[Jack-Devel] AVB Backend and MIDI question

Christoph Kuhr christoph.kuhr at web.de
Mon Jun 24 13:46:12 CEST 2019


> As a side question regarding Jack2 and midi: I would like to use jack's
> midi mechanism to pass control information between components in my
> automation system. So far I have been able to twist existing midi
> packets suck as time-code, and such to control player components and
> keep my mixer appraised as to source play positions and such. However, I
> have no easy way to pass meta data, such as song tags, through midi,
> with out the complexity of using sysex messages and base64 encoding the
> 8 bit meta-data fto be passed as midi data. Can I ignore midi's
> underlying byte format and just pass 8 bit buffers to jack and expect
> jack to deliver the buffers with out jack inspecting the buffers for
> validity according to midi? I only intend to use the midi ports within
> my applications various player and encoder components. I do not expect
> any of this data to actually be send to a device or program that is
> expecting real midi data.

  in the AVB realm, you would use AVDECC AEM for such a purpose instead
of abusing MIDI for it. ;-)

I did not look at JACKs meta data API, but I suppose it could be
integrated with AEM very nicely...

>>> I am not clear how one goes about setting up which
>>> device on the network is the clock master
>> If you have access to IEEE specs see IEEE 1588-2008 and IEEE 802.1AS.
>> 802.1AS is a profile of 1588-2008, there is what is known as "best master
>> clock algorithm" to select the best clock.  If multiple devices are
>> advertising equivalent quality ranking there is a tie breaker, I think
>> based on MAC address, but don't  quote that, I am going from memory and
>> have not looked at the details in quite a while.

As mentioned BMCA takescare of it. It is a nice feature to be able to
choose the GM, but it practically makes no sense.
What is the need for a specific GM if you AVB switch is down?
Thus, one of the AVB switches involved should be the GM. The "core-most"
switch in particular.

Or  can someone think of a scenario, where this does not make sense?


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