On Thursday 03 March 2005 6:55 am, Pavel Machek wrote: > Hi! > > > In most of the cases I'm thinking of, it wouldn't be a user > > requesting a state but rather software (say, a cell phone > > progressively entering lower power states due to inactivity). I > > haven't noticed a platform with more than 3 low-power modes so far, > > Are not your power states more like cpu power states? For System-on-Chip devices it can be a fine line. Maybe six of the most important devices (including CPU) are in a low power state, but some others are still active. > These are expected to be system states, and sleeping system > does not take calls, etc... Pavel, remember that great big "wakeup" shaped hole in the current PM framework... ? Even ACPI sleep states support wakeup mechanisms, although not well under Linux (yet). One way a sleeping system could take a call is if some external chip raised a wakeup-enabled IRQ to wake up the system. And if going from deep sleep to normal operational state has a low cost, why shouldn't the system routinely enter deep sleep instead of going to CPU idle state? It's certainly the case that connecting the USB device to a host can un-gate that peripheral's 48 MHz clock and wake the system up from deep sleep. - Dave
