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ACPI Forced On & Option Disabled in WinXP-Certified Motherboards
stealth_zipper asks: "I just got off the phone with a rep from Soyo Computer Inc trying to get the ability to change IRQs for the onboard hardware. It turns out that because of a deal to get WindowsXP certification, the Dragon-series motherboard ended up having the ability of Enabling/Disabling ACPI in the BIOS disabled. Now FreeBSD has complications with multiple devices on the same IRQs (especially sound, video, and nic all off the same one). Is there a way to get around this for new hardware? Has anyone else encountered this?" Why in the world does XP need this feature disabled, and are there workarounds to get OSes like FreeBSD working properly with motherboards of this sort?
wouldn't this easily add to their antitrust case?
microsoft makes so many smart moves.
Runnin' On Empty
Are you sure that's the problem? These boards are having *tons* of problems, the P4 ones in particular.
I work at a computer shop in Wisconsin and we've gone so far as to stop carrying them because of the problems.
DOA.... bad slots.... bad ps/2 ports... "nothing after POST"... you name it.
I'd just make sure that it's ACPI causing the problem and not a defective board.
-kwishot
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Because ACPI is deprecated, in favour of APM. Is that a good enough reason? God forbid we should actually move forward and embrace new standards.
Good try, but in fact the reverse is true: APM is deprecated, and ACPI is the new standard.Some of the things that Microsoft has forced us to change in the past few years include:
- One of our main products was in full compliance with the IEEE
specification for the USB interface. However, because Windows 2000 used a
while() loop for a timing operation, it was sometimes flaky when dealing
with our product. As a result, we needed to re-engineer an ASIC (this was
damn expensive) to make it compatible. The original version, of
couse, was fully compatible with Linux.
- Normally Windows communicates in a little-endian fashion. However, for
two particular device status operations, Windows inexplicably violates yet
another published spec and forces the device into big-endian (mac fag)
mode. We needed to change firmware to fix this, and delay the release of
our product by 3 weeks.
- Microsoft required that the source code to our Windows drivers got
audited in order for the product to be approved. Hmm, why don't they let
us audit their code?
Naturally, though, since the DoJ has dropped the ball on Microsoft, this sort of thing will only get worse. Get used to it, and vote Democratic in 2004.Bill
If you read the article it says "It turns out that because of a deal to get WindowsXP certification, the Dragon-series motherboard ended up having the ability of Enabling/Disabling ACPI in the BIOS disabled."
This means that ACPI is always ON, not off.
In the shortest way I can explain it, changing ACPI from on to off or vice versa on a current install of Windows 2000 or XP will... "fuck shit up." A more detailed description of how/why "shit gets fucked up" follows:
In Windows, peripheral component interconnect (PCI) devices can share IRQs. In accord with the Plug and Play capability that is defined by the PCI specification, adapters are configured by the computer BIOS and are then examined by the operating system and changed if necessary. It is normal behavior for PCI devices to have IRQs shared among them, especially on Advanced Configuration and Power Interface (ACPI) computers that have Windows ACPI support enabled.
In Windows XP, Device Manager may list some or all of the devices on your ACPI motherboard as using the same IRQ (IRQ 9). (To view the list of resources, click either Resources by type or Resources by connection on the View menu). No option is available to change the IRQ setting. Windows takes advantage of the ACPI features of the motherboard, including advanced PCI sharing. The PCI bus uses IRQ 9 for IRQ steering. This feature lets you add more devices without generating IRQ conflicts.
Note that Windows XP cannot rebalance resources in the same way that Microsoft Windows 98 does. After PCI resources are set, they generally cannot be changed. If you change to an invalid IRQ setting or I/O range for the bus that a device is on, Windows XP cannot compensate by rebalancing the resource that was assigned to that bus.
Windows XP does not have this ability because of the more complex hardware schemas that Windows XP is designed to support. Windows 98 does not have to support IOAPICs, multiple root PCI buses, multiple-processor systems, and so on. When you are dealing with these hardware schemas, rebalancing becomes risky and therefore is not implemented in Windows XP except for very specific scenarios. However, PCI devices are required to be able to share IRQs. In general, the ability to share IRQs does not prevent any hardware from working.
The Plug and Play operating system settings in the computer BIOS do not generally affect how Windows XP handles the hardware. However, Microsoft recommends that you set the Plug and Play operating system setting to No or Disabled in the computer BIOS. For information about viewing or modifying the computer BIOS settings, consult the computer documentation or contact the computer manufacturer.
Manually assigning IRQs to PCI slots in the system BIOS as a troubleshooting method may work on some non-ACPI systems that use a standard PC hardware abstraction layer (HAL), but these settings are ignored by Plug and Play in Windows if ACPI support is enabled. If you need to manually assign IRQ addresses through the BIOS to a device on an ACPI motherboard, you must reinstall Windows to force the installation to use a Standard PC HAL. For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
More info can be found he'a...
