Re: Naming two identical USB devices (need help)

["Ingo Müller" <alsa@ingomueller.net>]

Hi!

I thought about your problem again and I think I made a small progress!
I was able to set the cards number to any number I want using a udev
rule, so I could use that card with plughw:n,0 where n was the number of
my choise. I didn't use a udev rule that makes a lot of sense, but I'm
sure that there is a possibility to create a rule that depends on the
usb port your usb sound card is plugged in. Here is what I did:

I looked at the devices that where created before I did anything:

ingo@ingo-desktop:~$ls -l /dev/snd/
insgesamt 0
crw-rw---- 1 root audio 116, 11 2007-02-10 18:26 controlC0
crw-rw---- 1 root audio 116,  3 2007-02-10 18:26 hwC0D0
crw-rw---- 1 root audio 116, 13 2007-02-10 18:26 hwC0D2
crw-rw---- 1 root audio 116,  4 2007-02-10 18:26 midiC0D0
crw-rw---- 1 root audio 116, 14 2007-02-10 18:26 midiC0D1
crw-rw---- 1 root audio 116, 15 2007-02-10 18:26 midiC0D2
crw-rw---- 1 root audio 116, 10 2007-02-10 18:26 pcmC0D0c
crw-rw---- 1 root audio 116,  9 2007-02-10 18:26 pcmC0D0p
crw-rw---- 1 root audio 116,  8 2007-02-10 18:26 pcmC0D1c
crw-rw---- 1 root audio 116,  7 2007-02-10 18:26 pcmC0D2c
crw-rw---- 1 root audio 116,  6 2007-02-10 18:26 pcmC0D2p
crw-rw---- 1 root audio 116,  5 2007-02-10 18:26 pcmC0D3p
crw-rw---- 1 root audio 116, 12 2007-02-10 18:26 seq
crw-rw---- 1 root audio 116,  2 2007-02-10 18:26 timer

The I looked at the udev rules, that created these devices (in
/etc/udev/rules.d/20-names.rules):

# Sound devices, group under /dev/snd
KERNEL=="controlC[0-9]*",		NAME="snd/%k"
KERNEL=="hwC[D0-9]*",			NAME="snd/%k"
KERNEL=="midiC[D0-9]*",			NAME="snd/%k"
KERNEL=="pcmC[D0-9cp]*",		NAME="snd/%k"
KERNEL=="seq",				NAME="snd/%k"
KERNEL=="timer",			NAME="snd/%k"

These rules only "move" the sound devices to the snd/ directory. In
order to change the name of the created devices, I created a rule for
every device that has been created before, using its name from the first
ls command, and changed the card number (still moving it to snd/), here
it is number 3.

KERNEL=="controlC0",		NAME="snd/controlC3"
KERNEL=="hwC0D0",		NAME="snd/hwC3D0"
KERNEL=="hwC0D2",		NAME="snd/hwC3D2"
KERNEL=="midiC0D0",		NAME="snd/midiC3D0"
KERNEL=="midiC0D1",		NAME="snd/midiC3D1"
KERNEL=="midiC0D2",		NAME="snd/midiC3D2"
KERNEL=="pcmC0D0c",		NAME="snd/pcmC3D0c"
KERNEL=="pcmC0D0p",		NAME="snd/pcmC3D0p"
KERNEL=="pcmC0D1c",		NAME="snd/pcmC3D1c"
KERNEL=="pcmC0D2c",		NAME="snd/pcmC3D2c"
KERNEL=="pcmC0D2p",		NAME="snd/pcmC3D2p"
KERNEL=="pcmC0D3p",		NAME="snd/pcmC3D3p"

The result: My card was not card 0 anymore ("Karte 0"), but card 3
("Karte 3") and I was able to use it with plughw:3,0.

ingo@ingo-desktop:~$aplay -l
**** Liste von PLAYBACK Geräten ****
Karte 3: Live [SBLive! Platinum [CT4760P]], Gerät 0: emu10k1 [ADC
Capture/Standard PCM Playback]
  Untergeordnete Geräte: 32/32
  Untergeordnetes Gerät '0: subdevice #0
  Untergeordnetes Gerät '1: subdevice #1
  Untergeordnetes Gerät '2: subdevice #2
  Untergeordnetes Gerät '3: subdevice #3
...

That means that there is a way to influence the number of the card with
udev! Now, everything you have to do is find a udev rule that matches a
certain usb port. As you can run external programs with udev, there must
be a way to do that.

I'm going to play with udev now, too, so if I find something, I'll tell
you. In return, it would be awesome if you could write down - even it is
only short - a howto about how to manage two identical devices, once we
got it working.

Regards, Ingo



Jean-Michel Pouré schrieb:
> Hello,
> 
> My need is very basic.
> 
> I am using two Terratec Aureon USB MK2 devices.
> But this could be any case where two devices are the same.
> 
> My question is:
> 
> Is there a way to make sure that each physical device always has the
> same name: plughw:0,0 (first identical card) and plughw:1,0 (second
> identical card). This would allow me to plug the cards and forget the
> plugs. 
> 
> Presently, numbers change on every reboot or if I hotplug devices.
> 
> I read on the wiki that it was possible to load modules in a precise
> order. But it seems to be working in case of several ***different***
> devices, not several identical devices:
> http://alsa.opensrc.org/MultipleCards
> 
> Any idea? Is there a way to use Udev?
> 
> If it is not possible in the current state of Alsa, I will send back one
> device to the retailer, in which case I need your kind advice quickly.
> 
> Kind regards,
> Jean-Michel Pouré


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