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From: sstreep@next.com (Sam Streeper)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: MIDI input problems (C or assembler programming)
Message-ID: <250@rosie.NeXT.COM>
Date: 6 Feb 91 19:26:36 GMT
References: <3901@ryn.mro4.dec.com>
Sender: news@NeXT.COM
Organization: Next Computer, Inc.
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In article <3901@ryn.mro4.dec.com> miskinis@aisg.enet.dec.com (John Miskinis) writes:
>
>	I hit the books, bought Mark Williams C, and wrote an interrupt
>routine that duplicates that the standard MIDI input code, but I write the
>bytes to MY buffer, and time-stamp each byte when it comes in.

You really must write your midi interrupt handler in assembler.  Fortunately
this handler is pretty simple.  The standard Atari interrupt handler is
actually pretty good, but you can optimize it slightly.  For an example
of the source to the standard handler, see the Abacus Internals book.
The default buffer is much too small (128 bytes, I think).  With a good
handler, a decent size buffer, and a good cable (most are crappy), you 
shouldn't lose any data.


>	This method allows application freedom, as MIDI input will happen in
>the background.  BUT I STILL LOSE DATA WHEN I MOVE THE MOUSE...

This is true and it sucks big time!  The problem here is that the 
keyboard/mouse ACIA and the midi ACIA interrupt at the same level to
the MFP 68901.  Also, the mouse packet parsing code is just too slow.
If you blast the midi port at full speed and move the mouse, its possible
that 2 midi characters will come in while you're parsing a mouse packet,
and BOOM! you lost the first one, since the hardware only buffers one
character.  The midi handler cannot preempt the (slow) mouse handler,
and this is a hardware architecture problem.

The solution of course is to rewrite the mouse/keyboard handler, which is
pretty difficult, especially if you want to maintain compatibility with
the way the OS expects to find things.  If you're writing a standalone
sequencer, this really isn't a problem, but for joe average it's difficult.

If you roll your own sequencer without the mouse handler, just _don't_move_
the_mouse_ (!) during critical times!  (1/2 8^))


I hope this helps...  Every profession sequencer writer has had to deal
with this.

-sam (sam_s@NeXT.com)