First of all, ACPI was created to a) make computers that "boot" instantly by always being in sleep mode and b) end the IRQ conflicts so common with earlier versions of Windows and hardware. So yes, ACPI, when working right, simply rocks.
However, ACPI on certain motherboards, especially AMD motherboards, can cause severe system instability with Windows 2000 and Windows XP. (Please note that these OSes don't freeze/BSOD under normal circumstances, so if you're seeing this, you probably have a hardware issue which could be related to ACPI.)
The most common scenario I have seen is this:
-- Someone decently technically savvy builds his/her own PC with an AMD chip;
-- Said person installs Windows XP;
-- Said person wonders why IRQs are all set to 9;
-- Said person goes and manually messes with IRQ settings, thus wreaking havoc on the poor commputer that functioned perfectly before.
It can also go the other way:
-- Said person installs Windows XP with AMD chip;
-- Said person experiences weird freezes;
-- Said person's computer works fine with Windows 98 because Win98 doesn't have full ACPI support, so person is left wondering why everyone says that Windows 2000 and Windows XP are so stable since that person's computer crashes constantly.
To turn off ACPI, reinstall Windows and set your computer type to "Standard PC." Here is an excellent guide on how to set your PC to a Standard PC. As mentioned in the guide, this gives you the added benefit of increased framerates in Quake 3. However, you have to manually turn your computer off, and it might not go into powersave mode properly. Here is another comment regarding ACPI.
So, to summarize:
-- If you're having problems with Windows 2000/XP freezing, try this fix. Freezes are indicative of a hardware issue. Your computer should be stable with these OSes (except for application crashes, which happen with every OS.) My current uptime with Windows 2000 is 27 days; I have seen over 100 days uptime. If you're not seeing this type of stability with 2000/XP, it's time to do some hardware diagnostics.
-- If you're not having problems, leave well enough alone and leave ACPI turned on.
-- Do NOT mess with your IRQs on an ACPI computer! By messing with IRQs manually, you're asking for weird system problems. Leave them all on 9 -- it won't hurt the computer.
-- Due to the problems mentioned above, I personally will not buy AMD chips and motherboards. I have yet to see ACPI problems crop up on an Intel motherboard. It's unfortunate, because I like AMD and like to encourage competition, but their chips and motherboards have strange issues that have yet to be resolved.
I hope this helps all of you who are having problems with Windows XP or 2000.
Simpli - Your source for San Jose dedicated servers and colocation!
That headline really needs to be changed. It should read something like "ACPI Forced On in WinXP Certified Mobos"
Also, did anyone else notice this little gem on the requirements page?
Does this mean hardware support for DRM in sound cards?
If a device only generates an interrupt every second or two, but the CPU takes 500mSec to service that interrupt, that means that everything else using that IRQ is left out in the cold for that time. (This is the Interrupt Latency)... even a 1Ghz P4 won't be able to play sound without breaking up if this happens... which is just plain stupid.
Video, Network, and Disk devices obviously have different requirements and should each have their own interrupt. This insane sharing of IRQs should end.
--Mike--
This was posted by an MS guy to the OSR NTDEV listserv:
The early ACPI machines were mostly laptops. And the laptops of that generation had most of their devices either embedded in the chipset or on the ISA bus. The PCI or AGP buses were used only for video, and to connect the north bridge with the south bridge. (In Intel's chipset terms, the North bridge has all the fast gates of the chipset, including the memory controller, AGP and in that generation, the PCI bus generation logic. The south bridge contains all the slow gates, including the IDE controller, the ISA bridge, all the PC legacy stuff and probably a USB controller. Today, the south bridge probably also has audio and a few other random odds and ends.) Because the laptops of that era had all of their devices on the ISA bus, interrupt sharing worked poorly. If you bought a mid-'90s laptop from IBM or Toshiba, the serial port and possibly IR would be disabled. There would be a utility packaged with the machine that allowed you to turn on your serial or IR, but at the cost of the bi-directional parallel port, or one of the PCMCIA slots, since there just weren't enough IRQs in the machine to guarantee that all of the peripherals worked, especially if you filled both PCMCIA slots with combo cards.
I once debugged a Toshiba 750CDT in a docking station that had two PCMCIA cards plugged into the machine, two PCMCIA cards plugged into the slots in dock, two ISA cards in the dock and an extra IDE device in the dock, too. This meant that the total demand on the machine was 20 IRQs, when only 16 were actually available.
(As an aside, I've been trying to convince Intel to put APIC interrupt controllers, which would allow many more IRQs, in their laptop chipsets since 1997. My predecessor had been trying since '94. They may actually manage it soon.)
Along comes ACPI. When you turn on ACPI in a machine, it suddenly switches all the power management logic in the machine from delivering its interrupts as BIOS-visible, non-vectored System Management Interrupts over to OS-visible, vectored interrupts. And that interrupt is delivered level-triggered, active-low, which means that it can be shared with a PCI interrupt.
