temp sha wrote: > >> Look closely in the kernel output and you'll see that no ids change, > >> but that the old device has disconnected and a new device has > >> connected. > > sorry I could not get it completely. > what is this new device/ old device ?
A USB device as seen by the kernel is a software concept according to the USB specification and is really unrelated to physical objects. Many physical objects which connect via USB only ever appear in one way, the same way every time, but many also change how they appear, depending on a number of different factors, including being told by software such as a Windows driver or usb_modeswitch to change their appearance and behavior. USB is not a serial port with power. It is a highly structured bus, much more similar to a network. > there is only one device USB dongle. > changing usb mode can change the product id as well ? does it mean product > id is related with usb's mode of operation rather than actual physical h/w. Sure. The physical object is irrelevant to software. What matters is how the object appears and behaves via USB. This is the definition of a USB product. Most of the time it is actually adhered to by vendors. > if yes then what about default and target vendor ids seen in the > usb_modeswitch help cmd? > does this also depend on mode of operation sometimes ? I tried to explain that in the previous email: > >> looking into the help I found 0x1446 is default product id wheres > >> 0x1506 is the target product id. but could not get the idea behind > >> this concept. > > > > The USB modem normally appears as a storage device with the Windows > > software, so that Windows users can easily install it. By this I mean that the storage device is a virtual CD with a Windows driver stored on it. > > The driver needs to tell the modem to switch from appearing as a > > storage device to appearing as an actual modem. usb_modeswitch does > > that. A USB device can not change descriptors (with vid+pid) and behavior on the fly, so the device then disconnects from the host, changes its behavior and reconnects with different descriptors and different behavior. Only then can the kernel modem driver use the modem. //Peter -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
