[Jack-Devel] Cannot combine audio devices with more than 64 channels

[David Kastrup]

Jörg Müller <joerg.mueller7744 at gmail.com> writes:

> This is months old, but I have news to this topic.
>
> The suggested changes work and we have set up 11x16channel audio
> monitors. That is 176 speakers!
>
> However, running Jack is highly unstable, it crashes roughly every two
> minutes and causes a huge amount of XRuns even at buffer sizes like
> 16000. CPU is down at 5%, so that is not the issue. Jack runs without a
> problem when using just one card. However, we need to combine the three
> MADI-Cards via .asoundrc in order to eventually get to 768 channels.
>
> I have the jack logs here: https://pastebin.com/ke25cdXB
>
> Do you have any idea what could cause the issue?

768 channels is a whole lot of throughput.  The MADI cards work with
some bus mastering setup if I remember correctly, so the CPU load should
be a weak indication of how close you are to choking the system as long
jack is working efficiently: in that case the CPU load will be choked
_low_ when things go south.

So this looks like your next go-to area is the hardware.  Interrupt
priorities (rtirq), PCI burst lengths for the cards involved (make them
long enough to be efficient and short enough that the CPU can shovel the
stuff off to disk eventually).

Of course, you also _must_ make sure that the clocks of your converters
are _all_ hardware-synchronized or Jack has no chance to keep up with
both the slowest and fastest unit without eventually dropping samples on
the fast one.

-- 
David Kastrup