[linux-audio-dev] Basic MIDI question

Jens M Andreasen jens.andreasen at chello.se
Mon Jul 24 23:33:11 UTC 2006

On Mon, 2006-07-24 at 19:28 -0400, Lee Revell wrote:
> On Tue, 2006-07-25 at 01:19 +0200, Jens M Andreasen wrote:
> > On Mon, 2006-07-24 at 17:55 -0400, Lee Revell wrote:
> > 
> > > Ugh.  All I need to do is snoop note on, note off, and the note number.
> > > But you're saying that 0x81 is sometimes part of a timestamp, and other
> > > times it means note off on channel 1?
> > > 
> > > So you are saying my driver needs to have full knowledge of the MIDI
> > > state machine in order to snoop note on and note off?
> > > 
> > Driver? This is a driver for a midi-port on a sound-card or a some kind
> > of midi-file player?
> It's similar to a driver for a MIDI port on a sound card, except the
> driver additionally has to respond to note on and note off by twiddling
> some other bits in the hardware.  It's equivalent to having to flash an
> LED for note on and another for note off.
> I wrote the driver as an ALSA rawmidi device, which was probably not the
> best idea - I did not realize at the time that I would have to interpret
> the MIDI stream.  An ALSA kernel sequencer client would have been more
> appropriate.

Confused again here. There are no delta-times in the midi-stream. You
mean: " ...  have to interpret the midi *file*"

> I think I can get away with always treating 0x90 as note on and 0x80 as
> note off regardless of the context.
> (I can't release source or give the hardware details now, as the
> hardware is still being developed)
> Lee

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