USB Powered Speakers

[Warren Block]

On Fri, 9 Apr 2010, Programmer In Training wrote:

> On 04/09/10 10:15, Brodey Dover wrote:
>> "Apr  8 22:30:16 heaven kernel: usb_alloc_device:1624: getting device
>> descriptor at addr 3 failed, USB_ERR_IOERROR!"
>>
>> exactly! That is what is causing the issues. From what I can see, it
>> is like it was explained before. The OS has chosen to play nice and
>> request that the speakers are disabled.
>>
>> The power requirements will not affect the system until the speakers
>> are producing sound. In other words, the system will only draw UP to
>> the power input rating while in operation. At idle, I'd wager they may
>> only use 1/10 of its power rating for the idle ICs and a power LED.

Just to add:

When you plug in a USB device, it is a "low power" device (single unit 
load, 100 mA) by default.

If that device wants to draw more power, it has to request high power (5 
unit loads) from the hub.  The hub can provide that power, or shut down 
the port.

> Only it's not the speakers that have their operation interrupted, JUST
> the keyboard (not even the mouse is affected).

Guesses:

Total power budget (but FIFO?).
Speaker/keyboard USB ports are on the same internal hub.
High-power OLED keyboard (my eyes!).
Speakers labelled 500 mA but really only a low-power USB device.

-Warren Block * Rapid City, South Dakota USA