On Feb 12, 2006, at 22:52, Phillip Susi wrote:
Alan Stern wrote:
It's not just semantics. There's a real difference between
maintaining state in the hardware and maintaining it somewhere
else. The biggest difference is that if the hardware retains
suspend power, it is able to detect disconnections. When the
system resumes, it _knows_ whether a device was attached the
entire time, as opposed to being unplugged and replugged (or
possibly a different device plugged in!) while the system was
asleep. If the hardware is down completely, there is no way of
telling for certain whether a device attached to some port is the
same one that was there when the system got suspended.
During suspend the hardware is usually completely powered off,
This is true for software suspend, but not for hardware suspend (see
the differences now?) This is why the two are independent and should
not be mashed together into one "Generic Suspend". Let me bring up
the example of my PowerBook again. It's RAM is fully powered right
now, running from battery, and it has another couple days of sleep-
charge left before I have to worry about plugging it in again. When
I open it, the firmware automatically powers up the CPU and other
hardware and returns control to the OS. I can _also_ trigger it to
wake by leaving it closed and connecting an external VGA and USB (it
wakes every time I connect a USB, but my suspend script puts it to
sleep again if it's closed and has no external VGA).
and in either case, there is nothing running on the CPU to monitor
device insertion/removal.
You don't need the CPU, just a good USB controller and hubs with low-
power modes and such. The fact that plugging in a USB keyboard/mouse
and a VGA monitor is enough to wake the system when properly
configured should be proof enough.
When the system is resumed the kernel decides if the hardware has
changed the same way for either system: it probes the hardware to
see if it is still there. There isn't anything special that
monitors device insertion/removal while suspended to ram.
Sometimes not, but again, it depends on the hardware.
Cheers,
Kyle Moffett
--
I have yet to see any problem, however complicated, which, when you
looked at it in the right way, did not become still more complicated.
-- Poul Anderson
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