[LAU] Motu 1248 - Full success

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Mon May 15 06:17:49 UTC 2017

On 05/13/2017 03:38 PM, Moshe Werner wrote:
> On Fri, May 12, 2017 at 10:03 PM, Fernando Lopez-Lezcano
> <nando at ccrma.stanford.edu <mailto:nando at ccrma.stanford.edu>> wrote:
>     I have never had the time to try to make the whole AVB thing work.
>     Trying OpenAVB a while back I managed to get the Motu to sync with
>     the Linux box through AVB, but never went as far as getting
>     discovery and streaming working (no time). You do need an ethernet
>     interface that has AVB support (Intel i210, for example).
>     On the other hand I'm working on a big system that uses (for now)
>     USB at 44.1/48 with a 64 channel count to interface with computers,
>     and then the rest of the I/O going through AVB streams to and from
>     additional boxes (I use either an A16 or 24ai as entry points
>     because they support 8 i/o AVB streams). Pretty neat with all the
>     routing matrices shuttling samples back and forth. You have to pay
>     attention to how many AVB streams each card can handle (they are not
>     necessarily symmetric).
> That's great news that AVB is working on linux too!

Nope, sorry, not yet. Probably doable but I do not know. As I said, I 
managed to get linux to see a Motu device - the clock, that is - and 
sync to it (or the other way around, I don't remember). I did not do 
discovery and streaming... maybe the existing free software could do 
that if programmed correctly, I don't know (only 24 hours in each day).

> Could you elaborate on the connection scheme of your setup? Are the
> different Motu boxes connected via the AVB switches?

The Motu boxes are connected through a Motu AVB switch and AVB streams. 
As I do not have OpenAVB working (yet), the connections to and from 
Linux are done through USB2. In all cases the main control machine is 
connected to a 16A and auxiliary computers through the 24ai (because of 
AVB stream count). Everything else connects through the internal routing 
matrix and AVB streams, very flexible. All devices slave to one over 
AVB. Input and output not to the computer are handled through analog 
and/or ADAT I/O.

As the channel count is high 64 channels is a must - I had discarded the 
Motu devices because they were limited to 24 channels I/O but then they 
issued a firmware update that enabled a configurable tradeof between max 
sampling rate and number of channels over USB2. I was looking at a 
solution using MADI before, but this was more flexible and cheaper 
(limited budgets), but of course very vendor specific. I have 
(currently) three use cases for this setup, one is using this as the 
core I/O for the GRAIL, our "portable" 3D surround speaker concert 
system - tested in two concerts so far. Another is for the control 
system of an ongoing upgrade for our concert hall (the Stage) from 16.8 
to 48.8 (this is the one that forced me to find a solution). I'm also 
testing this to replace the existing audio I/O for our Listening Room 
(just testing this last Friday, looks like may be able to run this at 
64x2 instead of the current 128x2 with RME and MADI / RayDAT cards).

So far so good... hopefully I will not run into any pitfalls :-)

>     I had problems with the newer generation of Motu cards that have a
>     USB3 interface, so beware. Those work fine with USB2 connections but
>     then the I/O is restricted to 24 channels input and output (in the
>     older generation and with the latest firmware you can select whether
>     you have more channels and less sampling rate options or visceversa
>     - that is not available in these new cards). If you connect to an
>     USB3 port the USB subsystem in the kernel hangs or gets really
>     confused. Reboot time :-(
> That's not so great news:(
> Why get it right just to do it all wrong again...?

I currently do not believe this is a problem with their interface, looks 
more likely to be a kernel problem in Linux (but I could be wrong).

-- Fernando

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