I spent the sunday reading some ALSA documentation and produced a replacement 
for sqUnixMIDI.c (which I compiled into Squeak by hacking the generated 
Makefiles, yuck), which compiles, and the three or so functions Scratch uses 
actually do something useful (I ignored MIDI input, the drumkit and other 
things). Maybe somebody with a better (read: any) understanding of the  squeak 
internals can use this as a basis to create something that actually works and 
is integrated into the build environment.

Some observations that should be adressed in a final version:

midiInit is only ever called when a note is played. So the MIDI output port 
will only come into existence when the first note has been sent, and only then 
can you connect the port to the input port of a sythesizer. This connection 
will be destroyed if you stop the script in Scratch (in sqMIDIClosePort), so 
you have to reconnect before starting the next script. There *must* be 
something better than that.

There is a slight mismatch between Squeaks sqMIDIGetPortCount and the ability 
to create as many ports as you want in ALSA.

The ALSA sequencer can schedule events, but the return type of 
snd_seq_queue_status_get_tick_time is (typedefed to) unsigned int, so I do not 
know if the assumption "The MIDI clock is assumed to wrap at or before half the 
maximum positive SmallInteger value. This allows events to be scheduled
into the future without overflowing into LargePositiveIntegers." holds. As far 
as I understand the ALSA documentation, the client shouldn't make these 
assumtion at all and refrain from guessing at future clock values: "As each 
sequencer queue has it's own clock the only way to deliver events at the right 
time is by using the relative timestamp format. When the event arrives at the 
queue it is normalised to absolute format." 
(http://www.alsa-project.org/alsa-doc/alsa-lib/seq.html)
My code is probably broken in this regard (Scratch produces only immediate events).

If you route the Squeak MIDI output to a sequencer that outputs to jack, Squeak 
may no longer be able to open the normal ALSA audio device, so you should 
either use a synth that does not require jack like timidity -iA -oS, or 
implement jack output for Squeak. The latter could be difficult, the former has 
the disadvantage of high latency (at least on my machine I have a noticable 
delay if I send events from an external keyboard to timidity).

Yours, Florian Hars.

PS: http://www.squeakvm.org/unix/ mentions something like "svn export 
http://squeakvm.org/svn/squeak/tags/unix-3.9-8", but that doesn't exist, there 
is no tag past unix-3.9-4 there.
-- 
But our moral language is fragmented; our contemporaries reject the Kantian
hunch that choosing those things most admirable and plausible as ends in
themselves is the best practice; autonomous sources of the good are everywhere
brown and broken. Thus we have PHP. http://lambda-the-ultimate.org/node/1463
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