[alsa-devel] Master Plan on rewinding

[Raymond Yau]

2014-9-13 下午6:43 於 "Alexander E. Patrakov" <patrakov at gmail.com> 寫道：
>
> 13.09.2014 14:57, Raymond Yau wrote:
>>
>>
>>  >>
>>  >>  >
>>  >>  > On my desktop PC, on snd-hda-intel with analog outputs for S16LE
>>  >> stereo, the granularity is 32 bytes (= 8 samples), and I get the
pointer
>>  >> granularity of 64 bytes (=16 samples) over HDMI. The minimum period
size
>>  >> is 32 samples in both cases.
>>  >>
>>  >> Do you mean hda-Intel does not support arbritray period size when you
>>  >> say the granularity is 32 bytes ?
>>  >>
>>  >> However the granularity of the emulated hda sound card inside any VM
>>  >> depend on the vm and the backend audio system and sound card
>>  >
>>  >
>>  > The precise meaning is defined here:
>>  >
>>  >
http://mailman.alsa-project.org/pipermail/alsa-devel/2014-May/076475.html
>>
>> Do you mean the different hda controllers may have different granularity
?
>
>
> Yes. My two hda controllers have different granularity.
>
>
>> Do your two hda controllers have different Fifo size ?
>
>
> If you mean the result of snd_pcm_hw_params_get_fifo_size(), then both
cards return 0. I call this function after snd_pcm_hw_params(), as
recommended by the documentation.

Do your hda controllers OSDnFIFOS register match the granularity ?

3.3.40 Offset 90:  {IOB}SDnFIFOS – Input/Output/Bidirectional Stream
Descriptor n FIFO Size

Length: 2 bytes

Table 39. Stream Descriptor n FIFO Size Bit Type Reset Description 15:0 RO
Imp.Dep

FIFO Size (FIFOS):  Indicates the maximum number of bytes that could be
fetched by the controller at one time.  This is the maximum number of bytes
that may have been DMA‟d into memory but not yet transmitted on the link,
and is also the maximum possible value that the LPIB count will increase by
at one time.  This number may be static to indicate a static buffer size,
or may change after the data format has been programmed if the controller
is able to vary its FIFO size based on the stream format.  If it is able to
change value after the data format has been programmed, the value update
must happen immediately before the next read of the FIFOS register, and
remain static until the next programming of data format.