[gmpi] Re: Topic 6: Time representation
- From: Paul Davis <paul@xxxxxxxxxxxxxxxxxxxxx>
- To: gmpi@xxxxxxxxxxxxx
- Date: Fri, 09 May 2003 13:33:19 -0400
>Well ... upto now, people understood very well that the reaction rate of
>their system was depending on the buffering...
who understood this? why did they think that? anyone who thought this
was, i'm afraid, the victim of short-cut software design and/or bad
advice. its simply not true.
> So why going into the
>opposite way !? Especially when you know how it's difficult to handle and
>synchronise different data stream on non real-time O/S like windows / Linus
>/ OSX.
its tricky, but no more tricky than most audio (host) programming.
>Just an example : the time of a MIDI event coming from a serial device
>cannot be fixed with less than 1ms of precision (just because 1ms is the
>time to transmit 3 bytes à 32000 bauds so one regular MIDI event - note that
you can timestamp each individual byte, and the overall message, if
you choose to do so. there are a few significant single byte MIDI
message (MIDI clock, for example), and several 2 byte messages. their
time of arrival is very well-defined.
>3ms is the time to communicate a 3 note chord) . add to this 1ms the event
>handling of the O/S and the higher priority process and explain me how you
i can timestamp MIDI data on my linux system to within about 5 usec of
its arrival at the interface, assuming that interface interrupts the
CPU promptly. with the latest linux kernel (or a patch to 2.4), i can
schedule its delivery to without about 10 usec of a given UST
time. from what i read, OS X is about as good, or better.
--p
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