Subject: Re: [linux-audio-dev] rtlinux, MIDI timecode
From: Yann Orlarey (orlarey_AT_grame.fr)
Date: Thu May 04 2000 - 20:23:12 EEST
On Thu, 4 May 2000, Paul Barton-Davis wrote :
>As I've mentioned before, MIDI timecode seems very problematic for
>general purpose computers. Sending 2 bytes every 1.3 msec (for 30fps
>SMTPE) is just not something that Linux (or Windows, or MacOS) was
>really designed to make it easy to do.
MIDI timecode (MTC) requires only 2 bytes (MTC Quarter frame message : F1
nd) per quarter frame. Therefore, 30fps requires 2 bytes every 8.3 ms (not
every 1.3 ms). The reception of 8 Quarter Frame messages completely define
the SMPTE time every two frames.
Concerning performances, MIDI is very demanding in terms of interrupts. But
an old Mac II was able to deal with 2 full MIDI Thru + a 1 ms timer
interrupt (representing 2*2*3125 + 1000 = 13500 interrupts / second)
without problems.
-Yo-
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Yann Orlarey, (orlarey_AT_rd.grame.fr)
GRAME, 9 rue du Garet, BP 1185, 69202 Lyon, France
http://www.grame.fr
telephone : +33 (0)4 72 07 37 00, fax : +33 (0)4 72 07 37 01
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