Re: [pyusb-users] Initializing several interfaces of the same device

[wander.lairson <wan...@gm...>]

2011/3/15 Emmanuel Blot <ebl...@gm...>:
> Hi,
>
> I bumped into an issue when initializing a device.
> The device (FTDI chip) offers up to four similar UART/serial ports,
> each port is tied to a USB interface.
>
> I use the following piece of code:
>
>    dev = usb.core.find(idVendor=vendor, idProduct=product)
>    if not dev:
>        raise IOError('Device not found')
>    for configuration in dev:
>        for interface in configuration:
>            ifnum = interface.bInterfaceNumber
>            if not dev.is_kernel_driver_active(ifnum):
>                continue
>            try:
>                print "detach %s: %s" % (dev, ifnum)
>                dev.detach_kernel_driver(ifnum)
>            except usb.core.USBError, e:
>                pass
>    dev.set_configuration()
>
> I need to detach *all* the interfaces from the (Linux) kernel, or I
> sometime get an error (not a big deal for my use case)
> I also need to call dev.set_configuration() to configure the device.
> Nothing unusual I guess.
>
> The troubles happen when I need to open two serial ports, that is two
> interfaces from the same USB device.
> On the second initialization call, when dev.set_configuration() is
> called for the second time, the first open interface gets in trouble:
>  Exception: UsbError: No such device (it may have been disconnected)
> It seems set_configuration() cannot be called another time if an
> interface is already being actively used.
>
> I don't know how to avoid calling set_configuration() more that once,
> as I don't know how to identify that the USB device has already been
> configured.
>
> Each call to usb.core.find() returns a different instance even when it
> manages the same device, and I don't see any way to detect the
> physical device has been already configured or not.
>
> Any idea?
>
You can use get_configuration method to check if the device is already
configured. According to USB Spec, if it is not zero, it is
configured.

-- 
Best Regards,
Wander Lairson Costa
LCoN - Laboratório de Computação Natural - Natural Computing Laboratory
(http://www.mackenzie.com.br/lcon.html)
Programa de Pós-Graduação em Engenharia Elétrica (PPGEE)
Faculdade de Computação e Informática (FCI)
Universidade Presbiteriana Mackenzie - SP - Brazil