Re: [libusb] Device changing serial numbers

[Tim R. <ti...@pr...>]

Matthew Giassa wrote:
> Second, addressing your question: yes, transfers using the old device handle succeed. This includes flashing and verifying the bootrom. 

This is impossible to believe.  The device number is the physical
addressing mechanism on the bus.  If the device is now known as device
11, then requests to device 10 will be ignored.

You did say you are working with two cameras.  Isn't it possible you are
getting confused between the two cameras here?  Do both cameras use the
same serial number?  (Windows, for what it's worth, will not allow that
situation  VID/PID/Serial must be unique system-wide.)


> Is it possible that if the device serial number changes without resetting the device we get a "partial" enumeration, or does libusb handle triggering the requisite events if a device randomly changes its serial number and doesn't inform the system?

There's nothing fundamental about the serial number.  It's just another
attribute of the device.  Neither libusb nor the driver stack will
monitor it.

In fact, there's no way for a device to notify anyone that its serial
number has changed.  A USB device never initiates transactions of any
kind.  USB is entirely host-driven.  If you go fetch the serial number
twice in a row and get different answers, well then, you have a clue
that the serial number has changed, but you're the only one with a clue.

In order to get anyone to notice, the device has to drop off of the bus
and reattach, which is exactly like an unplug/replug.  The old driver
stack is torn down, and a new driver stack is created.  Requests through
the old driver stack will fail.

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.