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== snd-usb-audio ==

Nevertheless, if you use a 2.4 kernel or can't use <code>[[udev]]</code> yet, ALSA's <code>snd-[[usb-audio]]</code> module has a feature that can solve your problems. As root, try this command:

<code>
 # modinfo snd-usb-audio
 filename:    /lib/modules/2.4.23/kernel/sound/usb/snd-usb-audio.o
 description: "USB Audio"
 author:      "Takashi Iwai <tiwai@suse.de>"
 license:     "GPL"
 parm:        index int array (min = 1, max = 8), description "Index value for the USB audio adapter."
 parm:        id string array (min = 1, max = 8), description "ID string for the USB audio adapter."
 parm:        enable int array (min = 1, max = 8), description "Enable USB audio adapter."
 parm:        vid int array (min = 1, max = 8), description "Vendor ID for the USB audio device."
 parm:        pid int array (min = 1, max = 8), description "Product ID for the USB audio device."
 parm:        nrpacks int, description "Max. number of packets per URB."
 parm:        async_unlink int, description "Use async unlink mode."
</code>

This module has several options, listed in lines starting with <code>parm:</code>. Index is a common option for every ALSA module, and it means the "card" order for your device. This is one of the key features we need. The other two are the <code>vid</code> and <code>pid</code>, meaning the Vendor and Product identifiers that  every USB device shows as descriptor attributes. You can obtain the numbers using the following command:

<code>
 # lsusb
 Bus 001 Device 004: ID 0763:1110 Midiman
 Bus 001 Device 003: ID 0582:0005 Roland Corp. Edirol UM-2 MIDI Adapter
</code>

The number 0763 is the Vendor ID for Midiman, and 0582 is the Vendor ID for Roland.  The numbers following the colon are the Product Ids for the Midisport2x2 (1110) and the UM-2 (0005) respectively. Be warned that the Midisport has a different product id before loading the firmware. We need the number after the renumeration, when it has the firmware loaded and running.

The next step is to assign an index number to every device driven by ALSA, not only the USB ones. This can be done on <code>/etc/modules.conf</code>, or <code>/etc/modprobe.conf</code>, depending on your Linux vendor and kernel version.

Suppose that we have two USB devices (Midisport2x2 and UM-2) one PCI card and we need also the [[virmidi]] driver. The ''card'' order will be the following:

#PCI card
#USB Midisport2x2
#USB UM-2
#Virmidi

The relevant lines in your <code>/etc/modules.conf</code> will be the following:

<code>
 alias snd-card-0 snd-via82xx
 alias snd-card-1 snd-usb-audio
 alias snd-card-2 snd-usb-audio
 alias snd-card-3 snd-virmidi
 options snd cards_limit=4
 options snd-via82xx index=0
 options snd-usb-audio index=1,2 vid=0x0763,0x0582 pid=0x1110,0x0005
 options snd-virmidi index=3 midi_devs=2
</code>

snd-[[via82xx]] is the ALSA module containing the driver for the PCI card. Assign it the <code>index=0</code> and it will be the first ALSA card in the system. That means: the PCM and raw MIDI devices will be named <code>hw:0,N</code>, and the sequencer client would have the number <code>64</code>, but in this case, my PCI card is a VIA VT8233/A/8235 without MIDI, so the sequencer client number 64 will be inexistent/unused.

There are two cards using the module snd-[[usb-audio]], and it has the assigned indexes 1 and 2. Notice the <code>vid</code> and <code>pid</code> parameters with the arguments for the Midisport2x2 and the UM-2. The three parameters are arrays, having up to eight comma separated elements. There should be the same number of elements for all parameters. Being the cards 1 and 2, the Midisport2x2 will be known as <code>hw:1</code> for the raw MIDI interface, and the UM-2 as <code>hw:2</code>. The sequencer client numbers will be 72 for the Midisport2x2 and 80 for the UM-2. These numbers will be the same in despite of the plug order, or the USB socket used. Even if you only plug the UM-2 but not the Midisport, the sequencer client for it will be 80 and the raw MIDI interface will be <code>hw:2</code>. 

NOTE: If you are using gentoo, you will need to run <code>modules-update</code> after modifying the files in <code>/etc/modules.d</code>.
 
Finally, we assign the persistent index 3 to the very useful [[virmidi]] (snd-virmidi) card. Use the following commands to verify your configuration:

<code>
 # amidi -l
 Device    Name
 hw:1,0,0  Midisport 2x2 MIDI 1
 hw:1,0,1  Midisport 2x2 MIDI 2
 hw:2,0,0  UM-2 MIDI 1
 hw:2,0,1  UM-2 MIDI 2
 hw:3,0    Virtual Raw MIDI (16 subdevices)
 hw:3,1    Virtual Raw MIDI (16 subdevices)
 
 # aconnect -ol
 client 72: 'Midisport 2x2' [type=kernel]
     0 'Midisport 2x2 MIDI 1'
     1 'Midisport 2x2 MIDI 2'
 client 80: 'UM-2' [type=kernel]
     0 'UM-2 MIDI 1     '
     1 'UM-2 MIDI 2     '
 client 88: 'Virtual Raw MIDI 3-0' [type=kernel]
     0 'VirMIDI 3-0     '
 client 89: 'Virtual Raw MIDI 3-1' [type=kernel]
     0 'VirMIDI 3-1     '
</code>