> Suspend is quite different from power-cut as devices are still allowed to
> draw up to 0.5mA from the suspended USB (see 9.2.3, USB spec.). While
> being enough for a pm-aware microcontroler to keep its state information
> (like fn-address, device-config, interface alternate setting) in the
> microcontroler registers, it's probably insufficient to keep the firmware
> running or even to have an external ram powered. Hence the device _does_
> keep its state, but needs to reload firmware (or parts of) on resume.
>
> And the device might simply use an eeprom to save and restore its state
> during suspend/resume. The required state information can be reduced to
> only a few bytes - which are easy to write to some eeprom during the
> 10ms the device may take to complete suspending.
We cannot assume that the host controller will be powered at all.
In fact at some time we will face suspend to disk which will cut power
altogether. Furthermore the pure usb device state might nopt be enough.
A camera for example may have gamma correction, compression ratio, etc ...
While a device might implement a number of nice features, we are bound to
meet a lot which don't.
Regards
Oliver
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