Subject: Re: [linux-audio-dev] midi events in jack callback (was: Reborn)
From: Tim Goetze (tim_AT_quitte.de)
Date: Fri Aug 16 2002 - 19:57:13 EEST
Paul Davis wrote:
>>I find that for sending MIDI to an external device, "resolution = RTC
>>Hz" works very well. It is a problem that a realtime audio thread
>>'suffocates' a RTC thread if low-latency is required, and only one
>>processor available. It's very hard to find a clean solution in this
>
>why not just run the RTC thread at a higher priority? or does that
>cause other problems?
The problem is I write(2) MIDI from within the RTC thread; with the
drivers/hardware we have I see no other way to ensure the bandwidth
is used optimally and that MIDI clock is precise. (Sidenote:) That's
also why I think firm timers don't help much; CC/pitch bursts must be
fed to the interface that way, not to think of sysex.
When writing to MIDI ports, some (especially the cheap) interfaces
will block in kernel for generous amounts of time. Poll(2)ing for
a write possible condition is not an option, on the AWE for example
this can give up to 30% constant load in kernel. Ouch.
For these reasons, I haven't yet seriously thought of running the RTC
thread at a higher priority, though now I think maybe my stance should
be reevaluated?
tim
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