Alan Stern wrote:
> On Mon, 22 May 2006, Andy Kennedy wrote:
>
>   
>> All,
>>
>> I have done an extensive search on this issue and cannot find the answer 
>> to my specific question.  Whereas I understand that an individual device 
>> on a USB host (on board) cannot be "powered off" nor "ejected" I wonder 
>> if the device can be sent a command from userspace to turn off it's LED 
>> indicator lamp.  Most of the devices that I have seen, when the device 
>> is no longer in use, goes into a blink cycle.
>>
>> Is there a way to signal the device to stop the cycle and actually power 
>> off the LED?
>>     
>
> It's hard to answer that question without knowing what kind of device
> you're talking about.  Some USB devices (like hubs) can be told to turn
> off their indicators; most cannot.
>
> Alan Stern
>   
Very sorry. . . I did leave out the most important part:  I am working 
with various flash disks / USB mass storage devices.

I am working with an embedded system that will have no user interaction 
save the USB port.  The unit will recognize the mass storage device via 
the hotplug scripts, then execute a series of commands. . . after which 
the device will be unmounted and then could be removed.  That is the 
purpose for wanting to extinguish the lamp.  It would be hard to explain 
to a lay person to "Watch the little light.  It should blink very fast 
for a few seconds/minutes then blink slow for a few seconds, then fast 
again. . . then you can remove it." and expect them to comprehend the 
meaning of the "little blinking light."

I have TTLs on the embedded system; I may just have to use those.

Andy Kennedy