26 Feb
2003
26 Feb
'03
11:50 a.m.
>any
>convincing (to me) arguments why an application should not handle
variable
sized
callbacks. VST process() is variable size I think as are EASI xfer
callbacks, but clearly JACK needs constant callbacks and there is nothing
I can do about that...
as i understand it, VST is only variable to allow for automation. And
if you follow the discussion here about XAP and elsewhere about PTAF,
you will see that many people consider this a mistake that comes from
not using "events" in the correct way. i feel that it should be the job of ALSA to handle
period sizes. if it
doesn't do a good job, it should be fixed. if we ask for a wakeup
every time 1024 frames are available,
I don't think an application should ask for a certain number of frames
to wakeup. The driver should dictate when to wake up. This is the way
my Audiowerk8 JACK driver works and it would get a lot more
complicated if I had to add support for user-space wake up at
arbitrary intervals.
and the interrupts occur at 420,
840 and 1260 frames, then we should be woken up on the third
interrupt, process 1024 frames of data, and go back to sleep.
This will not perform well since the available processing time per
sample will fluctuate.
the h/w
driver should handle this, not JACK. the latency behaviour will be
just as requested by the user.
IMHO JACK should be able to handle drivers that generate interrupts
with variable available frames by allowing non-const callbacks. There
is no way to only allow const callbacks without adding either large
latency or hurting performance for driver that don't generate interrupts
on available frames. It seems some soundcards, USB and possibly
FireWire audio are all better served with non-const callbacks. And
I still have not seen any convincing arguments that non-const callbacks
are a problem for JCAK client applications.
--ms