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TerryC65
Posts: 202
Joined: Sat May 09, 2015 7:50 am
Location: Wimborne, Dorset, UK

Conflicts when using a USB Hub and Audio Adaptors

Wed Jan 04, 2017 4:02 pm

Hi,

I've spent a significant part of the Christmas break trying to track down a problem using USB Audio Adaptors via a USB Hub to a Pi Zero. The Hub and the Adaptors were procured from ModMyPi so most of the initial discussion happened there because I suspected the hub or the Adaptors were causing the problem.

So. I have three USB Audio Adaptors, a WiFi Dongle, a mouse and a keyboard all plugged into the hub and the hub is then plugged into the Pi's data port. On boot up, the system invariably locked up. Sometimes, I could boot into the shell, but as soon as I tried to get into the desktop, the activity light on the first Adaptor in the tree flashed and then the mouse froze.

To cut a long story short, I eventually found that I could make this work if I plugged the Adaptors into three of the four ports on a Pi 2 or 3 (with the fourth used to connect the hub, which dealt with the rest). If I connected the hub and adaptors with the same configuration as the Zero (only the connection to the hub being used on the Pi), the fault was identical.

I've set usb_max_current=1 in config.txt and that made no difference. I understand that the Adaptors are USB V 1.1 or 1.2.

Has anyone any ideas how I could get this to work with the Zero? (We've just about spent the budget.)

aBUGSworstnightmare
Posts: 2069
Joined: Tue Jun 30, 2015 1:35 pm

Re: Conflicts when using a USB Hub and Audio Adaptors

Wed Jan 04, 2017 4:07 pm

what kind of 'audio adapters' are you using? Why do you need three of them?
Maybe all of them are reporting the same ID to the host ....
what's the output of

Code: Select all

lsusb

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TerryC65
Posts: 202
Joined: Sat May 09, 2015 7:50 am
Location: Wimborne, Dorset, UK

Re: Conflicts when using a USB Hub and Audio Adaptors

Wed Jan 04, 2017 4:15 pm

aBUGSworstnightmare wrote:what kind of 'audio adapters' are you using? Why do you need three of them?
Maybe all of them are reporting the same ID to the host ....
what's the output of

Code: Select all

lsusb
The adaptors are these https://www.modmypi.com/raspberry-pi/ac ... SB%20Audio

This project is to restore the bells in my local Model Town Minster and we want to be able to play mp3 files of organ music in the Chancel at the same time as we ring the bells in the Tower. So we need separate channels. I did explore grabbing the hdmi audio for one channel, but we're trying to reduce the spares holding.

Yes they do all report the same ID, but that has not prevented me accessing them (and playing mp3 files to them simultaneously) when I boot into the shell (I've had the occasional lock up in the shell too). It's only when I try to get into the desktop that they always lock up.

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TerryC65
Posts: 202
Joined: Sat May 09, 2015 7:50 am
Location: Wimborne, Dorset, UK

Re: Conflicts when using a USB Hub and Audio Adaptors

Thu Jan 05, 2017 9:47 am

A member of our local LUG spotted this https://www.raspberrypi.org/documentati ... md#support. If I've understood this correctly the Broadcom chip has a single USB port which has to carry all traffic. However, although the article only seems to apply to Models A and B, it seems to me that it is likely that the Pi Zero is likely to be wired in a similar way to the Model A and the PI 2 and the Pi 3 are similar to the Model B.

Since all of the traffic ends up at the single Broadcom port, then I can only see two possibilities as to why the Adaptors work when plugged directly into the native ports of a Pi 2 or 3 and don't when they are all funnelled through a single native port on any of these devices:
  • 1. The built in hub of the Model B, Pi 2 and Pi 3 somehow provides better power or data buffering.
  • 2. The Pi 2 and 3 are quad-core, so the CPU is not maxed out.
Does any of this seem feasible? Is there another explanation? If either of my assumptions are correct, then anything other a a multi-TT hub is unlikely to work with these Adaptors (and multi-TT hubs cost more than a Pi 3).

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TerryC65
Posts: 202
Joined: Sat May 09, 2015 7:50 am
Location: Wimborne, Dorset, UK

Re: Conflicts when using a USB Hub and Audio Adaptors

Thu Jan 05, 2017 3:04 pm

Answering myself again, there seems to be a third option (or maybe it's a subset of the first). I now think I understand a bit more about what is going on with these two situations, after a bit more help from my LUG. I tried to attach the outputs of 'lsusb -v' when the three devices are connected to a Pi 3 and to the Pi Zero, through the external Hub, but the BB software seemed to block this. They can be found at:

http://hadrian-way.co.uk/Misc/Pi3_lsusb-v.txt
http://hadrian-way.co.uk/Misc/Pi0_lsusb-v.txt

respectively.

Examining these shows that the bigger Pis both have one multi-TT port, whereas the Pi Zero only has single-TT ports.

Last question therefore; does anyone know of a multi-TT USB Hub that costs less than a Pi 3? All the ones I've found seem to be quite expensive.


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