Re: safe support for rewind in ALSA

[Raymond Yau <superquad.vortex2@gmail.com>]

2010/2/21 Kai Vehmanen <kvehmanen@eca.cx>

> Hi,
>
>
> On Mon, 15 Feb 2010, Raymond Yau wrote:
>
>  Even using a high resolution timer , the application still cannot achieve
>> latency better than the configured period size
>>
>> For USB case , the driver cannot give accurate hw pointer position , hw
>> pointer increase in steps for the current implementation, (i.e. the graph
>> is
>>
>
> ... but that's a real hardware limitation for the USB-driver, right? And
> even in the USB case, hw pointer is incremented in steps of URB transfer
> size, so even in this case, latency of a highres timer based application is
> not limited by the set period-size.
>
> Of course, there is no ALSA API to query the burst size (e.g. the
> granularity of hw_ptr updates), which is a real problem for generic apps
> (that are not hardcoded to work with just one ALSA driver).
>
>
The burst size is less than or equal to the minimum period size