Re: Click after draining

[Giuliano Pochini <pochini@shiny.it>]

On 19-Oct-2004 Takashi Iwai wrote:

>> >> > The period size is always same even for the last period, AFAIK.
>> >>
>> >> Only if the driver explicitly asks for it by calling
>> >> snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS).
>> >
>> > No, this means that buffer_size = N * period_size, where N is
>> > integer.  Without this constraint, N doesn't have to be an integer.
>>
>> Yes, exactly. If N isn't integer, the buffer is formed by
>> bufsize\persize periods (== the integer part of N) plus one
>> short period which is bufsize%persize long.
>
> The period size is constant regardless of N because it simply defines
> the interval of interrupts.  When N isn't integer (say, 2.5), the
> transfer point moves like:
>
>       0, 1, 2, 0.5, 1.5, 0, 1, ...
>
> That is, when the point is at 2, the transfer is split to two parts
> (2-2.5 and 0-0.5).

Currently my driver uses a short period. To fix it the
driver should use a special feature of the DSP that allows
the driver to build the s-g list on the fly. It also has
the bonus that the DSP automatically stops the trasport
when it reaches the last programmed period, so draining
and xruns stop exactly where expected. It's more complex
than the current ring buffer implementation.

Out of curiosity, is there any driver that supports
non-integer N ?  And why everything works fine even if the
driver uses unequal periods ?  It should skip all the time.

Anyway, _fill_silence() can still overflow.


--
Giuliano.


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