Ejecting/Powering off/ -> Turn off the device lamp.

Ejecting/Powering off/ -> Turn off the device lamp.

[Andy Kennedy]

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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?

Thanks in advance for any help you can give.

Andy Kennedy

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Re: Ejecting/Powering off/ -> Turn off the device lamp.

[Alan Stern]

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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


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Re: Ejecting/Powering off/ -> Turn off the device lamp.

[Andy Kennedy]

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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

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Re: Ejecting/Powering off/ -> Turn off the device lamp.

[David Brownell]

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On Monday 22 May 2006 9:50 am, Andy Kennedy wrote:

> I am working with an embedded system that will have no user interaction 
> save the USB port. ...
> 
> I have TTLs on the embedded system; I may just have to use those.

Sounds like you need to design in some additional user interaction,
either a LED driven by a GPIO to indicate "OK to remove", or else
a LED driven by that port's root hub.  (Some root hubs support the
standardized root hub LED mechanisms; most don't.)

- Dave


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Re: Ejecting/Powering off/ -> Turn off the device lamp.

[David Brownell]

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On Monday 22 May 2006 9:21 am, Andy Kennedy wrote:

> Is there a way to signal the device to stop the cycle and actually power 
> off the LED?

You might be able to ask the device to suspend -- using the deprecated
/sys/devices/.../power/state files -- which in common cases means that
bus-powered devices won't be able to keep a LED powered.

But LEDs are highly device-specific, so there can be no general rules.

- Dave

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