Subject: [linux-audio-dev] a few CoreAudio-related pointers
From: John Lazzaro (lazzaro_AT_CS.Berkeley.EDU)
Date: Wed Dec 12 2001 - 23:03:43 EET
Hi everyone,
With CoreAudio coming up on the list lately, I thought
I'd post two links that might clarify what (if anything) LAD
folks can learn from the implementation details. This brand
new document:
tells hardware folks how to write a device driver that
works for OS X. In the process, it shows how CoreAudio interconnects
with the kernel from the kernel side -- if you combine this document
with the earlier CoreAudio userland document, its pretty clear how
the whole system works.
A second difference under OS X it handles the equivalent
of our SCHED_FIFO. Basically, the highest priorities in OS X are
reserved for isochronous priorities -- you figure out the Mach
thread associated with your process or your Pthread, and you then
set the mach thread policy to be THREAD_TIME_CONSTRAINT_POLICY --
this policy is parameterized, you tell the OS about the periodicity
of your app and such, and the scheduler does its best to meet your
deadlines. The documentation for this is kinda murky right now,
if you look on the darwin-developer mailing list archives for a
set of posts starting on 8 Oct 2001 by Benjamin Golinvaux, and
followups by David A. Gatwood, and a more recent thread on
Coreaudio about mpg123 porting by David A. Gatwood, you can piece
together the Mach approach to real-time scheduling as implemented
in OS X.
This is posted just for "comparative systems" purposes --
it's not clear to me that these mechanisms are suitable for Linux
to use, but its always good to see how other people try to solve
a problem ...
--jl
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John Lazzaro -- Research Specialist -- CS Division -- EECS -- UC Berkeley
lazzaro [at] cs [dot] berkeley [dot] edu www.cs.berkeley.edu/~lazzaro
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