN(sizeof(struct snd_pcm_mmap_control) return -EINVAL; area-vm_ops = &snd_pcm_vm_ops_control; / 当对( area-vm_start,area-vm_end)之间空间操作,发生 area-vm_private_data = substream; / 缺页时,内核将调用该vm_ops方法来处理fault异常, area-vm_flags |= VM_RESERVED; / 进而执行snd_pcm_mmap_control_fault申请1个page空间 return 0;= writei_func = snd_pcm_writei;= playback(argvoptind+);= playback_go(fd, dtawave, pbrec_count, FORMAT_WAVE, name);= pcm_write(audiobuf, l);= writei_func(handle, data, count);就是调用上面的snd_pcm_writei= snd_pcm_writei= _snd_pcm_writei= pcm-fast_ops-writei(pcm-fast_op_arg, buffer, size);= snd_pcm_plugin_writei= snd_pcm_write_areas(pcm, areas, 0, size, snd_pcm_plugin_write_areas);= avail = snd_pcm_avail_update(pcm); / 获取可用缓冲区位置偏移索引值= func()就是snd_pcm_plugin_write_areas函数发送1024帧音频数据,一帧对应一次完整采样,比如stereo立体声,24bits量化,那么这里一帧对应3*2字节数据,即一次完整采样所需空间luther.gliethttp.= plugin-write(pcm, areas, offset, frames, slave_areas, slave_offset, &slave_frames);即调用snd_pcm_linear_write_areas函数将areas中的frames频数据拷贝到slave_areas内存区= pcm-fast_ops-mmap_commit(pcm-fast_op_arg, offset, frames);= snd_pcm_dmix_mmap_commit= snd_pcm_dmix_sync_area/* synchronize shm ring buffer with hardware*/static void snd_pcm_dmix_sync_area(snd_pcm_t *pcm)= /* add sample areas here */ src_areas = snd_pcm_mmap_areas(pcm); dst_areas = snd_pcm_mmap_areas(dmix-spcm); / 添加= mix_areas(dmix, src_areas, dst_areas, appl_ptr, slave_appl_ptr, transfer); if (dmix-interleaved) / 可以将缓冲中的音频数据填充到硬件中luther.gliethttp /* * process all areas in one loop * it optimizes the memory accesses for this case */ do_mix_areas(size * channels, (unsigned char *)dst_areas0.addr + sample_size * dst_ofs * channels, (unsigned char *)src_areas0.addr + sample_size * src_ofs * channels, dmix-u.dmix.sum_buffer + dst_ofs * channels, sample_size, sample_size, sizeof(signed int); return; = do_mix_areas(size * channels, (unsigned char *)dst_areas0.addr + sample_size * dst_ofs * channels, (unsigned char *)src_areas0.addr + sample_size * src_ofs * channels, dmix-u.dmix.sum_buffer + dst_ofs * channels, sample_size, sample_size, sizeof(signed int);这里的do_mix_areas在i386中,使用下面完全用汇编实现的拷贝函数MIX_AREAS_32完成数据从src到dst的快速拷贝,每拷贝一次,声卡就会发出一点声音luther.gliethttp/* for plain i386, 32-bit version (24-bit resolution)*/static void MIX_AREAS_32(unsigned int size, volatile signed int *dst, signed int *src, volatile signed int *sum, size_t dst_step, size_t src_step, size_t sum_step)_snd_pcm_asym_open_snd_pcm_dmix_opensnd_pcm_plugin_avail_update= snd_pcm_avail_update(slave);= pcm-fast_ops-avail_update(pcm-fast_op_arg);= snd_pcm_dmix_avail_update= snd_pcm_mmap_playback_avail(pcm);alsa_sound_init#define CONFIG_SND_MAJOR 116 /* standard configuration */static int major = CONFIG_SND_MAJOR;module_init(alsa_sound_init)alsa_sound_init= register_chrdev(major, alsa, &snd_fops) / 主设备号为116的所有设备都为alsa设备,节点方法集为snd_fopsstatic const struct file_operations snd_fops = / alsa的设备名为pcmC0D1c或pcmC0D1p等luther.gliethttp. .owner = THIS_MODULE, .open = snd_open;snd_open= _snd_open(inode, file);= _snd_open unsigned int minor = iminor(inode); mptr = snd_minorsminor; file-f_op = fops_get(mptr-f_ops); file-f_op-open(inode, file);const struct file_operations snd_pcm_f_ops2 = / alsa使用到的SNDRV_PCM_STREAM_PLAYBACK放音方法集luther.gliethttp .owner = THIS_MODULE, .write = snd_pcm_write, .aio_write = snd_pcm_aio_write, .open = snd_pcm_playback_open, .release = snd_pcm_release, .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 = dummy_get_unmapped_area, , / alsa使用到的SNDRV_PCM_STREAM_CAPTURE录音方法集luther.gliethttp .owner = THIS_MODULE, .read = snd_pcm_read, .aio_read = snd_pcm_aio_read, .open = snd_pcm_capture_open, .release = snd_pcm_release, .