some notes about usb

A few random notes about USB-support of serial devices 
(unslung 3.xx): 
 
(1) Many usb-serial adapters use the prolific chipset which is 
handled by the kernel module pl2303.o. Newer versions of this 
chipset require a patch to this driver which is not included in 
the current openembedded environment: 
<http://koti.mbnet.fi/lonnberg/pl2303x.html> 
Unfortunately, there is no error message if this patch is 
not applied. The chip is detected and attached correctly as 
shown by 'dmesg' but it won't work. 
 
(2) The NSLU2 kernel is not compiled with hotplug enabled (or am  
I missing something?). This is problematic if several serial devices 
are attached (in my case a printer and a Palm Tungsten). There is no 
simple way to detect which ttyUSBx port is connected to which device 
(other than parsing `dmesg`). I added a simple hotplug hook to 
usbserial.c which now calls a hotplug script whenever a serial 
device is attached or removed. If someone is interested I could post 
this patch. 
 
(3) Coldplugging any usb device does not work if the NSLU2 is run 
with a mass storage device attached to "Disk 2" (in my case a 
CF-card reader): If any usb device (serial adapter, Palm PDA, 
digital camera, or even a simple hub) is attached to the "Disk 1" 
port during bootup, the mass storage device at "Disk 2" is not 
detected. There is no problem attaching it later, but it is somewhat 
tedious to remove all devices during bootup. 
 
 





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