Saturday, April 12, 2008

A Hint in the Quest for S3 Suspend on Windows

Unlike most geeks I know, when I'm working, I don't like to put on headphones and listen to music. I concentrate and focus better in quiet places. So when I put together a new PC, one of my top priorities was quiet. Quiet case, quiet cooling, low power consumption (relative to horsepower) and S3 suspend.

Since I switch between a few different boxes, multiple power supply fans churning in a small room is a loud problem. Plus, S3 is a great user experience (instant restart, exactly where you were) and enviro/energy-bill friendly (far less power consumption than an S1 fake suspend).

Google around and you'll find lots of tips for S3:

  • First, you need to be running the ACPI HAL underneath Windows. Typically not a problem, but you can check under Device Manager / Computer node.
  • Second, check that your BIOS ACPI setting allows S3 (e.g., mine has as option "S1 Only" that would prevent it from going S3 if it were selected)
  • Windows XP normally omits a registry entry (USBBIOSx) required for S3 because apparently some hardware can't wake from it via USB devices. Why that warrants disabling a sleep mode that I've always woken up with the big ol' power button I don't know.

Check the BIOS before you install Windows and the ACPI HAL immediately afterward, because conventional wisdom is you may need to reinstall the OS if you want to change these items.

I did all this stuff, still no S3. What next? There's a Microsoft command-line utility called DUMPPO.EXE which outputs a bunch of useful power management status stuff and lets you set power policy as well.

When I ran it with the cap argument, it produced a report that said no suspend modes were available on my hardware at all! Huh? Whah?

At the bottom of the report is a separate line about a legacy driver. It was the default VGA driver that XP uses on install, since I hadn't loaded the real nVidia driver yet.


I installed nVidia's latest and rebooted -- all of the power options were now enabled. DUMPPO also reported all of the suspend modes available.

So... first, bad, bad Microsoft for defaulting virtually all video hardware to a legacy driver that breaks the OS's own power management. Maybe there's a fix for that in XP SP3.

But second, check ALL of your drivers -- chipset, sound hardware, and video at least, and don't bother testing S3 until after you've gotten your drivers installed.

1 comment:

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