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 = dummy_get_unmapped_area, ;=snd_intel8x0_probe= snd_intel8x0_create= request_irq(pci-irq, snd_intel8x0_interrupt, IRQF_SHARED,card-shortname, chip)snd_intel8x0_interruptsnd_intel8x0_updatesnd_open= snd_pcm_playback_open= snd_pcm_open= snd_pcm_open_file= snd_pcm_open_substream= substream-ops-open(substream)即snd_intel8x0_playback_ops.open= snd_intel8x0_playback_open= snd_intel8x0_pcm_openstatic int snd_intel8x0_pcm_open(struct snd_pcm_substream *substream, struct ichdev *ichdev) struct intel8x0 *chip = snd_pcm_substream_chip(substream); struct snd_pcm_runtime *runtime = substream-runtime; int err; ichdev-substream = substream; runtime-hw = snd_intel8x0_stream; / 声卡配置硬件信息luther.gliethttp runtime-hw.rates = ichdev-pcm-rates; snd_pcm_limit_hw_rates(runtime); if (chip-device_type = DEVICE_SIS) runtime-hw.buffer_bytes_max = 64*1024; runtime-hw.period_bytes_max = 64*1024; if (err = snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS) private_data = ichdev; return 0;ioctl(SNDRV_PCM_IOCTL_HW_PARAMS)= snd_pcm_f_ops.unlocked_ioctl即：snd_pcm_playback_ioctl= snd_pcm_playback_ioctl= snd_pcm_playback_ioctl1= snd_pcm_common_ioctl1 case SNDRV_PCM_IOCTL_HW_PARAMS: return snd_pcm_hw_params_user(substream, arg);= snd_pcm_hw_params_user= snd_pcm_hw_params= substream-ops-hw_params即snd_intel8x0_playback_ops.hw_params= snd_intel8x0_hw_params= snd_ac97_pcm_open(ichdev-pcm, params_rate(hw_params), params_channels(hw_params), ichdev-pcm-rdbl.slots);ioctl(SNDRV_PCM_IOCTL_PREPARE)= snd_pcm_playback_ioctl= snd_pcm_playback_ioctl1= snd_pcm_common_ioctl1= snd_pcm_prepare / prepare the PCM substream to be triggerable= snd_pcm_action_nonatomic(&snd_pcm_action_prepare, substream, f_flags);= snd_pcm_action_single(ops, substream, state); ops-pre_action(substream, state); ops-do_action(substream, state); ops-post_action(substream, state); 上面ops就是之前提到的snd_pcm_action_prepare= snd_pcm_do_prepare调用snd_pcm_do_reset(substream, 0);复位 substream-ops-prepare(substream);即snd_intel8x0_playback_ops.prepare= snd_intel8x0_pcm_preparestatic int snd_intel8x0_pcm_prepare(struct snd_pcm_substream *substream) struct intel8x0 *chip = snd_pcm_substream_chip(substream); struct snd_pcm_runtime *runtime = substream-runtime; struct ichdev *ichdev = get_ichdev(substream); ichdev-physbuf = runtime-dma_addr; / dma缓冲区地址 ichdev-size = snd_pcm_lib_buffer_bytes(substream); / 将帧缓冲大小转为字节空间大小luther.gliethttp ichdev-fragsize = snd_pcm_lib_period_bytes(substream); if (ichdev-ichd = ICHD_PCMOUT) snd_intel8x0_setup_pcm_out(chip, runtime); / 为play模式设置ac97寄存器luther.gliethttp if (chip-device_type = DEVICE_INTEL_ICH4) ichdev-pos_shift = (runtime-sample_bits 16) ? 2 : 1; snd_intel8x0_setup_periods(chip, ichdev); / 设置PCI总线ac97的bank地址空间luther.gliethttp return 0;= snd_intel8x0_setup_pcm_outstatic void snd_intel8x0_setup_pcm_out(struct intel8x0 *chip, struct snd_pcm_runtime *runtime) unsigned int cnt; int dbl = runtime-rate 48000;/ 一共有如下几种设备：enum DEVICE_INTEL, DEVICE_INTEL_ICH4, DEVICE_SIS, DEVICE_ALI, DEVICE_NFORCE ; spin_lock_irq(&chip-reg_lock); switch (chip-device_type) case DEVICE_ALI: cnt = igetdword(chip, ICHREG(ALI_SCR); cnt &= ICH_ALI_SC_PCM_246_MASK; if (runtime-channels = 4 | dbl) cnt |= ICH_ALI_SC_PCM_4; else if (runtime-channels = 6) cnt |= ICH_ALI_SC_PCM_6; iputdword(chip, ICHREG(ALI_SCR), cnt); break; case DEVICE_SIS: cnt = igetdword(chip, ICHREG(GLOB_CNT); cnt &= ICH_SIS_PCM_246_MASK; if (runtime-channels = 4 | dbl) cnt |= ICH_SIS_PCM_4; else if (runtime-channels = 6) cnt |= ICH_SIS_PCM_6; iputdword(chip, ICHREG(GLOB_CNT), cnt); break; default: cnt = igetdword(chip, ICHREG(GLOB_CNT); cnt &= (ICH_PCM_246_MASK | ICH_PCM_20BIT); if (runtime-channels = 4 | dbl) cnt |= ICH_PCM_4; else if (runtime-channels = 6) cnt |= ICH_PCM_6; else if (runtime-channels = 8) cnt |= ICH_PCM_8; if (chip-device_type = DEVICE_NFORCE) /* reset to 2ch once to keep the 6 channel data in alignment, * to start from Front Left always */ if (cnt & ICH_PCM_246_MASK) iputdword(chip, ICHREG(GLOB_CNT), cnt & ICH_PCM_246_MASK); spin_unlock_irq(&chip-reg_lock); msleep(50); /* grrr. */ spin_lock_irq(&chip-reg_lock); else if (chip-device_type = DEVICE_INTEL_ICH4) if (runtime-sample_bits 16) cnt |