Re: Event Based time synchronization with ALSA

[Paolo Losi <p.losi@hypersonic.it>]

Hi Benno,

	thank you very much for you response.
	
Benno Senoner wrote:
  > The above routine has the advantage that you can use any kind of
> periodsize (fragment size) in ALSA
> and the send_rtp packet() always gets 20msec worth of data.
> But you must ensure that the ALSA period size must be <20msec , 
> otherwise too much jitter is introduced.

I see your point.... but I would have two objections:
- I don't want/can't use threads
- I get too much jitter

If I make poll timeout every 20ms in the main loop,
I'm sure I get 20ms worth of data
so I can busy loop to reading (in blocking mode) all samples
(If I would want to enforced that period is power of two, I could
choose the max power of two number of samples that is divider of the 
required number of samples)
That would be 8000HZ sampling for 20ms => 160 sample per packet
=> 5 32samples reads

But I'd rather tell ALSA: "please wake up poll as soon as you have
160 samples available". Is that feaseble? Can I expect to be always
woken up?

How

snd_pcm_sw_params_set_avail_min
snd_pcm_sw_params_set_sleep_min
snd_pcm_sw_params_set_start_threshold  	

relates to my problem?

I tried to read the API doc but, since I've no experience with audio
programming, I didn't get all the points...

Can anyone point to a good poll based read example?

	thanks again benno!

	Paolo


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