MIDI transport inoperable -- Behringer UFX1204

[John C. <joh...@gm...>]

I am having an unresolved issue with the MIDI transport control
section of the Behringer UFX series mixer. [UFX1204]


This device is equipped with two interfaces. Firewire and USB.  It is
both an audio interface and a MIDI control surface.

I am using the most recent kernel:
---
Linux w530 4.6.2-hz1000-rt3 #3 SMP PREEMPT RT Thu Jun 23 11:41:06 CEST
2016 x86_64 GNU/Linux

Accessing the device uses the following modules:
---
snd_firewire_lib       32768  1 snd_bebob
snd_rawmidi            32768  4
snd_firewire_lib,snd_bebob,snd_usbmidi_lib,snd_seq_midi
snd_pcm               106496  9
snd_firewire_lib,snd_pcm_oss,snd_usb_audio,snd_bebob,snd_hda_codec,snd_hda_intel,snd_hda_core
firewire_ohci          40960  0
firewire_core          65536  3 snd_firewire_lib,snd_bebob,firewire_ohci
crc_itu_t              16384  1 firewire_core


USB MIDI interface to-and-from the transport section of the device
works flawlessly.

>From the same application software Firewire MIDI communication to the
device drops messages.

I have read that MIDI section of the linux Firewire stack is not
respecting the protocol rate limit. ref:
http://mailman.alsa-project.org/pipermail/alsa-devel/2014-April/075912.html
---
2.Data rate for MIDI substream
With current implementation, the maximum data rate for MIDI substream in
out-stream is one eighth of sampling rate. For example, at 48.0kHz, it's
6,000 bytes. This is excess over standard MIDI data rate, 3,125 bits per
second. So a few devices can have buffer over flow when receiving much
MIDI messages. For example, M-Audio Firewire 1814 transmits packets with
discontinuity in this case. I guess that Fireworks based devices and
some BeBoB based devices ignore MIDI messages in more than 8 data blocks
of packets and this is vendor's effort for this issue.
Drivers need a throttle for this issue but this is for future work.
---

Conversely, the Firewire release notes say:
https://ieee1394.wiki.kernel.org/index.php/Release_Notes/3.x#Linux_3.19
---
snd-firewire-lib
.       Limit MIDI transmission rate as per specification to prevent
loss of messages.
---


So I'm left to wonder what the actual status of the Firewire MIDI
substream protocol is, as the behavior I see, dropped packets sent to
the UFX1204, is consistent with data overruns. I am assuming that the
message content is correct as the MIDI transport functions correctly
when accessed via the USB interface.

Should I expect this to work, or is this a known open issue?

Thanks
jCandlish
.

This inquiry was originally posted here:
https://linuxmusicians.com/viewtopic.php?f=6&p=72314#p72314