一.Tinycap分析
使用命令：tinycap /sdcard/test.wav -D card0 -d device0 -c 2 -r 48000 -b 16 -p 1024 -n 16
Tinycap.c (external\tinyalsa)
錄音流程：
#define ID_RIFF 0x46464952 //這個值是RIFF的ASCII值
#define ID_WAVE 0x45564157 //這個值是WAVE的ASCII值
#define ID_FMT 0x20746d66
#define ID_DATA 0x61746164 //這個值是DATA的ASCII值
main函數
header.riff_id = ID_RIFF; //這里是RIFF,標志符
header.riff_sz = 0;
header.riff_fmt = ID_WAVE; // 格式類型WAVE
header.fmt_id = ID_FMT; //波形文件標志:FMT(最后一位空格符)
header.fmt_sz = 16; //數值是16或者18,18是有附帶了信息
header.audio_format = FORMAT_PCM; //編碼方式，一般是1
header.num_channels = channels; //聲道數值，1是單聲道，2是雙聲道
header.sample_rate = rate; //采樣頻率
format = PCM_FORMAT_S24_LE; //每個采樣需要的bytes
header.bits_per_sample = pcm_format_to_bits(format); //轉化為bit數
header.byte_rate = (header.bits_per_sample / 8) * channels * rate; //每秒傳輸的byte數
header.block_align = channels * (header.bits_per_sample / 8); //每個采樣的byte數
header.data_id = ID_DATA; //Data Chunk,數據塊
/* leave enough room for header */
fseek(file, sizeof(struct wav_header), SEEK_SET); //給header足夠的空間
/* install signal handler and begin capturing */
signal(SIGINT, sigint_handler); //SIGINT ：來自鍵盤的中斷信號 ( ctrl + c ) .
//開始錄制，單獨分析1
frames = capture_sample(file, card, device, header.num_channels, header.sample_rate, format, period_size, period_count);
1.單獨分析1
unsigned 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); //打開/dev/snd/pcmC0D0c，與rk音頻驅動分析之tinyplay播放類似
//獲取pcm的信息，包括card，流，dma各種信息，與rk音頻驅動分析之tinyplay播放類似
ioctl(pcm->fd, SNDRV_PCM_IOCTL_INFO, &info)
param_init(¶ms); //限制參數初始化
.............一些限制參數設置..............
param_set_flag(¶ms, config->flag);
//根據底層的限制，重新給params賦值，設置cpu dai和codec dai的類型和時鍾等
ioctl(pcm->fd, SNDRV_PCM_IOCTL_HW_PARAMS, ¶ms) //與rk音頻驅動分析之tinyplay播放類似
/* 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); //數量
pcm->buffer_size = config->period_count * config->period_size; //總的buf大小
if (flags & PCM_MMAP) //如果是映射，
//mmap將一個文件或者其它對象映射進內存，調用底層的mmap函數，與rk音頻驅動分析之tinyplay播放類似
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 等參數，與rk音頻驅動分析之tinyplay播放類似
ioctl(pcm->fd, SNDRV_PCM_IOCTL_SW_PARAMS, &sparams) //主要是把上層的參數賦值給snd_pcm_runtime
//與rk音頻驅動分析之tinyplay播放類似
rc = pcm_hw_mmap_status(pcm); //分配SNDRV_PCM_MMAP_OFFSET_CONTROL的內存映射，
#ifdef SNDRV_PCM_IOCTL_TTSTAMP
int arg = SNDRV_PCM_TSTAMP_TYPE_MONOTONIC;
rc = ioctl(pcm->fd, SNDRV_PCM_IOCTL_TTSTAMP, &arg); //設置為絕對時間
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)) //從PCM里面讀取數據到buffer里面，單獨分析2
if (fwrite(buffer, 1, size, file) != size) //把buf的數據寫入到file
bytes_read += size; //+size
單獨分析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); //表示有多少幀
for (;;)
if (!pcm->running)
if (pcm_start(pcm) < 0) //調用驅動預備pcm可以觸發，這里就是搜索path，widgets相關，
ioctl(pcm->fd, SNDRV_PCM_IOCTL_PREPARE) //與rk音頻驅動分析之tinyplay播放類似
ioctl(pcm->fd, SNDRV_PCM_IOCTL_READI_FRAMES, &x) //這里調用驅動進行讀取操作，驅動分析一
二.驅動分析一
調用snd_pcm_capture_ioctl的snd_pcm_capture_ioctl1函數
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; //獲取應用傳來的參數
copy_from_user(&xferi, _xferi, sizeof(xferi)) //把_xferi參數結構體從用戶空間拷貝過來
result = snd_pcm_lib_read(substream, xferi.buf, xferi.frames); //讀取數據
err = pcm_sanity_check(substream); //檢查有不有讀寫函數
//用snd_pcm_lib_read_transfer函數讀取數據，單獨分析1
snd_pcm_lib_read1(substream, (unsigned long)buf, size, nonblock, snd_pcm_lib_read_transfer);
單獨分析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:
//開始傳輸，與rk音頻驅動分析之tinyplay播放相似，我們這里是錄音，通路方向不一樣
//主要是啟動DMA開始讀取數據，然后啟動I2S開始讀取codec的數據
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相關的位置
avail = snd_pcm_capture_avail(runtime); //獲取DMA已經寫入的ring緩沖區大小，就是可讀數據的大小
snd_pcm_sframes_t avail = runtime->status->hw_ptr - runtime->control->appl_ptr;
while (size > 0)
if (!avail) //沒有可讀的數據
if (runtime->status->state == SNDRV_PCM_STATE_DRAINING) //暫時不知道
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; //讀取的大小
//這里還沒有搞懂
cont = runtime->buffer_size - runtime->control->appl_ptr % runtime->buffer_size;
if (frames > cont)
frames = cont;
appl_ptr = runtime->control->appl_ptr; //讀指針的值
appl_ofs = appl_ptr % runtime->buffer_size; //讀指針在buf里面的偏移
err = transfer(substream, appl_ofs, data, offset, frames); //單獨分析2，這里是把數據拷貝給user
appl_ptr += frames; //讀地址加剛才拷貝的數據大小
if (appl_ptr >= runtime->boundary) //循環
appl_ptr -= runtime->boundary;
runtime->control->appl_ptr = appl_ptr;
if (substream->ops->ack) //這里沒有
substream->ops->ack(substream);
offset += frames; //偏移增加
size -= frames; //size減少
xfer += frames; //傳輸xfer增加
avail -= frames; //可讀的減少
2.單獨分析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)
//獲取buf的地址，這里off是偏移地址
char __user *buf = (char __user *) data + frames_to_bytes(runtime, off);
if (substream->ops->copy) //這里沒有
err = substream->ops->copy(substream, -1, hwoff, buf, frames)
else
char *hwbuf = runtime->dma_area + frames_to_bytes(runtime, hwoff); //獲取ring buf讀的地址
copy_to_user(buf, hwbuf, frames_to_bytes(runtime, frames)) //把dma的從hwbuf開始的數據拷貝到user，大小為frames