Re: Starting the device manually

[James Courtier-Dutton <James@superbug.co.uk>]

Eric Peters wrote:
> Dear all,
>
> I'm a bit confused by the alsa documentation. I want to fill up a buffer
> of a alsa device with snd_pcm_writei and then if the buffer is full, I
> want to be able to start the playback manually. By looking to the
> documentation, I found the method snd_pcm_sw_params_set_start_threshold.
> In some other messages on this list there was the hint to set this
> threshhold larger than the max_buffer_size and then the device shouldn't
> start automatically. So I've done. But unfortunately the playback starts
> again automatically. Here are the lines of code, I'm setting the
> buffer_size and period_size and the start threshhold:
>
>   
Why would you actually want to do what you describe. (You certainly can 
do it with ALSA, but as to why you would want to, is another thing entirely)
It is normally better to get the buffers running, sending silence 
samples to the buffer, and then introduce your sound when you want to.
One can accurately determine the delay or latency of the buffer, so 
accurately timing samples is not a problem.
One uses a callback approach to send sound to the card. A good example 
of this callback approach is an application called jackd.
http://jackaudio.org/

James


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