On Sat, 12 Oct 2002, James Courtier-Dutton wrote:
> Currently, the state of play is that "snd_pcm_hw_params_can_pause ()"
> should not be called until one has first done the first
> "snd_pcm_hw_params()"
>
> I start with
> snd_pcm_hw_params_any(this->audio_fd, params);
> then go about setting params, e.g.
> snd_pcm_hw_params_set_access()
> snd_pcm_hw_params_set_format()
> etc.
> Then
> snd_pcm_hw_params()
> then
> snd_pcm_hw_params_can_pause (params)
>
> If the "snd_pcm_hw_params_can_pause (params)" goes before the
> "snd_pcm_hw_params()" an invalid result is returned. I.E. the result is
> always 1 even for cards which don't support it.
>
> I think the documentation should make it clear when one should use
> "snd_pcm_hw_params_can_pause ()".
> or maybe "snd_pcm_hw_params_any()" should be modified to correctly fill
> the "can_pause" bit.
> Maybe I have missunderstood the API, but I would prefer the approach of
> first retrieving the current hw params, then go about modifying it, then
> writting it back. If one has not set any hw params yet, it would fill
But what's "current configuration"? What you want to prefer? rate?
channels? period_size? No, application should give these hints to driver.
> the structure with the most general case, then allow the application to
> set params to further restrict the config.
> I had assumed that "snd_pcm_hw_params_any()" did the retrieving of the
> current hw params, but reset to the least restrictive settings. I don't
> think "can_pause" is anything an application can set, the hardware on
> the card decides that, so the "snd_pcm_hw_params_any()" should cause
> "can_pause" to return a valid setting that matches the hardware, instead
> of having to wait for the params to be written to the card with
> "snd_pcm_hw_params()" before "can_pause" is set accurately.
All these functions needs exactly one configuration at input.
The snd_pcm_hw_params() function chooses one configuration and sets it to
hardware. I've updated documentation.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project http://www.alsa-project.org
SuSE Linux http://www.suse.com
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