[PD-dev] [pure-data:bugs] #1272 midiout not working correctly on ALSA

Albert Graef aggraef at gmail.com
Sun Oct 16 20:08:05 CEST 2016

Hi Giulio,

no, AFAICT that's not the way ALSA works. I haven't really looked in the
ALSA code, but it seems that assembling the MIDI messages has to be done
using the corresponding sequencer API calls. There might be some drivers
which handle this, but I never had this working properly when outputting
sysex using either internal ALSA connections or external MIDI gear via a
USB-MIDI device.

All I can say is that the suggested patch seems to be the right way to do
this (those API calls are there for a reason), and that it works for me
with every MIDI equipment I tried it with.


On Sun, Oct 16, 2016 at 7:25 PM, Giulio Moro via Pd-dev <pd-dev at lists.iem.at
> wrote:

> Out of curiosity, is it not up to the receiving device to parse the
> received bytes in such a way that they form a coherent message? Or is there
> a "timeout" after which a sysex message is considered aborted ?
> I don't remember the latter from the specs, so I always assumed the former.
> Giulio
> ------------------------------
> *From:* Albert Graef <agraef at users.sf.net>
> *To:* pd-dev at lists.iem.at
> *Sent:* Sunday, 16 October 2016, 18:17
> *Subject:* [PD-dev] [pure-data:bugs] #1272 midiout not working correctly
> on ALSA
> ------------------------------
> * [bugs:#1272] <https://sourceforge.net/p/pure-data/bugs/1272/> midiout
> not working correctly on ALSA*
> *Status:* open
> *Group:* v0.47
> *Created:* Sun Oct 16, 2016 05:17 PM UTC by Albert Graef
> *Last Updated:* Sun Oct 16, 2016 05:17 PM UTC
> *Owner:* Miller Puckette
> This has been there forever, and affects all Linux systems when using ALSA
> MIDI devices.
> sys_alsa_putmidibyte() in s_midi_alsa.c outputs individual bytes instead
> of complete MIDI messages. You can clearly see this, e.g., when sending a
> sysex message from Pd to an ALSA MIDI output and looking at the results in
> kmidimon. Instead of a proper sysex message you'll get a sequence of
> (malformed) single-byte messages.
> You can't just output single bytes of a multi-byte MIDI message with
> snd_seq_event_output_direct(), this only works with single-byte (such as
> system realtime) messages. The proper way to do this, so that it works with
> any MIDI message, is to use snd_midi_event_encode_byte() and output the
> message when it's complete. The following fix is from the pd-l2ork repo,
> but it should apply cleanly on the current pure-data master branch:
> https://github.com/pd-l2ork/pd/commit/9f5a265
> ------------------------------
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Dr. Albert Gr"af
Computer Music Research Group, JGU Mainz, Germany
Email:  aggraef at gmail.com
WWW:    https://plus.google.com/+AlbertGraef
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