Now consider that these early ACPI machines were already over-committed in terms of interrupts. There was no way to make them work with PCI devices spread out on lots of IRQs. So I just made the code collapse all the sharable devices onto the ACPI interrupt, which was fixed in the chipset by Intel at IRQ 9. By doing it this way, I could hide the fact that ACPI had just created a demand for one more IRQ. (If you use a non-Intel chipset that has ACPI coming in on some other IRQ, you'll see all the PCI devices in Win2K go to that IRQ, not 9.)
Further complicating this story was that I was trying to get ACPI machines to work back in 1997, when the people working on Plug and Play in Win2K hadn't yet gotten their stuff going yet. At time, it wasn't possible to move a device from one set of resources to another after it had been started. This meant that any IRQ solution that I came up with had to work from the first try, so it had to be conservative.
The everything-on-IRQ-9 solution worked. It got the machines to run, as long as none of the device drivers mis-handled their ISRs. (Later, this turned out to be a huge debugging problem, since when you chain eight or nine devices, you'll get somebody who fails.) The solution wasn't optimal, but it did work. I meant to go back and change it later, before we shipped Windows 2000.
A couple of years passed. I had been working on multi-processor problems and on other aspects of ACPI. It got close to the time to ship Windows 2000 and somebody brought up the old question of IRQ stacking. I worked up a more-elegant solution, one that spread out interrupts on most machines. By that time, Plug and Play had been mostly completed, and that wasn't a bottleneck any more. But the test team told me that they wouldn't let me put it into the product, since they didn't have time to re-test the thousands of machines that had already been tested with the old algorithm.
At the time, I thought that this was somewhat ridiculous. I thought that my code would work just fine. I thought that their fears were un-justified. But I was overruled, and I just put the code into what became Windows XP, letting Windows 2000 ship with the simple, safe, yet frustrating stacking.
This is a good point in the story to explain that, in ACPI machines, the IRQ steering is accomplished by interpreting BIOS-supplied P-code called ASL. The IRQ routers are completely abstracted by the BIOS. The OS doesn't need to know about the actual hardware. The old IRQ steering code in Win9x, which was dropped into the non-ACPI HAL in Win2K, had to have code specific to each chipset, which meant that it didn't work when new chipsets were shipped. It was also written in a way that it assumed that there were exactly four IRQs coming from PCI. ACPI machines sometimes have many more. (This is the reason that you don't see the IRQ steering tab in ACPI machines. It just wasn't flexible enough and we didn't have time to re-do it.)
What we discovered with Windows XP was that all of those ACPI machines that had been tested with their IRQs stacked on IRQ 9 tended to fail when you spread the IRQs out. A typical example of a failure would work like this: WinXP doesn't need the IRQ for the parallel port unless you're using one of the extended modes. So the parallel driver releases its IRQ until it's needed. The IRQ choosing logic (called an IRQ "arbiter") would move a PCI device onto the parallel IRQ. This action depends on re-programming the chipset so that the parallel port isn't actually triggering the IRQ. This is supposed to happen by interpreting even more BIOS P-code that manipulates the chipset, since there is no standard for parallel port configuration.
If your chipset comes from Intel, this probably works, since the mere act of setting a PCI device to an IRQ also disconnects that IRQ from the ISA bus. But if your chipset comes from VIA or ALi, there is another step involved. The problem is that nearly all of the BIOS P-code out there is copied from old Intel example code. So they are almost all missing the extra step necessary in VIA and ALi machines.
If the BIOS fails to stop the IRQ coming from the parallel port, the machine hangs, since the parallel port, which sends its IRQs active-high, edge-triggered, will ground the interrupt signal in the passive state. And grounding an interrupt which is enabled active-low, level-triggered will cause an endless stream of interrupts. The parallel port is just an example. Pick any device that is in the legacy SuperIO chip and the story repeats itself.
In Windows XP, I made a bunch of changes. In machines without cardbus controllers, (which don't have the IRQ problems created by PCMCIA,) it will try to keep the PCI devices on the IRQs that the BIOS used during boot. If the BIOS didn't set the device up, then any IRQ may be chosen. But if your machine has a VIA chipset, or if it has a BIOS that we know to be broken, then we fall back to the Win2K-style stacking behavior. The unfortunate truth is that you guys on this list mostly build your own machines, rather than buying them from reputable manufacturers, which means that you guys own the machines with broken BIOSes and VIA chipsets. So even with WindowsXP, you'll see the same old stacking behavior.
One notable addendum is that any machine with an APIC interrupt controller, and thus more than 16 IRQs, will spread interrupts out, even in Win2K. In the past, this was mostly limited to SMP machines. But any desktop machine shipping today that gets the Windows logo has to have an APIC. (This was another reason that I hadn't gone back to re-write this code earlier. Intel had promised that all machines would have APICs by 1998. If this had materialized, then none of you would have had any complaints by now.) I'm actually currently working on software for some future NT that will let an administrator configure the
machine in any way he or she desires.
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
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