I'd like to maintain power supply to a USB-powered drive when the system goes into suspend (AKA S3 or "suspend-to-RAM") mode.
Normally the power is cut while the machine is suspended, which causes it to be dismounted and then remounted when the system is resumed. This is not really great, especially if the drive itself supports power management.
Although I could run it on a separate power supply, I'd prefer to have to avoid allocating more wiring for something that can, at least in theory, be done with my existing hardware.
How can I determine if it is possible to do this with my system, and how can I arrange for a particular USB device, i.e. this enclosure, to always be treated this way?
I'm running ubuntu 10.10.
Discovered this ubuntuforums thread which suggests to use
acpitool -w to determine the available wake-up level for the USB controller.
Running this on my system shows S1 for the USB controllers:
$ acpitool -w Device S-state Status Sysfs node --------------------------------------- 1. LID S3 *enabled 2. PBTN S4 *enabled 3. PCI0 S3 *disabled no-bus:pci0000:00 4. USB0 S1 *disabled pci:0000:00:1d.0 5. USB1 S1 *disabled pci:0000:00:1d.1 6. USB2 S1 *disabled pci:0000:00:1d.2 7. USB3 S1 *disabled pci:0000:00:1d.7 8. MODM S3 *disabled 9. PCIE S4 *disabled pci:0000:00:1e.0
Which seems to be telling me that wake-up capability can only be enabled for USB in the S1 state.
I'm not sure how useful this is, since providing full power and allowing wake-up may be orthogonal concerns. It may be enabling wake-up only provides low power, so there may be a different way to enable full power.
If turning on wake-up does equate to providing full power, it looks like I may be able to do what I want by putting a USB card in the expansion slot (I guess that's what
PCIE is?). Though I think I'd want to know a bit more about this before attempting to excavate a USB2 PC card.