question about minimum latency. (jack) how to calculate it?

question about minimum latency. (jack) how to calculate it?

[Pierre-Laurent CHAMBERT]

Hi!

I would like to know how I can improve latency on digi32/8 driver.
The card has got a buffer of 128Ko, and block size per interrupt is 8Ko (so it 
makes 16 interrupt for the whole buffer). When I start jack I can use only 
setup 256 frame/periods (32bits, 8channel in adat mode) and 16 periods/
buffer. So this mean I can only have 80ms of latency?!? It's not possible to 
use less than 16 periods? 
I mean, a sound is recorded, the card send an interupt so the sound just 
recorded can not be read in the memory, and write back in memory 2 interrupts 
after? 
Maybe I miss something here, I already try to change number of periods/buffer 
in the driver, but of course with no luck.
So if the buffer size (128Ko here) and block size (8Ko) are always the same it 
cannot get a lower latency?

Thank you!

Pilo




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Re: question about minimum latency. (jack) how to calculate it?

[Takashi Iwai]

At Mon, 22 Nov 2004 07:15:02 +0100,
Pierre-Laurent CHAMBERT wrote:
> 
> Hi!
> 
> I would like to know how I can improve latency on digi32/8 driver.
> The card has got a buffer of 128Ko, and block size per interrupt is 8Ko (so it 
> makes 16 interrupt for the whole buffer). When I start jack I can use only 
> setup 256 frame/periods (32bits, 8channel in adat mode) and 16 periods/
> buffer. So this mean I can only have 80ms of latency?!? It's not possible to 
> use less than 16 periods? 
> I mean, a sound is recorded, the card send an interupt so the sound just 
> recorded can not be read in the memory, and write back in memory 2 interrupts 
> after? 
> Maybe I miss something here, I already try to change number of periods/buffer 
> in the driver, but of course with no luck.
> So if the buffer size (128Ko here) and block size (8Ko) are always the same it 
> cannot get a lower latency?

The latest CVS version of JACK includes my patch to improve the
latency on the cards like yours.  Please give a try.


Takashi


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