[time-nuts] Serial port / Mouse issue (was mentioned in"Thunderbolt Monitor")

[Hal Murray]

stephen at tompsett.net said:
> FTDI devices with their device driver should remember the COM port they
> have been assigned on an individual system even if they get plugged into  a
> different port/hub, and this greatly reduces reconfiguration effort if  you
> change any USB connections - Other manufacturer's devices have a  tendency
> to use a new COM port number each time they are plugged into a  different
> physical USB port connected to the same computer. 

The USB protocol has provisions for each device to provide a SerialNumber.  
That lets the OS connect them up at the appropriate logical name no matter 
which physical port they are plugged into.  They have been common on disks 
and thumb drives for a long time.  My printer has one.  So does my scope.

Most low cost USB serial adapters don't (or didn't) have a useful serial 
number.  (Or maybe the Linux drivers don't use it, but I suspect that's done 
at a higher level so it should work for serial if it works at all.)

I have some FTDI adapters that produce useful serial numbers.
   usb 3-1: SerialNumber: A4003UAg
   usb 5-2: SerialNumber: A4001h2X
I'm pretty sure I have other FTDI ones without a serial number.

I don't think I've seen a useful serial number on any Prolific gizmos.  My 
collection includes lots of older gear so my sample may be biased and/or 
things could have changed.

It might be helpful to collect a list of which gear from which sellers 
do/don't have useful serial numbers.

With Linux, the udev stuff will let you setup a /dev/xxx alias when it sees a 
particular serial number.  I'll say more if anybody wants.



-- 
These are my opinions.  I hate spam.