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

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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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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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

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