snd_pcm_ops的.pointer所實作的內容?

[stone886]

snd_pcm_ops的.pointer所實作的內容?
是在計算實際已傳出的資料嗎
我看datasheet沒有看到可以知道目前已傳輸的資料量
ACTL_PDST_LENGTH 0xB000_901C R/W DMA destination length register for
play
不知這個是不是

以下是我用來參考的代碼
static snd_pcm_uframes_t snd_nxc2600_pointer(struct snd_pcm_substream *substream)
{
struct audio_stream *stream = substream->private_data;
snd_pcm_sframes_t result;
result= bytes_to_frames(substream->runtime,
stream->buffer_pos+
stream->buffer_bytes-
nxc2600_dma_get_current_transfer_count(stream->chno,0));
);
return result;
}

[stone886]

是不是我沒電機背景才搞那麼久啊
呵呵

[独孤过儿]

我猜測你是想問.pointer這個實例出來的內容吧？

這種結構體的賦值方式是gcc的擴展或者是C99裏面的一個新的feature，具體是哪個我記不清楚了。可以直接給結

構體的某個成員賦值。

[morris88]

  pointer callback

   static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream *substream)
                                                                                

   This callback is called when the PCM middle layer inquires the current
   hardware position on the buffer. The position must be returned in frames,
   ranging from 0 to buffer_size - 1.

   This is called usually from the buffer-update routine in the pcm middle
   layer, which is invoked when snd_pcm_period_elapsed() is called in the
   interrupt routine. Then the pcm middle layer updates the position and
   calculates the available space, and wakes up the sleeping poll threads,
   etc.

   This callback is also atomic.

建议你先看看 src/Documentation/sound/alas/ 下面的文档，里面的内容很重要...

[puheavy123]

学习，帮顶。。。。。

[stone886]

那是不是每中斷一次,代表某一段資料量已被填滿嗎

[stone886]

[Quote=引用 3 楼 morris88 的回复:]
Perl codepointer callback

static snd_pcm_uframes_t snd_xxx_pointer(struct snd_pcm_substream*substream)


This callback is called when the PCM middle layer inquires the current
hardware position on the buffer.The position must be returned in frames,ranging from0to buffer_size-1.This is called usually from th…
[/Quote]
這些文件我都有看過了,所以我才會問datasheet沒有知道已傳輸量的問題

[morris88]

呵呵，貌似硬件不会来记录这个的，通常都是软件来完成的...