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I have noticed that if my webcam is plugged in that when it boots my 2.6.29.6-smp doesnt always catch the "HV7131R image sensor". I presume in this case that gspca ...
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  1. #1
    Linux User
    Join Date
    Mar 2008
    Posts
    287

    Card and device associations


    I have noticed that if my webcam is plugged in that when it boots
    my 2.6.29.6-smp doesnt always catch the "HV7131R image sensor".
    I presume in this case that gspca handles the image sensing.

    If I boot with webcam unplugged I get this order of cards:
    # cat /proc/asound/cards
    0 [V8235 ]: VIA8233 - VIA 8235
    VIA 8235 with ALC650F at 0xe000, irq 5
    1 [Bt878 ]: Bt87x - Brooktree Bt878
    Brooktree Bt878 at 0xdddff000, irq 10
    and my devices are:
    # ls /dev/aud* /dev/vid*
    /dev/audio /dev/audio1 /dev/video0
    If I then plug in the webcam I get:
    # cat /proc/asound/cards
    0 [V8235 ]: VIA8233 - VIA 8235
    VIA 8235 with ALC650F at 0xe000, irq 5
    1 [Bt878 ]: Bt87x - Brooktree Bt878
    Brooktree Bt878 at 0xdddff000, irq 10
    2 [camera ]: USB-Audio - USB camera
    USB camera at usb-0000:00:10.3-1.3, full speed
    # ls /dev/aud* /dev/vid*
    /dev/audio /dev/audio1 /dev/audio2 /dev/video0 /dev/video1

    But if I cold boot with the webcam plugged in I get:
    # cat /proc/asound/cards
    0 [camera ]: USB-Audio - USB camera
    USB camera at usb-0000:00:10.3-1.3, full speed
    1 [Bt878 ]: Bt87x - Brooktree Bt878
    Brooktree Bt878 at 0xdddff000, irq 10
    2 [V8235 ]: VIA8233 - VIA 8235
    VIA 8235 with ALC650F at 0xe000, irq 5

    I am using mplayer and building a set of commands I can invoke to
    play and record. I was getting quite confused when my script would
    work one day and not the next. Apparently it is due to the "fickle"
    way in which the cards are recorded into the system. The card flipping
    I may be able to handle. When I go into /proc/asound/card2/pcm0p
    [the V8235] and "cat info" it indicates to me that playback is
    associated with device 0. pcm0c "capture" is also card 2 and device 0.
    There is also pcm1p and pcm1c which are card 2 and associated with
    device 1.
    I get errors that the device is busy for either or both devices.

    a) How can I know which device 0 or 1 is used by the card as sometimes
    either one or the other is busy?

    b) There are other times when both are busy. Is that when the cards
    get flipped?

    c) What command(s) do I use to determine which device video0 or video1 is the input
    once I know which card the webcam is on?
    I have to double check but I think I have encountered the cards when Bt878 card was in
    the 0 position.
    Can someone clarify this situation for me?
    Last edited by clickit; 08-05-2010 at 10:23 PM.

  2. #2
    Linux User
    Join Date
    Mar 2008
    Posts
    287

    Card and device associations

    I have learned one way to find out which video card is active:
    cat /dev/video0 or 1 whatever
    If the response is "no such" it means device doesn't exist
    if it responds "no space" then device exists but is not active
    if the screen is filled with strange domino characters and unintelligence that is the active device.
    Wave your hand in front of the webcam and the display responds.
    Now, what does it mean if 2 of the video devices respond that way and I have only 1 webcam?
    How do I tell what application has control of each?

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