what is trigger time?

what is trigger time?

[Hanbiao Wang]

Hi, All
    According to the ALSA documentation, the following two functions
snd_pcm_status_get_trigger_tstamp()
snd_pcm_status_get_trigger_htstamp()
are suppose to get the "trigger time". However, I can not find any
documents that explains or define the meaning of the "trigger time".
Is that the time when a whole period of samples in the buffer is ready to
be read in? Could somebody please give me a hint? Thanks a lot.

Hanbiao


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Re: what is trigger time?

[Lee Revell]

On Thu, 2004-10-07 at 21:07, Hanbiao Wang wrote:
> Hi, All
>     According to the ALSA documentation, the following two functions
> snd_pcm_status_get_trigger_tstamp()
> snd_pcm_status_get_trigger_htstamp()
> are suppose to get the "trigger time". However, I can not find any
> documents that explains or define the meaning of the "trigger time".
> Is that the time when a whole period of samples in the buffer is ready to
> be read in? Could somebody please give me a hint? Thanks a lot.
> 

I don't have the source in front of me but I would expect this to be the
time when the ALSA middle layer executed the trigger callback.  This
happens when a PCM is stopped, started, or paused.

Lee



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Re: what is trigger time?

[Hanbiao Wang]

On Fri, 8 Oct 2004, Lee Revell wrote:

> On Thu, 2004-10-07 at 21:07, Hanbiao Wang wrote:
> > Hi, All
> >     According to the ALSA documentation, the following two functions
> > snd_pcm_status_get_trigger_tstamp()
> > snd_pcm_status_get_trigger_htstamp()
> > are suppose to get the "trigger time". However, I can not find any
> > documents that explains or define the meaning of the "trigger time".
> > Is that the time when a whole period of samples in the buffer is ready to
> > be read in? Could somebody please give me a hint? Thanks a lot.
> >
>
> I don't have the source in front of me but I would expect this to be the
> time when the ALSA middle layer executed the trigger callback.  This
> happens when a PCM is stopped, started, or paused.
>
> Lee

   Thanks for Lee's answer. Other than start, stop, pause of PCM, are
there any other events that could be regarded as triggered?

After I started a PCM for capture, I immediately examined the trigger time
by calling snd_pcm_status_get_trigger_tstamp(). Then I read data by
calling snd_pcm_readi(). After that I examine the trigger time again by
calling the same snd_pcm_status_get_trigger_tstamp(). However, these two
trigger time has a difference of 1108542 us. The first trigger time could
be the start of PCM, I really have no clue of what the second trigger time
corresponds to. Please enlighten me on this issue. Thanks a lot in
advance.

Hanbiao


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