[LAD] timing the processing of queues between engine and ui threads?

Paul Davis paul at linuxaudiosystems.com
Sun Nov 6 13:10:33 UTC 2011

On Sun, Nov 6, 2011 at 2:20 AM, Emanuel Rumpf <xbran at web.de> wrote:
> 2011/11/5 Iain Duncan <iainduncanlists at gmail.com>:
>> On Thu, Nov 3, 2011 at 8:05 PM, David Robillard <d at drobilla.net> wrote:
>>> The only difference non-jack would make is you need some function to
>>> tell you roughly what audio time it is you can call from another thread.
>> Does one use the system clock for that?
> I think frame time (a frame of samples) is meant here  ? That time is
> delivered in the jackd process callback.
>> Is it accurate enough?
> Depends on the system clock used, I presume.
> For best accuracy, you have to configure your kernel to support HPET
> (high precision event) timers
> and make ALSA use it as default.

the clock used for the system clock is less important than using a DLL
to "link" the audio clock and the system clock. this enables you to
answer the question "if its time T on clock1, what time is it on

fons wrote the canonical paper on this for a Linux Audio conference a
few years ago, and JACK contains a DLL for this purpose
(jack_get_microseconds() will return a prediction of the current time
according to the audio clock, based on the system clock and the DLL.

More information about the Linux-audio-dev mailing list