Subject: Re: [linux-audio-dev] priority inversion & inheritance
From: Paul Davis (pbd_AT_op.net)
Date: Thu Jul 11 2002 - 14:43:29 EEST
>> What hardware? You\'ve mentioned this quite a few times on jackit-devel,
>> but so far without examples. D/A or D/A hardware always runs at a constant
>> speed (at least I haven\'t heard about variable rate sampling).
>
>This is not true. There is hardware that runs with variable sample rate. This
>can be used for sync to tape. (The hardware I know that supports this does
>generate interrupts on a constant number of samples though)
exactly, even though SR varies, nframes stays constant. so this case
is not an issue.
>> Either the
>> software continuously polls the audio hw buffers (not really an option) or
>> is waken up periodically using interrupts.
>
>There is hardware that just interrupts at a constant rate. With this hardware
>the frames that or ready isn\'t exactly constant. You might assume some value,
>but if it isn\'t exactly correct then you\'ll drift.
can you give us a name? i know about the ymfpci and the korg
interfaces. they interrupt at a constant rate, and they are both
broken in other ways. neither design is still in production, AFAIK,
and i would guess that part of this is that they realized what an
unbelievably stupid design they had come up with.
>think it is wrong to have the driver export an interface that is not used
>by the hardware.
agreed. however, i might be in favor of simply not supporting such
hardware. this is what happens with ASIO, for example. there are no
ASIO drivers for several audio interfaces, and there never will be. i
don't think its unreasonable to say "this hardware is not designed in
a way that is conducive to full duplex low latency audio, and so it
can't be used with JACK".
>And besides that, I\'m pretty sure there is hardware that doesn\'t
>use power of 2 sized periods. Should that be a requirment too?
there is nothing about power-of-2 in the JACK API.
--p
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