Re: USB Question: unable to open /dev/ugen0 more than once

From: Bernd Walter (ticso_at_cicely12.cicely.de)
Date: 11/24/03

  • Next message: Dan Langille: "using devel/libusb to access USB" 
    Date: Mon, 24 Nov 2003 14:54:39 +0100
To: "Michael E. Mercer" <mmercer@nc.rr.com>

    On Sun, Nov 23, 2003 at 08:50:45PM -0500, Michael E. Mercer wrote:
    > Hello peoples,
    >
    > I posted this to questions with no reply, I was hoping
    > someone here may be able to give some insight.
    >
    >
    > Question: Should I be able to open /dev/ugen0 more than once?
    >
    > I am using FreeBSD 4.9-Stable, libusb-0.1.7.
    > >From reading the libusb docs, you must open the device for each
    > interface you want to acquire. However, once it is opened once, it can't
    > be opened again.
    >
    > Furthermore, calls to usb_find_devices() shows that /dev/ugen0 has
    > disappeared. Investigation on how they(libusb) finds devices, shows they
    > are trying to open the device read only... this is where it tries to
    > open it the second time. This second try fails and therefore libusb
    > thinks the device was removed.
    >
    > Question: Is this the correct behavior?

    Yes - this is correct.
    A client using ugen on a multiple interface only need to open
    /dev/ugen? for probing only - the work should be done using the
    interface specific endpoints /dev/ugen?.?
    Opening /dev/ugen? read-only makes no sense, because there is no read
    only access possible - /dev/ugen? is for the control endpoint which
    always means sending commands to the device. 

    -- 
B.Walter                   BWCT                http://www.bwct.de
ticso@bwct.de                                  info@bwct.de
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  • Next message: Dan Langille: "using devel/libusb to access USB"

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