#define ID_WAVE 0x45564157 //这个值是WAVE的ASCII值 #define ID_FMT 0x20746d66 #define ID_DATA 0x61746164 //这个值是DATA的ASCII值
main函数 header.riff_id = ID_RIFF; //这里是RIFF,标志符
header.riff_sz = 0; header.riff_fmt = ID_WAVE; // 格式类型WAVE header.fmt_id = ID_FMT; //波形文件标志:FMT(最后一位空格符) header.fmt_sz = 16; //数值是16或者18,18是有附带了信息 header.audio_format = FORMAT_PCM; //编码方式，一般是1 header.num_channels = channels; //声道数值，1是单声道，2是双声道 header.sample_rate = rate; //采样频率 format = PCM_FORMAT_S24_LE; //每个采样需要的bytes
header.bits_per_sample = pcm_format_to_bits(format); //转化为bit数
header.byte_rate = (header.bits_per_sample / 8) * channels * rate; //每秒传输的byte数 header.block_align = channels * (header.bits_per_sample / 8); //每个采样的byte数 header.data_id = ID_DATA; //Data Chunk,数据块
/* leave enough room for header */
fseek(file, sizeof(struct wav_header), SEEK_SET); //给header足够的空间 /* install signal handler and begin capturing */
signal(SIGINT, sigint_handler); //SIGINT ：来自键盘的中断信号 ( ctrl + c ) . //开始录制，单独分析1
frames = capture_sample(file, card, device, header.num_channels, header.sample_rate, format, period_size, period_count);
1.单独分析1unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device, unsigned int channels, unsigned int rate, enum pcm_format format, unsigned int period_size, unsigned int period_count) pcm = pcm_open(card, device, PCM_IN, &config); pcm->config = *config;
snprintf(fn, sizeof(fn), "/dev/snd/pcmC%uD%u%c", card, device, flags & PCM_IN ? 'c' : 'p'); pcm->fd = open(fn, O_RDWR); //打开/dev/snd/pcmC0D0c，与rk音频驱动分析之tinyplay播放类似
//获取pcm的信息，包括card，流，dma各种信息，与rk音频驱动分析之tinyplay播放类似
ioctl(pcm->fd, SNDRV_PCM_IOCTL_INFO, &info)
param_init(¶ms); //限制参数初始化
.............一些限制参数设置..............
param_set_flag(¶ms, config->flag);
//根据底层的限制，重新给params赋值，设置cpu dai和codec dai的类型和时钟等
ioctl(pcm->fd, SNDRV_PCM_IOCTL_HW_PARAMS, ¶ms) //与rk音频驱动分析之tinyplay播放类似
/* get our refined hw_params */
config->period_size = param_get_int(¶ms, SNDRV_PCM_HW_PARAM_PERIOD_SIZE); //得到period大小 config->period_count = param_get_int(¶ms, SNDRV_PCM_HW_PARAM_PERIODS); //数量 pcm->buffer_size = config->period_count * config->period_size; //总的buf大小 if (flags & PCM_MMAP) //如果是映射，
//mmap将一个文件或者其它对象映射进内存，调用底层的mmap函数，与rk音频驱动分析之tinyplay播放类似
pcm->mmap_buffer = mmap(NULL, pcm_frames_to_bytes(pcm, pcm->buffer_size),
PROT_READ | PROT_WRITE, MAP_FILE | MAP_SHARED, pcm->fd, 0); //包括一些period_step ，silence_threshold 等参数，与rk音频驱动分析之tinyplay播放类似
ioctl(pcm->fd, SNDRV_PCM_IOCTL_SW_PARAMS, &sparams) //主要是把上层的参数赋值给snd_pcm_runtime
//与rk音频驱动分析之tinyplay播放类似
rc = pcm_hw_mmap_status(pcm); //分配SNDRV_PCM_MMAP_OFFSET_CONTROL的内存映射，
#ifdef SNDRV_PCM_IOCTL_TTSTAMP
int arg = SNDRV_PCM_TSTAMP_TYPE_MONOTONIC;
rc = ioctl(pcm->fd, SNDRV_PCM_IOCTL_TTSTAMP, &arg); //设置为绝对时间 size = pcm_frames_to_bytes(pcm, pcm_get_buffer_size(pcm)); //得到ring buf的大小
buffer = malloc(size); //分配
while (capturing && !pcm_read(pcm, buffer, size)) //从PCM里面读取数据到buffer里面，单独分析2
if (fwrite(buffer, 1, size, file) != size) //把buf的数据写入到file
bytes_read += size; //+size
单独分析2
int pcm_read(struct pcm *pcm, void *data, unsigned int count) x.buf = data; //buf的地址
