20 Feb
2018
20 Feb
'18
1:04 a.m.
JACK is already much closer to the hardware than the networking stack.
At the conclusion of the jack process callback, it writes samples *directly
into the memory mapped buffer being used by the audio hardware*. The
process callback is preemptively (and with realtime scheduling) triggered
directly from the interrupt handler of the audio interface.
JACK does not use a round-robin approach to its clients. It creates a data
(flow) graph based on their interconnections and executes them (serially or
in parallel) in the order dictated by the graph.
On Mon, Feb 19, 2018 at 5:57 PM, Jonathan Brickman <jeb(a)ponderworthy.com>
wrote:
Not really sure the subgraph is so good -- one of the
things JACK gives us
is the extremely solid knowledge of what it just did, is doing now, and
will do next period. If I run Pulse with JACK, it's JACK controlling the
hardware and Pulse feeding into it, not the other way around, because Pulse
is not tightly synchronized, whereas JACK is. But if you can make it work
as well, more power to you.
Concerning seeking and timing, though, I have had to wonder. My
impression of JACK for a long time (and more learned ladies and gentlemen,
please correct) is that it uses a basically round-robin approach to its
clients, with variation. I have had to wonder, especially given my need
for this <https://github.com/ponderworthy/MultiJACK>, how practical a
model might be possible, using preemptive multitasking or even
Ethernet-style collision avoidance through entropic data, at current CPU
speeds. It's chopped into frames, right? Couldn't audio and MIDI data be
mapped into networking frames and then thrown around using the kernel
networking stack? The timestamps are there...the connectivity is
there...have to do interesting translations... :-) Could be done at the IP
level or even lower I would think. The lower you go, the more power you
get, because you're closer to the kernel at every step.
--
*Jonathan E. Brickman jeb(a)ponderworthy.com
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