Midi Merge Technique?

[Rob]

This timing message occurence thing has been an open question for a while,
and I *think* that it may be able to occur anywhere in the transmission,
otherwise the midi clocks would be all over the place, esp in a thick data
stream.
Only thing to do is to try it and see what happens.

Rob

----- Original Message -----
From: Fraser, Colin J <Colin.Fraser at scottishpower.plc.uk>
To: <synth-diy at mailhost.bpa.nl>
Sent: Friday, January 21, 2000 4:58 AM
Subject: RE: Midi Merge Technique?


> > -----Original Message-----
> > From: Byron G. Jacquot [mailto:thescum at surfree.com]
> > Sent: 21 January 2000 01:10
> > To: synth-diy at mailhost.bpa.nl
> > Subject: Re: Midi Merge Technique?
> >
> >
> > Just a quick clarification of terminology...I'm not as looped
> > as it might seem.
> >
> > By "message," I meant a complete "packet" of MIDI data, not
> > just a single
> > byte.  This could range from a 3-byte note on or off kinda
> > message, all the
> > way up to a file/sample dump via sysex.  (If we're only
> > parsing bytes, we
> > may as well just wire the 2 MIDI streams together with our
> > favourite logic
> > gate! ;> )
> -snip-
> > It might be wise to increase priority for system real-time
> > messages from the
> > input, as well.
>
> Coincidentally, I've been writing midi merge code over the last few days
to
> provide soft thru on my analogue sequencer.
>
> I use 3 FIFO buffers.
> One for data received via midi, one for data generated by the sequencer,
and
> one for the transmit buffer.
>
> A merge routine is called whenever data arrives in the rx or sequencer
> buffers (unless the tx buffer is not empty), and also after a tx complete
> interrupt.
> This routine checks if a complete message is ready to go from either
source,
> and then sends it (ie loads it into the tx buffer).
> The status byte for every message received is written into the rx buffer
> whether it is received or not.
> The transmit routine keeps track of the last status byte sent, and misses
> out unnecessary following status bytes.
> I could elaborate on this if anyone's interested.
>
> Anyway, there's a question I can't seem to find an answer to about the
midi
> spec.
> Maybe someone here knows...
>
> Is it legal for a system realtime message (F8, FA, FB, FC) to occur
*during*
> another message ?
>
> For example, can midi clock occur inside a note on ? ie  90,3C,F8,7F...
>
> The way I wrote the software on my sequencer and cv convertors, this is no
> problem, but other devices may not like it.
> Obviously, midi clock can only come from one source if two are being
merged,
> but if it can be inserted anywhere in the output stream, the merge process
> should not introduce any significant timing errors for synced devices - if
> system realtime is received, a flag can be set to tell the transmit
routine
> to resend the byte as soon as possible.
>
>
> Colin f
>
>
>
>
>
>