x.frames = count / (pcm->config.channels * pcm_format_to_bits(pcm->config.format) / 8); //表示有多少帧 for (;;)
if (!pcm->running)
if (pcm_start(pcm) < 0) //调用驱动预备pcm可以触发，这里就是搜索path，widgets相关，
ioctl(pcm->fd, SNDRV_PCM_IOCTL_PREPARE) //与rk音频驱动分析之tinyplay播放类似
ioctl(pcm->fd, SNDRV_PCM_IOCTL_READI_FRAMES, &x) //这里调用驱动进行读取操作，驱动分析一
二.驱动分析一调用snd_pcm_capture_ioctl的snd_pcm_capture_ioctl1函数static int snd_pcm_capture_ioctl1(struct file *file, struct snd_pcm_substream *substream, unsigned int cmd, void __user *arg) switch (cmd)
case SNDRV_PCM_IOCTL_READI_FRAMES:
struct snd_xferi __user *_xferi = arg; //获取应用传来的参数
copy_from_user(&xferi, _xferi, sizeof(xferi)) //把_xferi参数结构体从用户空间拷贝过来
result = snd_pcm_lib_read(substream, xferi.buf, xferi.frames); //读取数据
err = pcm_sanity_check(substream); //检查有不有读写函数
//用snd_pcm_lib_read_transfer函数读取数据，单独分析1
snd_pcm_lib_read1(substream, (unsigned long)buf, size, nonblock, snd_pcm_lib_read_transfer);
单独分析1
static snd_pcm_sframes_t snd_pcm_lib_read1(struct snd_pcm_substream *substream, unsigned long data, snd_pcm_uframes_t size, int nonblock, transfer_f transfer) switch (runtime->status->state)
case SNDRV_PCM_STATE_PREPARED:
//开始传输，与rk音频驱动分析之tinyplay播放相似，我们这里是录音，通路方向不一样
//主要是启动DMA开始读取数据，然后启动I2S开始读取codec的数据
err = snd_pcm_start(substream); //start all linked streams
........
if (runtime->status->state == SNDRV_PCM_STATE_RUNNING)
snd_pcm_update_hw_ptr(substream); //更新ring buf相关的位置
avail = snd_pcm_capture_avail(runtime); //获取DMA已经写入的ring缓冲区大小，就是可读数据的大小
snd_pcm_sframes_t avail = runtime->status->hw_ptr - runtime->control->appl_ptr;
while (size > 0)
if (!avail) //没有可读的数据
if (runtime->status->state == SNDRV_PCM_STATE_DRAINING) //暂时不知道 snd_pcm_stop(substream, SNDRV_PCM_STATE_SETUP); //停止
if (nonblock) //如果是非阻塞，直接返回
err = -EAGAIN;
err = wait_for_avail(substream, &avail); //等待
frames = size > avail ? avail : size; //读取的大小
//这里还没有搞懂
cont = runtime->buffer_size - runtime->control->appl_ptr % runtime->buffer_size;
if (frames > cont) frames = cont; appl_ptr = runtime->control->appl_ptr; //读指针的值
appl_ofs = appl_ptr % runtime->buffer_size; //读指针在buf里面的偏移 err = transfer(substream, appl_ofs, data, offset, frames); //单独分析2，这里是把数据拷贝给user
appl_ptr += frames; //读地址加刚才拷贝的数据大小
if (appl_ptr >= runtime->boundary) //循环
appl_ptr -= runtime->boundary;
runtime->control->appl_ptr = appl_ptr;
if (substream->ops->ack) //这里没有
substream->ops->ack(substream); offset += frames; //偏移增加
size -= frames; //size减少 xfer += frames; //传输xfer增加 avail -= frames; //可读的减少
2.单独分析2
static int snd_pcm_lib_read_transfer(struct snd_pcm_substream *substream, unsigned int hwoff, unsigned long data, unsigned int off, snd_pcm_uframes_t frames) //获取buf的地址，这里off是偏移地址
char __user *buf = (char __user *) data + frames_to_bytes(runtime, off);
if (substream->ops->copy) //这里没有
err = substream->ops->copy(substream, -1, hwoff, buf, frames)
else
char *hwbuf = runtime->dma_area + frames_to_bytes(runtime, hwoff); //获取ring buf读的地址
copy_to_user(buf, hwbuf, frames_to_bytes(runtime, frames)) //把dma的从hwbuf开始的数据拷贝到user，大小为frames